45-70 IMR3031 load headscratcher

otteray · Post by **otteray** » Thu Dec 27, 2007 4:49 pm

My head is starting to bleed, from scratching it, while trying to figure this out:

45-70 Marlin Guide Gun w/ ported 6 groove barrel

Old West 350 gr. gas check cast Wheel Wt (365gr actual total wt); then
sized .459 w/alox lube

RP brass trimmed to 2.095

Fed 210 Rifle Primers (seated .006"- .008" deep)

All loads seated to OAL 2.510-15" (in top groove)

Lee dies, Lee Factory Crimp die
__________________________________________________________

5 shot groups @ 100 yards, Lyman peep sight, from benchrest:

45 gr
1320 fps ave. 1366 hi - 1275 low) 3" group

46gr
1411 fps ave. (1424 hi - 1400 low) 2" group

47gr
1479 fps ave. (1478 hi - 1456 low) 1" group

48gr
1470 fps ave. (1485 hi - 1462 low) 2" group

How could the velocities be so close ( average of 9 fps difference with 47 and 48 grains) and yet the groups be twice as big using one more grain?
I'm sure of the powder weights, by the way.
Please help me heal my head scratching wounds!!
Ray

cutter · Post by **cutter** » Thu Dec 27, 2007 4:54 pm

A two inch average group size isn't anything to sneeze at...

Fouling?

Leverluver · Post by **Leverluver** » Thu Dec 27, 2007 5:15 pm

Harmonics dude, harmonics. Every barrel has a point in it's vibration range (like a bell or tuning fork) where it is swinging through a smaller or more predictable arc than at another point.

Besides, unless you shot at least 5 (better 10) groups of each load and took an average, I wouldn't put that much stock in the difference between the 1" and 2" groups. If it does it consistently, you've really got something there. If it doesn't, you have random statistical noise.

Thunder50 · Post by **Thunder50** » Thu Dec 27, 2007 5:23 pm

I believe that the results you show , is when you have reached a max efficiency load. You get diminishing returns with more powder and quite often, groups open up. You might not be at max load, but you are probably getting close to it.

otteray · Post by **otteray** » Thu Dec 27, 2007 5:23 pm

cutter wrote:A two inch average group size isn't anything to sneeze at...

Fouling?

The barrel had been cleaned before firing.
I fired one fouling shot before the actual chronographing.
But my point is, why such a differerence of group size with similar velocities, when using one grain more of powder?
By the 3rd and 4th group, the barrel had been adequately fouled

otteray · Post by **otteray** » Thu Dec 27, 2007 5:30 pm

levergunlover and thunder50, I think you on to something!

I do think cutter has a point about fouling , too. Too clean a bore may not be a good thing....

KirkD · Post by **KirkD** » Thu Dec 27, 2007 5:49 pm

What Leverluver said. You especially have to take an adequate sampling. You may find that if you shot five 5-shot groups at each loading, they may all average out to the same group size per load. In other words, you are seeing variations about a mean for that load range. Harmonics can also play a part but, again, you will need a greater sampling for each load to get a feel for that.

otteray · Post by **otteray** » Thu Dec 27, 2007 6:03 pm

KirkD wrote:What Leverluver said. You especially have to take an adequate sampling. You may find that if you shot five 5-shot groups at each loading, they may all average out to the same group size per load. In other words, you are seeing variations about a mean for that load range. Harmonics can also play a part but, again, you will need a greater sampling for each load to get a feel for that.

Guess I now have a good excuse to load up a bunch more, instead of mowing the lawn. Thanks!

Win94 · Post by **Win94** » Thu Dec 27, 2007 6:07 pm

..............Lawn in December????

jdad · Post by **jdad** » Thu Dec 27, 2007 6:07 pm

The most accurate load I had, when I owned my 1895 Cowboy, was 47gr of 3031 under a 300 gr Laser Cast. 42gr was almost as accurate.

Bramble · Post by **Bramble** » Thu Dec 27, 2007 6:34 pm

The answer may be that having reached all of the powder that can be burnt in the barrel at 47 grains then the extra is being burnt outside of the barrel as the bullet exits the muzzle thus upseting the bullet slightly given that the velocity of the expelled gas is substancially higher than the bullet.

Regards

1886 · Post by **1886** » Thu Dec 27, 2007 7:19 pm

The guys covered it very well. It is not uncommon for velocity to actually decrease as powder charges increase to a point.... No need to state the obvious but I think your third load is probably the one. 1886.

Paul105 · Post by **Paul105** » Thu Dec 27, 2007 7:38 pm

KirkD nailed it. Shoot 5, 5 shot groups and see what happens. The results could easily be reversed and most assuredly will be different. One 5 shot group isn't statistically relevant.

Looks like you have a very accurate rifle, and the operator ain't too shabby either.

Just think how much more shooting you get to do trying to figure out the answer.

Paul

45-70marlin · Post by **45-70marlin** » Thu Dec 27, 2007 7:43 pm

Otteray, did you let the barrel cool after each shot? If your barrel heats up your group will open up.

otteray · Post by **otteray** » Thu Dec 27, 2007 8:35 pm

45-70marlin wrote:Otteray, did you let the barrel cool after each shot? If your barrel heats up your group will open up.

Yep; about a minute between each shot.
I will make a bunch more loads, and try them out using 46, 47 and 48 grains using KirkD's method.
Next weekend, I guess, since it's supposed to rain for the next few days here.

Post by **Old Savage** » Thu Dec 27, 2007 9:53 pm

48 gr may be a little beyond its best pressure or it may have a less consistent pressure when the bullet exits the muzzle but I agree you need more shooting to decide if the 47 gr load is really better.

otteray · Post by **otteray** » Thu Dec 27, 2007 11:46 pm

Old Savage wrote:48 gr may be a little beyond its best pressure or it may have a less consistent pressure when the bullet exits the muzzle but I agree you need more shooting to decide if the 47 gr load is really better.

So asumming you also agree with what Bramble said about upsetting (obturation,) you think I may need to harden the bullet for the 48gr load?
I may add some lino or heat treat for that load or more and try it.
BTW, it's .002 oversized.
Hmmm, so many reasons not to have time to mow the lawn...

Post by **Old Savage** » Fri Dec 28, 2007 12:05 am

We are always working with a variety of varibles we cannot measure and looking for what works in our rifles with our methods. Guns are different and methods are different. Can't tell if your solution would address the issue for sure take what works. I have seen some odd stuff but collect good loads for MY rifles. Shoot some more and see if 1" to 2" is you or the load.

Retro · Post by **Retro** » Fri Dec 28, 2007 12:09 am

otteray wrote: 47gr
1479 fps ave. (1478 hi - 1456 low) 1" group

I smell a typo.

But as others have said, when you get a small increase in velocity for a large increase in powder (in other words, when the curve starts flattening), you're at max, back off a bit.

I'd engrave "47 grains 3031" on the side of the rifle (OK, OK, I'm joking! :-)

otteray · Post by **otteray** » Fri Dec 28, 2007 11:26 am

Retro wrote:
otteray wrote: 47gr
1479 fps ave. (1478 hi - 1456 low) 1" group
I smell a typo.

But as others have said, when you get a small increase in velocity for a large increase in powder (in other words, when the curve starts flattening), you're at max, back off a bit.

I'd engrave "47 grains 3031" on the side of the rifle (OK, OK, I'm joking!

Yep; it should read:
1496 hi - 1456 lo

45-70 IMR3031 load headscratcher

45-70 IMR3031 load headscratcher

Re: 45-70 IMR3031 load headscratcher

Re: 45-70 IMR3031 load headscratcher