How much does drass type affect velocity & psi?

[ReaperDriver]

I know that different brass types affects velocities and pressures due to differences in internal volume. But HOW MUCH quantitatively are we talking about in a .308?

The reason I ask is because I'm doing load workups in my once fired (by me) FC and Rem brass because that's what I have the most of and I'm trying to keep as many variables constant as possible. I have some WIN and Black Hills brass - but not enough of any one type to get me through a good workup test at the range. If I get satisfactory results in the FC brass with a particular load but then switch to WIN, BH or eventually Lapua brass - how much is that going to change the equation? And if I switch to a different brass, will I have to do an entire new set of load workups again to find my sweet spot?

 

[MitchAlsup]

Re: How much does drass type affect velocity & psi?

Many tactical loads are developed at the edge of sane pressures. It is (great understatement) unwise to transfer a maxed-out load to a different case without dropping back and redeveloping the load.

Given the amount of data available with Win, Lapua brass some general rules have been 'observed'. That is: take a load developed for a Win 308 case and a drop between 0.3gr to 0.4gr is where you will find similar pressures and MV from the Lapua cases. But EVEN IN THIS CASE the only WISE thing to do is to drop by at least a couple of percent and work back up watching pressure signs on the way up. {This also assumes that the cases are prepaired in the same ways--primer pocket, flash hole debur, size, debur, chamfer, tumble,...}

In my load developments in 308, I have done a few Fed cases (From FGMM). I find these are almost identical in charge weight to the charge weight I generally use in Win cases. The black Hills brass I got was uniformly Win cases.

 

[fockell]

Re: How much does drass type affect velocity & psi?

I would say it could effect your pressure by as much as 15% and your velocity by as much as 5%. Depending on how close you are to a max load. Currently I am using BH brass in my 308. I am running 47.9gr of RL15 and a 155grn bullet. If I tried running that in a remington case it is likely it blow the primer out or have some super sticky bolt lift. If i could even fit that much powder in the case. I think you will be okay to start out with a lower case capacity brass like FED/REM and move to Lapua, Win, BH and have no troubles at all. Especially if you are running a compressed load. Worst you may have to do is add a bit of powder. --brandon

 

[Goin'Hot]

Re: How much does drass type affect velocity & psi?

Published data for 155's using IMR4895 shows a max of 47.5 gr compressed. Using LC brass and Nosler 155 gr CC, I load 44.1 gr and have sharp primers where the firing pin hits. I pierce primers at 44.5 gr. My LR308 REALLY likes this load and it's temperature safe in MY gun.

Published data shows a velocity of 2897 where I see 2815. My load is not compressed however. You always read to work up a load up slowly and approach max cautiously and by my #'s you can see why.

These are not typical results in my experience but, they are certianly worth making reference to.

I do not see these pressure signs in FC brass but I have 1000 pcs of LC. I recommend sticking with one headstamp.

 

[jrob300]

Re: How much does drass type affect velocity & psi?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Goin'Hot</div><div class="ubbcode-body">I recommend sticking with one headstamp. </div></div>

+1

Start saving your pennies and buy up a bunch at once from the same lot. Saves many headaches (and a lot less plastic shoes boxes

)

John

 

[GOING FOR 2000]

Re: How much does drass type affect velocity & psi?

It all has to do with case volume, which affects pressure and velocity.

If you are serious go ahead and buy Lapua cases and stay with them, they are the most consitent I have found.

Use the others for break in and fouling shots.

 

[Mc85]

Re: How much does drass type affect velocity & psi?

using the same powderload, same bullets, same seating depth Loaded at the same time, and shot at the same basic time (one after the other) a five shot group when using win cases gave me 100fps slower than the same load using nosler brass.....

hope that gives u an idea of the extremes that can be seen.

 

[ReaperDriver]

Re: How much does drass type affect velocity & psi?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Mc</div><div class="ubbcode-body">using the same powderload, same bullets, same seating depth Loaded at the same time, and shot at the same basic time (one after the other) a five shot group when using win cases gave me 100fps slower than the same load using nosler brass.....

hope that gives u an idea of the extremes that can be seen. </div></div>

Mmmm, thanks. I wonder if that accounts for why I'm seeing such slow velocities than expected with my FC brass?

 

[jrob300]

Re: How much does drass type affect velocity & psi?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Mc</div><div class="ubbcode-body">using the same powderload, same bullets, same seating depth Loaded at the same time, and shot at the same basic time (one after the other) a five shot group when using win cases gave me 100fps slower than the same load using nosler brass....</div></div>

I load for a 300WM, but I have seen the same thing. I fill a case with a very fine powder (like TAC) to check case capacity. Full case in Nosler barely comes past the bottom of the neck on Win. This is a very visual way of demonstrating case volume differences.

John

 

[ReaperDriver]

Re: How much does drass type affect velocity & psi?

So is it safe to say that brass with higher volume is going to have lower pressures and velocities with the same powder charge - all other things being equal?

 

[Greg Langelius *]

Re: How much does drass type affect velocity & psi?

I would say that results would be difficult to predict. That reason, in itself, is enough reason to treat different brass as separate issues. When running loads that are at or near limits, this becomes a far more critical issue.

Basic handloading rule. Changing components requires load workup and confirmation. Never ignore this rule.

Greg

 

[ReaperDriver]

Re: How much does drass type affect velocity & psi?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Greg Langelius *</div><div class="ubbcode-body">I would say that results would be difficult to predict. That reason, in itself, is enough reason to treat different brass as separate issues. When running loads that are at or near limits, this becomes a far more critical issue.

Basic handloading rule. Changing components requires load workup and confirmation. Never ignore this rule.

Greg </div></div>
Thanks. good words to live by. I was just wondering, in general, what to expect as I start the work up process again.

When I get my batch of Lapua brass in, I won't have to worry about this.

 

[jrob300]

Re: How much does drass type affect velocity & psi?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ReaperDriver</div><div class="ubbcode-body">So is it safe to say that brass with higher volume is going to have lower pressures and velocities with the same powder charge - all other things being equal? </div></div>
Theoretically from an interior ballistics standpoint, yes. But because there are so many variables involved and the results of a miscalculation are potentially life-threatening, Greg's advice is the prevailing rule of reloading.

I've talked at length with some of the ballistics guys at different bullet and powder companies and ALWAYS at the end of the conversation they remind me, start low and build up slowly. Not only is this safe, but you become more knowlegable about how different components perform in your gun under a known set of conditions (p.s. write EVERYTHING down

).

John

 

[jrob300]

Re: How much does drass type affect velocity & psi?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: jrob300</div><div class="ubbcode-body">I fill a case with a very fine powder (like TAC) to check case capacity. Full case in Nosler barely comes past the bottom of the neck on Win. This is a very visual way of demonstrating case volume differences.</div></div>

Just to clarify, I use this method to determine relative case capacity only, not to predict results. We weigh our brass to do the same thing, but then work up a new load. I just like to know what I'm truly working with.

John

 

[ReaperDriver]

Re: How much does drass type affect velocity & psi?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: jrob300</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ReaperDriver</div><div class="ubbcode-body">So is it safe to say that brass with higher volume is going to have lower pressures and velocities with the same powder charge - all other things being equal? </div></div>
Theoretically from an interior ballistics standpoint, yes. But because there are so many variables involved and the results of a miscalculation are potentially life-threatening, Greg's advice is the prevailing rule of reloading.

I've talked at length with some of the ballistics guys at different bullet and powder companies and ALWAYS at the end of the conversation they remind me, start low and build up slowly. Not only is this safe, but you become more knowlegable about how different components perform in your gun under a known set of conditions (p.s. write EVERYTHING down

).

John </div></div>
John, message received loud and clear! Thanks!