Cast bullets: bore size or throat size?

[Walt]

There have been changing discussions around how large to size cast bullets for best accuracy. Years ago it was recommended to size bullets to match groove diameter. In the past two or three decades however, the consesus has been to size bullets close to the diameter of the chamber throats, preferably a fit so close that sized bullets can be pushed through throats with a small amount of resistance.

From Ken Waters' PET LOADS in his testing of the .44 Special he stated that one of his test guns was a (relatively) recent production SAA with chamber throats of .432" and groove diameter of .427". I consider Ken Waters to have been a thoughtful and careful experimenter; based upon recent thought, he did a lot of his cast bullet sizing for the Colt at .432" to match throat diameter but found that when he reduced his bullets to .427" it cut his group size in half.

Without a doubt, each gun is a law unto itself.

[Twodot]

that last sentence says it all
..

[Rockrat]

I had a Colt NF in 44 spcl with pretty well, the same chamber mouth and groove dimensions. .427" leaded the bore, .429" wasn't much better, .430" was a bit better, then .431" was an improvement, .432" was pretty good and .433" was the best and I stopped there.

[Scott Tschirhart]

Agreed. Experimentation can lead you to combinations that don’t make sense.

[samsi]

Assuming proper relationship of bore and throat size, my take is that it's more important to be close to throat size. It's of lesser importance with bullets of longer bearing surface that seat further out of the case to where the bullet has started into the forcing cone before clearing the case entirely (reduces tipping with under throat size bullets). I believe it's likely that's the reason that Elmer got satisfactory results with his bullet sized to groove diameter or .001 over. I have no idea what the throats were on his custom guns but the S&W's likely weren't throated very tight.

[Walt]

Yeah, Elmer said that was the reason he designed the original Lyman 429421 with a full-width front band. I also suspect he was correct in his design of a square-bottomed grease groove putting more lube into the rifling due to hydraulic effect from an obturating bullet collapsing the grease groove.

[Gobblerforge]

I had a Colt NF in 44 spcl with pretty well, the same chamber mouth and groove dimensions. .427" leaded the bore, .429" wasn't much better, .430" was a bit better, then .431" was an improvement, .432" was pretty good and .433" was the best and I stopped there.

Do I understand that you bought 6 different molds to try this? If so that is a serious investment into finding accuracy. What do you do with the other molds you don't use?

[Tycer]

I had a Colt NF in 44 spcl with pretty well, the same chamber mouth and groove dimensions. .427" leaded the bore, .429" wasn't much better, .430" was a bit better, then .431" was an improvement, .432" was pretty good and .433" was the best and I stopped there.

Do I understand that you bought 6 different molds to try this? If so that is a serious investment into finding accuracy. What do you do with the other molds you don't use?

I read that as sizing dies. Or he opened one up.

[marlinman93]

.001" over groove diameter has always worked best for my rifles. Shooting throat diameter can result in swaging down bullets as they enter the bore, and that lead has to go somewhere. Where it goes is the base of the bullet, which can lead to "fins" hanging off the base created by the lands and grooves. Anything that changes the base of the bullets will affect accuracy and not for the better.

[Griff]

.001-.002" over groove diameter has always been the rule of thumb I followed. I get a bit anxious going bigger than that with pressures, etc.

[piller]

I only have 1 revolver I shoot lead bullets from. A Ruger Blackhawk with 2 cylinders. .45 Colt and 45 ACP. I buy the lead bullets sized to .452 and accuracy has been good. Funny, but the 45 ACP has been accurate as anything I can shoot with the .451 jacketed bullets. I have never measured the cylinder throats or the forcing cone. Since it can get down to an inch at 25 yards when I have a rest and am taking my time, there doesn't seem to be any reason to change anything. Freehand, my groups are about 2 or 3 inches. More than 2 cups of coffee that day opens the group up.

[Scott Tschirhart]

I only have 1 revolver I shoot lead bullets from. A Ruger Blackhawk with 2 cylinders. .45 Colt and 45 ACP. I buy the lead bullets sized to .452 and accuracy has been good. Funny, but the 45 ACP has been accurate as anything I can shoot with the .451 jacketed bullets. I have never measured the cylinder throats or the forcing cone. Since it can get down to an inch at 25 yards when I have a rest and am taking my time, there doesn't seem to be any reason to change anything. Freehand, my groups are about 2 or 3 inches. More than 2 cups of coffee that day opens the group up.

Don’t fix what ain’t broke!

I’m shooting really soft .454 bullets in my .45 Colts for my everyday loads. My 270SAA bullets are sized to .453. I generally like my throats to measure .4525. But I haven’t even measured this one because it shoots so good.

In my .44 Special I’m shooting .430s

[Rimfire McNutjob]

Glad I caught this before it rolled off of the page. Just ordered my first SAA in .45 and now I'm getting a set of pin gauges in .451- to .455- to measure the chamber throats. I managed to order some commercial ammo for my first outing but the stuff is hard to find in the bullet I want. Once I have the brass, I'll order some commercial cast based on what the pin gauges say for the throats and see how they run.

[Walt]

McNutJob, the commercial caster I have used for years for anything I don't cast myself is SNS Casting. Their bullets are fairly hard; their .45 Colt bullets are sized at .452 and look great. They are available in SWC, RNFP or coated. I normally buy 1000 250 gr RNFP at a time but boxes of 500 are available as well. They have 2 day shipping and their flat rate fee is $15 last I saw. The best thing is their packaging. They use carpet padding around their boxes to protect the bullets and I have never seen any dented or deformed bullets.

[piller]

Walt, they sound good. I will look them up.

[piller]

They list BHN of 16-17. Sounds reasonable to me, but I freely admit to not being any sort of expert on this subject.

[Rimfire McNutjob]

McNutJob, the commercial caster I have used for years for anything I don't cast myself is SNS Casting.

Wow, that seems pretty cheap for a 500ct box in 45LC. I've not really read anything on the use or performance of coated bullets.

[AJMD429]

…Since it can get down to an inch at 25 yards when I have a rest and am taking my time, there doesn't seem to be any reason to change anything. Freehand, my groups are about 2 or 3 inches. More than 2 cups of coffee that day opens the group up.

Wow I’d not mess with perfection either…!

The 45 ACPs in my 45 Colt RedHawk are TERRIBLE but I’ve not measured anything, and I have to admit the 45 Colt so far all is factory load ‘Cowboy’ or Buffalo Bore and they both do well but the 45 ACP is so far all old bulk commercial reloads. So that’s likely part of the difference.

[flightsimmer]

I have a 4-3/4" EMF Hartford in 45 Colt caliber.
I feel like it is perfection of the breed in every way.
I don't remember the exact specifications now but the cylinder throats were much larger than the grove in the barrel.

It bothered me enough for me to try to locate a cylinder with smaller throat sizes, I was never able to but it didn't seem to matter because it shot to middle of beer-can at 25 yards with a 6 o'clock hold and dead-on at 50 yards.

So I just accepted it as it was and learned to love it.

[Scott Tschirhart]

Yes, don’t fix what ain’t broke!