Home Forums Reloading Big Game Rifles A reloading question about the difference in barrel length velocity

I have a question for all of you other reloaders out there. In going over my 45/70 notes I noticed something very strange. I got two different velocities out of a 24� barrel and an 18.5� barrel. I know you are going to say that is what is supposed to happen but not this way, I say.

Marlin 24� barrel loaded with 300 gr. Bullet, WW brass, CCI primer, and H322 velocity ave. of 2014 fps.
Marlin 18.5� barrel with same load � 1891 fps a difference of 123 fps.

Now I change only the case and the primer to Starline and federal 215 and this is what I get:

24� � 2152 fps and the 18.5� 2089 fps only a difference of 63 fps

I go to a 405 gr. Woodledge and load one batch with WW and CCI and my velocity ave. is 1639 fps in the 24� and 1508 fps in the 18.5� barrel for a difference of 131 fps.

Ok now same bullet, same powder, but Starline case and federal 215 primers and I get a velocity ave. of 1787 fps out of the 24� and 1736 fps out of the 18.5� for a difference of only 51 fps.

All of these loads were loaded on the same day; 5 shots per load, and shot a week later all on the same day. The only thing I can figure is that the Federal primer is burning the powder much better but at the time I didn�t notice any unburned powder. As a side note both loads are starter loads for this powder and bullet weight. Have any of you seen this sort of difference before and/or do you have any idea what might have caused it?

At first glance, I don't see anything out of the ordinary with your data. Each sample you take is going to have normal random variation. I don't see any evidence that anything other than random variation is at work here.

Then you don't think that an average 130 fps difference with one case/primer versus a difference of only 60 fps average with a different case/primer is just random over 40 shots. I'm certainly not saying you are wrong but its strange, to me, that the randomness is so consistent. In that it isn't random, do you think?

I mean I expected the 130 fps difference between barrel lengths but only a 50/60 fps with only a primer/case change going from 24" down to 18.5" is cutting it in half.?

From reading your post, I see a pattern that indicates more of a velocity spread when using WW brass and CCI primers.

For example--WW Brass and CCI Primer and 24" barrel=2014 FPS.
WW Brass and CCI Primer and 18.5" barrel=1891 FPS.
Difference of 123 FPS.

Starline brass and Fed. Primer and 24" barrel=2152 FPS.
Starline brass and Fed. Primer and 18.5" barrel=2089 FPS.
Difference of 63 FPS.

The other examples follow the same pattern, i.e., higher velocity and less variation using Starline brass and Fed. Pri.

I can see two possibilities for the variation:

One: The Starline brass has less capacity than the WW brass, resulting in higher pressure and corresponding higher velocity.

Two: CCI and Fed. primer might have (probably do) different temperatures and/or strength, causing a variation in burning rate of the powder. The Fed. primer, along with the reduced capacity of the Starline brass, might further increase pressure, causing the powder to burn more efficiently in both barrel lengths.

The difference in the strength of the primer, coupled with the different in case capacity is probably the cause. I say this because the differences in the two loads is constant, and not erratic. The Fed. primer seems to be igniting the powder differently, therefore the higher velocity in both barrel lengths.

Even though the Fed. primer might be igniting the powder more efficiently, I doubt that you would see any more or less unburned powder when using the CCI primer.

Some primers work differently that others. I am not sure which is which, but some primers shoot hot particles into the powder, igniting the powder. Other primers shoot hot gases through the flash hole, igniting the powder in this manner. Others have both hotter gases and particles.

My guess is that the variation you see is caused by both the combination of the difference in case capacity and difference in strength, or method of ignition, of the two primers.

You could switch around even more, substituting the Fed. primer in the WW brass, and vice versa, and see if a pattern developes. You could also try Rem. Primers and possibly get entirely different results and a different pattern.

Thanks 1234567 Thinking about this over the last few days I've come to a simular conclusion about the Federal primers. Am going to load up the WW cases with Fed primers and the Starline cases with CCI primers and see what happens and will post my findings. This won't be until just before Hunting season here in Ga. because I also want to be closer to the same temp. that I shot at last time. Don't want to have any more variables than necessary. Thany you all for your time esp. 1234567.

Proof again as to why we handload...to get the most out of our rifles/components.

Starline cartridges are typically of stouter construction than Winchester, with slightly less powder capacity in Starline. All else being equal, one should get slightly higher pressures from Starline, and maybe slightly more velocity. The BPCR shooters always suggest one anneal Starline before the initial firing to prevent blowback. Being thicker and stiffer, it takes more umph to get them to seal against the chamber walls. Those using Winchester brass put much less emphasis on annealing. Given those issues, your results are about what I would expect. Be happy. Don't worry. 1Minute

Thank you I will. If it truly works out to be that the Fed primer combined with either case will consistently give me a loss of only 10-12 fps per inch plus maintain accuracy between my Limited 24"er and my GS 18.5"er I'll be as happy as a pig in a waller!!

In rereading my post, I did not intend to infer that one should anneal his Starline brass for use in smokeless units. Black powder does not generate as much pressure as smokeless, so it's only an issue in the BPCR circles.

I just recently loaded up some 400 grain slugs for my Marlin 45-70. Factory fodder shoots quite well, and I looking forward to maybe doing a dark timber elk with it this fall. A keen eyed critter can probably jump out of the way at 100 yards, but it's sure a fun unit to shoot. I bet it hits like a brick. 1Minute