Let's Talk Bolt Thrust

Sixgun · Post by **Sixgun** » Thu Oct 17, 2013 3:29 pm

Tin Man has a post asking about loads for his 45 Colt Uberti rifle. He got a few answers from well meaning individuals, but something I have suspected for a long time and was pretty much proven in the latest issue of Handloader by one of my most respected gun writers, John Barsness, and that is, with LOW PRESSURE CARTRIDGES, there is very little bolt thrust.

People talk "bolt thrust"' which is the backward pressure on the face of the bolt during ignition of a cartridge. Sure, we all feel the recoil so it must be true. But not so fast.

At the time of ignition, the fired cartridge exerts pressure all the way around the case, with the case walls taking most of it and over riding the back, but pushing the bullet on to its target. This physics stuff is over my head, but John explains it pretty well.

P.O. Ackley wrote in his book that while doing experiments with his wildcats, he took out the bolt lock of an 1894 Winchester and fired it with just his hand holding on the back of the bolt. This was with the 30-30 AI.

I'll tell you why I have always suspected it. REMEMBER NOW, LOW PRESSURE CARTRIDGES

I have several Colt Lightning rifles of which 2 are of the first model, made in 1884 and 1886. Neither one has an action lock but does have this little lever you can push to keep it closed while walking around. When it comes time to shoot, you just pull the hammer back and let them fly. The lever releases and each cartridge is fired as fast as you can pump the rifle with the pressure of your "pump hand" keeping the action closed. Virtually no thrust on the bolt at all.

I've owned Early model Marlin pump guns in 32-20 and 25-20 that worked the same way. I do remember with those that if the cartridge was loaded above factory levels, the action would open an inch or so, by itself.

The people who make rifles know what they are doing and I personally believe it is entirely safe to shoot replicas of old designs a bit warmer than the 14,000 psi that the factories load the stuff to, like the 45 Colt, 44-40 etc. The liability for the ammo manufactures comes with the old original guns, like the Colt SAA that uses iron for its early cylinders. I'm not saying pushing this stuff like 454's but going to the mid-range pressures of 18,000 is entirely safe and will not "shoot the gun loose".

I could write more but most people get bored after 4 or 5 paragraphs.

I'd like to show the entire article, but I think things like this are against the law.-----Sixgun

Blaine · Post by **Blaine** » Thu Oct 17, 2013 3:58 pm

That's a gun topic.....

JerryB · Post by **JerryB** » Thu Oct 17, 2013 5:46 pm

Thanks Sixgun, I think the self claimed experts have trouble with facts. I reckon that any type of action can be abused but sensible loads should be OK.

AJMD429 · Post by **AJMD429** » Thu Oct 17, 2013 5:53 pm

There is also the matter of 'inertia' that the bolts are often fairly big chunks of steel, vs. a relatively small and soft chunk of mobile lead on the other side of the explosion/burn. If the bullet only weighs 1/20th of the bolt, it stands to reason that if both were just stuck in/on a barrel on opposite sides of a powder charge, the bullet would go flying with equal energy the other way, which would translate into lots of acceleration/speed, whereas the acceleration/speed of the bolt would be a bunch less. Either the square root of 1/20th or the square of 1/20th, but it's the end of the day and my brains 'physics' department has gone home for the day.

EdinCT · Post by **EdinCT** » Thu Oct 17, 2013 7:42 pm

I always wondered about the 357and now the 44 mag in 1873 replicas. We were taught that the weak toggle would shoot loose in a few rounds. I ask how can they work in a revolver with no case head support ?

missionary5155 · Post by **missionary5155** » Thu Oct 17, 2013 8:15 pm

Greetings
I make no claims as an interrior balistics orientated individual.
I do know Ken Waters in his Reloading Manual spent a good amount of time refering to bolt thrust and limitations of certain rifles.
I do know "Nate" of Steves Gun Works highly advises against using "hotter than origonal pressure" loads in even new "steel" 1873 replicas because of bolt thrust.
So as a reloader I have to scratch my head and say.. I defer to the side of caution. Some very knowledgable fellers who have very intimate workings with lever gun systems have stated "bolt thrust" is real and causes receivers to stretch or other parts to go out of specs.
In my own limited experience with a couple origonal 1873 rifles I do know one 32-20 that had suffered enough of some reward bolt forces that the bolt would not close completely and new brass would be reformed with the shoulder moved a good distance forward.
I have read that the Model 1876 was also suffering from the same problem. Something was pushing hard enough on the bolt to either stretch the frame or "crush" the toggle system.
I have a Model 1892 that has suffered enough previous something on the bolt that the frame is either stretched or the bolt is too short for thr receiver.
Maybe I do not understand what is being stated but if bolt thrust is not real.. why do the toggles on the models 73 and 76 have to be locked up in line to bear the bolt pressure ? What causes frames to stretch ? Why are there "custom length toggle sets" available for those 1873 rifles that have excessive head space ?
So if I am misunderstanding something please enlighten me. One thing I know for sure .. I am not ready to remove the locking levers on my 1892 44-40 and pop a round with just the hammer spring and hammer inertia there to hold it all closed.
Mike in Peru

Griff · Post by **Griff** » Thu Oct 17, 2013 8:20 pm

In revolvers the recoild shield absorbs what the bolt does in the way bolt thrust. But, more specifically, my question remains about .45Colt Uberti rifles and their generous chambers. How does that factor in on bolt thrust. But, thinking about it caused my head to hurt... small internal explosion, I'm sure... but generated a random thought... I wonder if the method of measuring headspace using Plasti-gage could be used to measure the amount of bolt thrust from a fired round... hmmm... an experiment in the making! If I end up with next week off... (oh heaven for me.... but my wife'll be livid), maybe I'll do some 'sperimentin'....!

I know that it won't be measureable in the "psi" range, but... if you have a headspace of .003" and that gets reduced to say... .001" under firing... wouldn't that indicate you have x amount of bolt thrust?

PriseDeFer · Post by **PriseDeFer** » Thu Oct 17, 2013 8:24 pm

It's real and with strongly tapered cases it's realer.

AJMD429 · Post by **AJMD429** » Thu Oct 17, 2013 9:17 pm

Griff, I like the experiment idea...!

missionary5155 wrote:Some very knowledgable fellers who have very intimate workings with lever gun systems have stated "bolt thrust" is real and causes receivers to stretch or other parts to go out of specs.

Maybe it's more of a 'peening' effect than a sustained thrust. The guy who used his hand on the bolt would have supported that type pressure - i.e. if you hold an ounce or two of soft, older-gun steel, someone tapping it hard enough to peen it wouldn't move your hand much, yet a sustained pressure of only a few hundred PSI would push past your ability to hold it.

Sixgun · Post by **Sixgun** » Thu Oct 17, 2013 9:47 pm

John Barsness mentions that in high pressure cartridges, the pressure is the same on the chamber walls and the case head but in 1890's lever actions, there is little to none.

What I can attest to is the early Colt Lightnings I have. There is no action lock whatsoever on the early models.

That's why we are seeing reproduction 1873's in 357 mag.

My buddy Gunny has an 1873 Uberti 44-40 with at least 3,000 rounds of warm loads and its tight as the day it was made. He was loading a top load of 5744 with a 240 grain bullet for the 200 meter rams.

Another thing I can attest to and that's when I blew up that 45-90 1886. The bottom of the barrel blew. Look at pictures of blown up revolvers...its always the cylinder...weak link? maybe. I once had a Smith & Wesson Model 53 in 22 Jet. That gun would lock up with the case against the recoil shield if any hint of oil was in the cylinder or the cases---6

KWK · Post by **KWK** » Thu Oct 17, 2013 10:06 pm

Sixgun wrote:... Barsness, and that is, with LOW PRESSURE CARTRIDGES, there is very little bolt thrust.

Barsness is also one of my favorite writers on shooting, but he is a biologist by training, not an engineer. His explanation of bolt thrust is simplistic to the point of being wrong. He appears to not distinguish between stress, pressure, and force and ignores the effect of strain. He is correct that low pressure cartridges can have little to no bolt thrust -- but not for the reason he gives.

BenT · Post by **BenT** » Fri Oct 18, 2013 6:41 am

I enjoyed John's article. It's good that magazines bring up these topics from time to time.

Post by **Chuck 100 yd** » Fri Oct 18, 2013 6:30 pm

We often see .30-30`s that will leave the primer off seated a few thousandths showing excess head space. If there was measurable rear thrust on the case the primers would be seated back in when the round reaches peak pressure.

On the other hand Winchester, Marlin and others don`t like to do excess machining and usually don`t go out of their way to include unneeded parts in a design. If the locking bolt was an unneeded part then why do they include it???

Sixgun · Post by **Sixgun** » Fri Oct 18, 2013 6:40 pm

Chuck 100 yd wrote:. If the locking bolt was an unneeded part then why do they include it???

Easy, it keeps the action closed, is needed if a heavy load finds it way in the chamber, and does give a bit of peace of mind when hammering away with ammo.

Some guns will fire without the action being all the way closed and that can be dangerous. My BIL fired such a gun like that and brass came out and lodged in his eye. The gun was a well known model from Winchester. I experimented with a same model gun and found that a cartridge can go off with the cartridge 1/4" out of the chamber.

Action locks are a good thing.

----6

AJMD429 · Post by **AJMD429** » Fri Oct 18, 2013 10:13 pm

Sixgun wrote:Action locks are a good thing. ----6

Yup. If a gun will fire without the action locked, or a revolver without the cylinder aligned, I am likely NOT to continue shooting it...!

(...granted, that means I won't be shooting some 'classic' antiques, but I have to admit I'm biased towards 'modern' firearms...)

3leggedturtle · Post by **3leggedturtle** » Fri Oct 18, 2013 10:23 pm

AJMD429 wrote:
Sixgun wrote:Action locks are a good thing. ----6
Yup. If a gun will fire without the action locked, or a revolver without the cylinder aligned, I am likely NOT to continue shooting it...!

My cylinder pin retaining thingy on my OM Single Six fell out without me noticing. Saw stuff and pieces flying out of both sides of cylinder when I shot it, Also firing pin put nice marks in cylinder.

El Chivo · Post by **El Chivo** » Sat Oct 19, 2013 2:53 am

once I left case lube on the rounds, I was shooting Trail Boss. The lever popped open almost every round, and I was trying to squeeze it closed.

With hotter rounds, this did not happen. Not sure if it was lube or what.

M. M. Wright · Post by **M. M. Wright** » Sat Oct 19, 2013 6:11 am

I think it's the lube. Ackley cautioned that the chamber was wiped dry and the case was clean and dry with no oil. When fire forming AI brass it needs to be lubricated on the neck and shoulder area.

earlmck · Post by **earlmck** » Sat Oct 19, 2013 10:58 am

After reading the article and everybody's comments I can see that this "bolt thrust" issue is much more interesting, relevant, and maybe complicated than I ever suspected.

From the article I was understanding that "bolt thrust" didn't occur until you exceed some brass strength level, around 57 to 60K psi. I know that isn't exactly true just because my "test" for when I am exceeding factory pressure level of the 30wcf is that my old worn Win94 will pop the lever open at that pressure level (somewhere just above 40K psi). And comments here indicate similar experience -- Sixgun's 22 jet cartridge locking up the cylinder when lubed would be a 40K psi phenomenon.

This has got my head working and maybe hurting thinking of this stuff -- I just always "assumed" that bolt thrust was directly proportional to chamber pressure and even though I had read Ackley's book I had somehow glossed over his AI "no bolt thrust" observation.

So maybe low-pressure rounds have zero bolt thrust, mid pressure rounds have some bolt thrust which may increase if there is lube in the chamber, upper-mid pressure rounds drop back to very little bolt thrust again even with lube in the chamber, and high pressure rounds have full bolt thrust and lube is irrelevant? And maybe we don't know just what those low, mid, upper-mid, and high pressure levels are, and maybe that changes with brass thickness and cartridge shape? Is that a fair approximation of what we may glean from this discussion?

Thanks much for posting the topic, Sixgun. Sure has got me thinking of all the stuff I don't really know that I thought I knew!

Old Ironsights · Post by **Old Ironsights** » Sat Oct 19, 2013 11:39 am

EdinCT wrote:I always wondered about the 357and now the 44 mag in 1873 replicas. We were taught that the weak toggle would shoot loose in a few rounds. I ask how can they work in a revolver with no case head support ?

Note that Winchester is releasing a brand spankin new "1873" in .357 this year...

For now, the 1873 is available only in .38 Spl./.357 Mag. chambering, in deference to the target customer base. The widespread availability of ammo and components in this caliber, along with its lack of recoil makes it the most popular caliber in that circuit. I have been assured by Scott Grange at Browning/Winchester that the original .44-40 WCF chambering is forthcoming, probably along with .45 Colt, which the rifle was not originally chambered for. Due to a lack of popularity, I doubt that other chamberings like .38-40 WCF and .22 LR will be made.

http://www.americanrifleman.org/article ... winchester

Sixgun · Post by **Sixgun** » Sat Oct 19, 2013 1:50 pm

Earlmck,
John writes that lube loses it's properties after 10,000 psi and that it cannot set the case back after that level. Go and read it and see if I interpreted it correctly.

That part does not make sense to me as, well, I told you about the 22 Jet. Even high midrange loads locked up and I'm sure they were running 30-35K.

Where's Einstein when you need him?

Griff, you there?----6

Griff · Post by **Griff** » Sun Oct 20, 2013 1:29 pm

Sixgun wrote:Griff, you there?----6

Wasn't... but am now. Was out in the barn reloading ammo for experimentin' tomorrow.

Here's what I'm thinkin' (dangerous for anyone in close proximity, I know):

Guns, all .45 Colt: 1 -1873 Uberti clone, 1986 production; 2- 2007 production Uberti 1860 Henry Clone; 3 - 2004 model 1892 Rossi short rifle.

I have loaded the ammo, a baseline round of 2 rounds for each gun of new Starline .45Colt cases loaded with 11.5grains of BlueDot under a actual weight of 253grains Speer JHP with WLP primers; and additional two rounds loaded with the same load, but once-fired brass. An additional four loads have been loaded with 12.9 grains of BlueDot under the same bullets in new and once-fired brass, (these will be for testing in the 1873 & Henry only). Plus one nickel Winchester case at the 12.9 grain level along with 2 brass Winchester once-fired cases.

And for comparison's sake, I've loaded 5 of my 45-225-CAV cast bullets over 12.9 grains also.

buckeyeshooter · Post by **buckeyeshooter** » Mon Oct 21, 2013 8:47 am

KWK wrote:
Sixgun wrote:... Barsness, and that is, with LOW PRESSURE CARTRIDGES, there is very little bolt thrust.
Barsness is also one of my favorite writers on shooting, but he is a biologist by training, not an engineer. His explanation of bolt thrust is simplistic to the point of being wrong. He appears to not distinguish between stress, pressure, and force and ignores the effect of strain. He is correct that low pressure cartridges can have little to no bolt thrust -- but not for the reason he gives.

BINGO!!!! John Barsness is NOT an engineer! I'll trust an engineer on stuff I don't understand about bolt thrust!!

Post by **Old Savage** » Mon Oct 21, 2013 9:35 am

John brings up some interesting subjects. Don't know the approach he takes yields the correct answers. He was "playing with" some recoil formulas in one article I recall.

Ben_Rumson · Post by **Ben_Rumson** » Mon Oct 21, 2013 11:48 am

The whole"LOW PRESSURE" low bolt thrust thing hinges on how hard or soft the brass is and case taper...Edit: Or to be more precise, the elasticity of the cases brass.

FatJackDurham · Post by **FatJackDurham** » Mon Oct 21, 2013 4:42 pm

There is another consideration, as well. I dont know the physics term for it, but when two different metals are pressed against each other at high pressures, the friction can lock them in place temporarily. I believe this is the principle at work when firing certain automatics. The brass cartridge is pressed against the chamber and stuck in place until the pressure drops enough to allow the recoil to eject the cartridge. I think I read about it when reading about the 1911 design.

Anyway, a low pressure cartridge might not have enough side pressure to lock the cartridge in the chamber.

w30wcf · Post by **w30wcf** » Mon Oct 21, 2013 5:03 pm

It has been my observation that it is only the primer on low pressure cartridges that pushes against the bolt, so the pressure against the bolt is pretty low........

w30wcf

Sixgun · Post by **Sixgun** » Mon Oct 21, 2013 6:54 pm

w30wcf wrote:It has been my observation that it is only the primer on low pressure cartridges that pushes against the bolt, so the pressure against the bolt is pretty low........

w30wcf

Thank you Jack......#1 has spoken.------6

rimrock · Post by **rimrock** » Mon Oct 21, 2013 7:24 pm

w30wcf wrote:It has been my observation that it is only the primer on low pressure cartridges that pushes against the bolt, so the pressure against the bolt is pretty low........

w30wcf

I'm not arguing with you. No matter what phenomenon you call it, the most dead serious situation I personally faced was a strong lock up of a Ruger Vaquero with a very low pressure load. The barrel was too hot to touch for 3-4 minutes, because I have a free spin pawl I finally manged to back the cylinder around enough to get it unloaded, and the brass had to driven out with a wooden dowel. I lost all interest in any low pressure loads in any gun, and stay pretty much in the middle of mid range loads.

Griff · Post by **Griff** » Mon Oct 21, 2013 7:59 pm

Well... the experiment was a bust. Oh well.??? The part about being able to measure the headspace worked just like always... but, what I'd forgotten is that the Plasti-gage sticks to the bolt... not the case.

So... the headspace on my 1873 was .003"; the 1860 it was just shy of .003"; and on the Rossi 1892 it was also .003". But, it was kinda broke apart and trying to measure was not an easy proposition. I went ahead and fired the rounds... 12.9 grains of Blue Dot under a 253 grain JHP was no big deal. Didn't get to chrono them... as while I was checking the headspace... the wind blew over the tripod with the chronograph on it... Broke the tripod... so no load info.

So gosh, if it wasn't for some trigger time... it would've been a complete wash-out!

Sixgun · Post by **Sixgun** » Mon Oct 21, 2013 8:06 pm

Griff,
At least you shooting while you had the ag. I had it all day long at work and home.--6

KWK · Post by **KWK** » Mon Oct 21, 2013 8:26 pm

Sixgun wrote:John writes that lube loses it's properties after 10,000 psi and that it cannot set the case back after that level. Go and read it and see if I interpreted it correctly.

You read that correctly, but empirical evidence suggests it's not so. For generations the Brits measured case pressure by measuring breech thrust against a copper crusher. They found that if the case was not oiled, the indicated reading was off by another 25%; the oil makes a big difference.

The breech crushers bring up another problem with Barsness' argument: they worked on cartridges down to 30,000 psi, well below that at which he feels the brass takes all the breech load.

In his article, he says that protruding primers on his .25-35 rifle show the case didn't set back at those pressures. Perhaps, but there is another possible explanation. On his web site, Varmint Al has done some finite element analyses of the breech thrust problem. His results suggest the primer backs out at far lower pressures (as .30wcf noted above). This being the situation, it may be that during the blowdown after the bullet exits, the brass may relax well before the primer, allowing the primer to protrude even if the case pushed on the bolt; note this is my hunch, not Al's.

One fine bit of work cited in the article is that by Sisk using pressure sensitive film, although Barsness' summary of the results has me scratching my head. I plan to try these films in my .30-40 rolling block one day; I'm curious how much thrust there is. I wish I knew if and where Sisk has published his results.

Sixgun · Post by **Sixgun** » Mon Oct 21, 2013 8:56 pm

Thanks for the input KWK. I do remember reading in an old Lyman reloading manual something that you mentioned......depending on the pressure, sometimes the primer can back out and sometimes it will be reseated. I'm brain dead at the moment and will take a look see tomorrow.---6

earlmck · Post by **earlmck** » Mon Oct 21, 2013 11:04 pm

I keep thinking about this bolt thrust, brass grip, brass flow, etc. And I have another observation to throw into the pot to add to our confusion.

I have an old 25/20 with quite a lot of excess headspace. If I start with a piece of new brass and just load and fire with my old shootin' load of 11 grains of H4227 behind the 90 grain Lyman cast, In 5 or 6 shots the base will separate (the familiar symptom of excess headspace). This is well above the 14K of a true low-pressure load but is still a fairly low-pressure load (QuickLoad estimates about 25K psi). But if that case head wasn't stretching back against the bolt and then retracting after each firing, I wouldn't be getting that base separation, would I? (I neck-size only for loading this). And yes, the primers pooch out.

Maybe my experiment should be to see if I get base separations if I use a true low-pressure load . A second trial could be to see what effect lubing the case would have on the head separation. And if I had more nerve I might also see if firing a 60K psi load would cause the brass to flow to create a really good "fit" on the first firing and so avoid the base separation caused by repeated firings with excess headspace. Now if this was a Rossi or other new manufactured M92 I would try this 60K load, but this is an old 1900 era Winny (complete with black-powder sized firing pin). So I'm skipping that part of the experiment.

w30wcf · Post by **w30wcf** » Tue Oct 22, 2013 6:25 am

rimrock wrote:
w30wcf wrote:It has been my observation that it is only the primer on low pressure cartridges that pushes against the bolt, so the pressure against the bolt is pretty low........

w30wcf
I'm not arguing with you. No matter what phenomenon you call it, the most dead serious situation I personally faced was a strong lock up of a Ruger Vaquero with a very low pressure load. The barrel was too hot to touch for 3-4 minutes, because I have a free spin pawl I finally manged to back the cylinder around enough to get it unloaded, and the brass had to driven out with a wooden dowel. I lost all interest in any low pressure loads in any gun, and stay pretty much in the middle of mid range loads.

I have had the same thing happen using just the primer to fire a wax bullet(!). Opening the flash hole to 1/8" resolved that problem, I keep those case segregated for shooting wax or plastic bullets with just the primer so they don't get mixed in with cases used for standard loads.

w30wcf

w30wcf · Post by **w30wcf** » Tue Oct 22, 2013 6:35 am

earlmck wrote:I keep thinking about this bolt thrust, brass grip, brass flow, etc. And I have another observation to throw into the pot to add to our confusion.

I have an old 25/20 with quite a lot of excess headspace. If I start with a piece of new brass and just load and fire with my old shootin' load of 11 grains of H4227 behind the 90 grain Lyman cast, In 5 or 6 shots the base will separate (the familiar symptom of excess headspace). This is well above the 14K of a true low-pressure load but is still a fairly low-pressure load (QuickLoad estimates about 25K psi). But if that case head wasn't stretching back against the bolt and then retracting after each firing, I wouldn't be getting that base separation, would I? (I neck-size only for loading this). And yes, the primers pooch out.

earlmck.
As the yield strength of the brass is exceeded, it will stretch a bit with each successive firing (the amount depending of the pressure and amount of headspace) until the case finally separates if the headspace is too much for the load used.

If you were to expand the case necks to a larger caliber or use .32-20 brass and size it down to fit your rifle's headspace, all would be well.

w30wcf

Tycer · Post by **Tycer** » Tue Oct 22, 2013 6:56 am

Earl I look forward to your report. This has been a great thread. When working up top loads for my 360 Dan Wesson Win 94 the bolt would pop open if the case was not dry.

earlmck · Post by **earlmck** » Tue Oct 22, 2013 11:05 am

w30wcf wrote:earlmck.
As the yield strength of the brass is exceeded, it will stretch a bit with each successive firing (the amount depending of the pressure and amount of headspace) until the case finally separates if the headspace is too much for the load used.

If you were to expand the case necks to a larger caliber or use .32-20 brass and size it down to fit your rifle's headspace, all would be well.

Yes, I have used both of those techniques to "fix" the headspace. But my first try at fixing it was to "headspace" the case on the bullet, expecting the case to then expand to fit properly. This doesn't work with this rifle with the 25K psi load I have been using. The case, at 25K psi, apparently does not stay expanded, even though the case head was held firmly against the bolt on that first firing. I'm picturing this "mid-level" pressure as being an area where the case presses back against the bolt (thus imparting at least some "bolt thrust") but then springs back into its initial configuration. I'm thinking it must be pressing against the bolt on firing because it is this "spring out against the bolt and then shrink back to initial configuration" which works the brass (much like we bend wire a few times back and forth to break it at the bend) and causes the eventual head separation.

I also have an '06 with badly excess headspace. An initial firing and subsequent sizing which does not set back the shoulder works fine for this rifle and I have never experienced a head separation in this rifle. So I am thinking the brass is responding differently when put under 60K pressure vs. 25K pressure.

Anyway, that is the picture in my mind at present time, as a result of reading all the stuff generated in this thread and pondering my own experiences.

To be revised as further data becomes available.

Sixgun · Post by **Sixgun** » Tue Oct 22, 2013 2:14 pm

Earl,
Did you ever think that while you "fit" the case to your chamber that there might be play in the lock work that allows it to stretch even more.

Try this....with the lever up and the bolt against the breech, get a thin screwdriver and see if you can pry the bolt back a few thou.----6

earlmck · Post by **earlmck** » Tue Oct 22, 2013 10:43 pm

Sixgun wrote:Earl,
Did you ever think that while you "fit" the case to your chamber that there might be play in the lock work that allows it to stretch even more.

Try this....with the lever up and the bolt against the breech, get a thin screwdriver and see if you can pry the bolt back a few thou.----6

Hmmm.... Yep, with a normal (not headspace fixed) cartridge I can get a bit of play. Can't really see it but I can feel it. So what is this telling me? And have I somehow managed to hijack your nifty thread, Sixgun, and get off on my little headspace thing? I didn't want to do that!

KWK · Post by **KWK** » Tue Oct 22, 2013 10:48 pm

earlmck wrote:[... my first try at fixing it was to "headspace" the case on the bullet, expecting the case to then expand to fit properly. This doesn't work with this rifle with the 25K psi load I have been using.

Could it be as simple as the hammer strike followed by the primer blast -- especially the latter -- shoving the case forward, despite your bullet?

w30wcf · Post by **w30wcf** » Tue Oct 22, 2013 10:53 pm

Griff wrote:Well... the experiment was a bust. Oh well.??? The part about being able to measure the headspace worked just like always... but, what I'd forgotten is that the Plasti-gage sticks to the bolt... not the case.

So... the headspace on my 1873 was .003"; the 1860 it was just shy of .003"; and on the Rossi 1892 it was also .003". But, it was kinda broke apart and trying to measure was not an easy proposition. I went ahead and fired the rounds... 12.9 grains of Blue Dot under a 253 grain JHP was no big deal. Didn't get to chrono them... as while I was checking the headspace... the wind blew over the tripod with the chronograph on it... Broke the tripod... so no load info.

So gosh, if it wasn't for some trigger time... it would've been a complete wash-out!

Griff,
Thank you for the report. One way to increase headspace is to remove material from the front of the rim. If removed from the back of the case the primer pocket would likely need to be deepened, depending on the amount of the material removed.

I remember increasing the headspace on two .45 colt cases by doing that several years ago. I was testing 30,000 psi loads though and that was enough pressure to overcome the primer backout and the primers were seated flush after firing. I need to redo with a standard .45 Colt SAMMI spec load and see what happens.

w30wcf

w30wcf · Post by **w30wcf** » Tue Oct 22, 2013 11:01 pm

earlmck,
Regarding the headspace in your .25-20 -----when sizing down .32-20 cases or the expanded neck .25-20 brass, size it back just enough that you feel pressure in closing the lever toward the end of the travel. That will lock things up tighly.

Another option is to have a donut shaped shim of the proper thickness for 0 headspace made then place it over the case chamber and fire it. That will form the case to the proper dimension for your rifle. Also, if the firing pin protrudes enough a shim could be epoxied on the face of the bolt to take up the headspace or a shim could be epoxied to the face of the chamber.

w30wcf

Buck Elliott · Post by **Buck Elliott** » Tue Oct 22, 2013 11:15 pm

rimrock wrote:
w30wcf wrote:It has been my observation that it is only the primer on low pressure cartridges that pushes against the bolt, so the pressure against the bolt is pretty low........

w30wcf
I'm not arguing with you. No matter what phenomenon you call it, the most dead serious situation I personally faced was a strong lock up of a Ruger Vaquero with a very low pressure load. The barrel was too hot to touch for 3-4 minutes, because I have a free spin pawl I finally manged to back the cylinder around enough to get it unloaded, and the brass had to driven out with a wooden dowel. I lost all interest in any low pressure loads in any gun, and stay pretty much in the middle of mid range loads.

None of what you describe here indicates a "low pressure" load, regardless of your intent when you loaded the cartridge..

Gentlemen: seldom have I seen so much unadulterated hogwash spread about on Any subject discussed on this forum..

"Bolt thrust" is a very real factor, and is directly proportional to the gas pressure generated and the area of the case head supported by the bolt or standing breech.. Harnessing that thrust (pressure, if you will..) is what makes "blowback" or short recoil operated mechanisms work the way they do..

It's been a long time since I read Ackley's treatise on the strength of various actions or action types, but nowhere do I recall his holding a Winchester '94 bolt closed by "thumb pressure" on the rear of the bolt, although he did fire such a gun with the locking lug removed.

It is important to visualize a cartridge case as a Gasket, which contains and directs the force of combustion gases.. If everything works as it should, the case expands against the chamber wallls, forming a momentary gas seal, at least until the "piston" or bullet, in this case, has started to move down the bore,ahead of the pressure..

It has been mentioned that most rifle and pistol bolts (or slides) are fairly massive, having a lot of inertia to overcome before they move appreciably.. Remember that the "bolt" in a '66 or '73 Winchester is a small, lightweight piece of steel, not supported directly in the receiver. The fairly large hammer and its spring provide some backup on firing, but the main load is taken by the links and pins and their attachment to the receiver..

If Bolt Thrust were not a major factor, I would have built my .454 rifle on a '73-style action, instead of engineering a smaller version of the '86, with its perpendicular locking lugs.. The angled locking geometry of the '92 or '94 Winchester (or any of the Marlins) is not completely adequate to contain the pressure and the "thrust.." I know.. I wrecked a pile of them, proving the point..

Nate Kiowa Jones · Post by **Nate Kiowa Jones** » Wed Oct 23, 2013 12:35 am

Buck Elliott wrote:
rimrock wrote:
w30wcf wrote:It has been my observation that it is only the primer on low pressure cartridges that pushes against the bolt, so the pressure against the bolt is pretty low........

w30wcf
I'm not arguing with you. No matter what phenomenon you call it, the most dead serious situation I personally faced was a strong lock up of a Ruger Vaquero with a very low pressure load. The barrel was too hot to touch for 3-4 minutes, because I have a free spin pawl I finally manged to back the cylinder around enough to get it unloaded, and the brass had to driven out with a wooden dowel. I lost all interest in any low pressure loads in any gun, and stay pretty much in the middle of mid range loads.
None of what you describe here indicates a "low pressure" load, regardless of your intent when you loaded the cartridge..

Gentlemen: seldom have I seen so much unadulterated hogwash spread about on Any subject discussed on this forum..

"Bolt thrust" is a very real factor, and is directly proportional to the gas pressure generated and the area of the case head supported by the bolt or standing breech.. Harnessing that thrust (pressure, if you will..) is what makes "blowback" or short recoil operated mechanisms work the way they do..

It's been a long time since I read Ackley's treatise on the strength of various actions or action types, but nowhere do I recall his holding a Winchester '94 bolt closed by "thumb pressure" on the rear of the bolt, although he did fire such a gun with the locking lug removed.

It is important to visualize a cartridge case as a Gasket, which contains and directs the force of combustion gases.. If everything works as it should, the case expands against the chamber wallls, forming a momentary gas seal, at least until the "piston" or bullet, in this case, has started to move down the bore,ahead of the pressure..

It has been mentioned that most rifle and pistol bolts (or slides) are fairly massive, having a lot of inertia to overcome before they move appreciably.. Remember that the "bolt" in a '66 or '73 Winchester is a small, lightweight piece of steel, not supported directly in the receiver. The fairly large hammer and its spring provide some backup on firing, but the main load is taken by the links and pins and their attachment to the receiver..

If Bolt Thrust were not a major factor, I would have built my .454 rifle on a '73-style action, instead of engineering a smaller version of the '86, with its perpendicular locking lugs.. The angled locking geometry of the '92 or '94 Winchester (or any of the Marlins) is not completely adequate to contain the pressure and the "thrust.." I know.. I wrecked a pile of them, proving the point..

+1

There is always bolt thrust. Even at low pressures. What do you think rips the heads off cases when you have excessive headspace.
Buck, thanks for taking the time to post. I have been to this topic 6 or 7 times scratching my head thinking I should post something but you summed it up well.

.45colt · Post by **.45colt** » Wed Oct 23, 2013 4:21 am

Well I better get some popcorn at the store today........................................................

.

buckeyeshooter · Post by **buckeyeshooter** » Wed Oct 23, 2013 5:17 am

.45colt wrote:Well I better get some popcorn at the store today........................................................ .

Well for me. If Nate Kiowa Jones agrees with Buck Elliot, I don't need popcorn cause the question is answered! Are you hungry for popcorn perhaps?

w30wcf · Post by **w30wcf** » Wed Oct 23, 2013 5:36 am

Gentlemen, I respect your opinions, but since a ballistician who worked many years for one of the powder companies in a lengthy conversation with me on this very same subject many years ago, indicated that there is much less pressure on the bolt in low pressure cartridges than is calculated mathematically.

It was his opinion that the amount would be dependent on the fit of the cartridge in the chamber, the length of the cartridge, yield strength of the cartridge material, and so on. Thus, I would think that the .45 Colt would typically have more bolt trust than say a .44-40 at the same pressure since there is more windage in the chamber in a .45 Colt than the .44-40 and the brass is thicker. A .38-55 cartridge would have less bolt trust than a .38 Special due to its body length at the same chamber pressure.

If the cartridge is not being at least partially locked in the chamber, which reduces the amount of bolt thrust on low pressure cartridges, why does the primer take up the headspace when there is much less pressure on the primer?

Now on the other hand the .454 is a horse of a completely different color! There is plenty of bolt thrust due to the much higher pressure it generates........

Sincerely,
w30wcf

Sixgun · Post by **Sixgun** » Wed Oct 23, 2013 4:38 pm

Well, I just went outside and made a video and shot one of my first variation Colt Lightnings in 44-40. This rifle has no action lock except a little lever in the front that you use while hunting. This was pushed forward and by doing so, allowed the action to cycle freely. I fired 2 shots with 6 gr. of Bullseye and a 200 gr. Hensley & Gibbs bullet. (In the video, I said a 170 gr. Lyman...its been a long day)

The bolt did not even come back far enough to put the hammer on the safety notch.

Remember..................this was a low pressure load, probably 15K

So...............I go to You Tube to upload it and a little sign pops up that says my "computer has stopped working" So...........I go to firefox and try it again and this time I get a message that says "it will take 595 minutes to download it".

Im really aggravated now and for now, you folks will just have to believe me.

----Sixgun

Griff · Post by **Griff** » Wed Oct 23, 2013 6:15 pm

Buck, first of all, thanks for your input. And you're right... I certainly don't KNOW about bolt thrust... and I've heard lots of theories. One of which, IIRC, is that bottleneck cartridges generate more bolt thrust than a straight wall cartridge in the same pressure range. Again, assuming that both cartridges have the same chamber to cartridge fit.

Much of this I've not paid any attention to since I started cowboy shootin'. And today, paid for it. Loaded up some 5.56NATO last night for hole punchin' today with the new AR build. Could only get 2 or 3 rounds out of 50 to chamber in either my son's Colt Competition or mine. BUT, they would chamber in my Windham Weap. SRC! At 100 yards that little Windham carbine would hold 'em inside 2". Flakey 1-4x24 scope has the adjustment knobs marked just the opposite of what you need to actually adjust the POI... what a PIA! At least it holds zero! Coyotes gonna be toast! Stainless barrel on the new AR still needs some "conditioning"! Teases me with a great ½" 3-shot group, then throws two flyers... Grrr. Back to cleaning and polishing. Which I understand is necessary with Stainless. My Remington 700 wasn't like this... seemed to shoot better'n the carbon steel version right out of the box... but maybe they prepare their custom rifles a little better than a "parts place"?

Maybe the next time I'm home I'll do some more tinker'n with my experiment and get some bone-fide repeatable results. 10 days or so hence.

Six, frustrating, ain't it?