My brass test

[lugerstew]

Went to the range yesterday and did two different loads for the brass test.
It kind of went the way I expected, with brass having less volume showing higher pressures/velocity.
I was shooting my Smith and Wesson M&P 10 308, 100 yds, 25 deg day, all brass was trimmed to same length with a CCI LR primer.

Test 1 Imr 4064 42.5g, coal=2.800 5 rounds each Nosler 168g CC HPBT
Hornady TAP 308 brass 191g=2595 avg. fps.,sd3
GFL 308 brass 191g=2605 avg. fps., sd10
PMC 308 brass 183g=2573 avg. fps., sd18
AP18 7.62x51 brass 181g=2545 avg fps.,sd23
PPU 308 brass 178g=2536 avg. fps., sd23

Test 2 Varget 43.5g, coal=2.800 10 rounds ea. Nosler 168g CC HPBT
Hornady TAP 308 brass 191g-2662 avg. fps., sd16
PMC 308 brass 183g=2622 avg. fps., sd11
AP18 7.62x51 brass 181g=2598 avg. fps sd12
WCC 308 brass 180g=2603 avg. fps sd8
MEN16 7.62x51 brass 180g=2594 avg. fps., sd23

I am loading some more to try in my Remington 700 308 bolt action and using bettery quality brass, because I don't like shooting good brass out of the AR due to the way it beats the brass up.

I was kind of surprised to see after weighing about 10 different brands of brass that 7.62x51 was not always heavier than 308 brass.

[44 AMP]

I don't see what it is that you're looking to prove. Your brass is only about 10gr difference weight in batches and your max velocity spreads are about 50fps and most half that, or less.

Seems to me this is within the normal range of tolerances /margin of error and the differences while measurable, do not have a practical significance that I can see.

Interesting results, but to what end??

[Shadow9mm]

Originally Posted by 44 AMP

I don't see what it is that you're looking to prove. Your brass is only about 10gr difference weight in batches and your max velocity spreads are about 50fps and most half that, or less.

Seems to me this is within the normal range of tolerances /margin of error and the differences while measurable, do not have a practical significance that I can see.

Interesting results, but to what end??

My understanding is this was a test to see what if any difference was created by using the same load in different brass. It has always been recommended that when changing primers, lots of powder, bullets, or brass one should re-work the load to make sure it is safe. In this test the same everything except the brass itself to see if changing head stamps provided any significant variation.

[RC20]

I have weighed a fair amount of 308 Brass as well as 06.

The military being heavier is an Urban Legend. Probably back in the dark ages before they had digital scales !

In 06, FC is usually the heaviest with Hornady on the lighter side. RP is just down from FC and very close to Lapua. About 20 grains difference from FC down to Hornady (I think that was the lightest)

308 followed the same relationship.

Unclenick did an excellent post on how little difference there was in the real world percentage wise in the diff.

Using what I am sure some would call totally unscientific (satisfied me) I have put a case full of fine ball powder and weighed it. Overfill, use a sharp edge and scrape off.

Difference was in 3/10 4/10 if I recall. I will repeat it when I get a chance.

[lugerstew]

Thanks for the info on military brass and 308 differences not set in stone.
I am just gathering some info on my 15 or so different headstamp 308 and 7.62x51, so that when I want to load up some rounds for the AR10 and I don't have the exact one that my records show from when I worked up the loads, I can find some brass that is close in weight and knowing I am not at max and more toward mid-range loads, I can just use some of the others.
I pick up sooooo many 308 empty cases at the range, that I am sitting here with zip lock bags with only 15 to 30 or so cases in each bag, but in a lot of different headstamps.
I figure if I am diligent about always trimming and prepping them all the same, I can weigh them and if they are within 5 or 10g, I can still use them for that load.
I know the best way is to fill them with water and weigh the water, but I just can't get into that.

[scatterbrain]

Lugerstew, I load .308 brass for a friend who has both 7.62 and .308 brass. i sort and reduce the load in the 7.62 by 1/2 grain. I have shot this a lot over the chrono and find an average difference in velocity of only 10 fps. these are 10 shot groups. I sort my own ammo by head stamp and weight to within 1 grain. Does it make a difference, I have the time.

[Unclenick]

Lugerstew,

A couple of things:

The commercial headstamps you picked are heavier than some others. I have some 20-year-old Winchester that averages 156 grains. More recently, it has been in the low 160s when I've picked it up. Remington tended to run in the high 160s, last time I looked, and the Lapua I have is in the low 170s. Lake City brass runs in the 178-180 grain range for the most part, and I expect comparing Remington and Winchester to that is what engendered the assumption military brass is all heavier than commercial brass. As you found, it isn't always so.

The other thing to note is that weight difference is not always associated with capacity difference. If you take the SAAMI drawing of the 308 Win case head and calculate the volume difference as you take the thicknesses and cuts through their tolerances, it turns out two heads can weigh about 7 grains different without changing the height of the web. In other words, two cases with the same volume and made of the same brass alloy can weigh as much as 7 grains different. Then you find they don't all use the same alloy. Remington and Federal are close to 80:20 copper:zinc, while Winchester uses the more traditional 70:30 cartridge brass. So Remington will weigh a little more if it's brass volume is identical.

I took a bunch of different cases and weighed them and tried to predict volume difference from the weight one time. The predictions were only accurate to +/- 20%. The bottom line is you have to measure case volume rather than case weight to get a comparison of its effect.

[lugerstew]

Thanks Unclenick

Is there some kind of dry substance I can use to check case volume rather than water, lot of times I have my cases all prepped with new primer and don't want to fill with water.

Also, my Smith and Wesson MP10 says 308 on the barrel, do all AR10 guns say 308 or do some have 7.62x51 designation?
If there are two kinds, is a 308 AR made with different specs than a 7.62x51 AR?

[44 AMP]

Is there some kind of dry substance I can use to check case volume rather than water,

you can use any dry substance you want, but NONE of them will be as accurate or consistent as water.

The problem is every dry substance is made of particles and AIR. And the air space surrounding each kernal, flake, grain, of solid material is going to vary with the manner it is placed in the case.

You know the trick about using a long drop tube or tapping the case as you add powder?? This changes the volume the powder fills. Any solid will do this, to some degree, a liquid will not.

You could use almost any dry solid for gross general results but I don't think it will be precise and consistent enough for the differences you want to measure. (small differences in case volume)

[Unclenick]

I looked at doing this with small ball bearings at one point, but even spheres have more than one packing configuration they can get into, so a fluid will always be most precise. Bison Armory sells a pneumatic gadget that makes the measurement based on how much a metered volume of air raises the pressure in the case. However, since it is the as-fired volume of a case that determines its volume's effect on pressure for any cartridge peaking at a pressure that sticks the case to the chamber and stretches on firing (usually bottleneck cartridges that peak at over around 30,000 psi), you would spend less money shooting and then measuring with water before decapping the case.

[Don P]

From 15 + years batching concrete and being certified by the state D.O.T. of Florida and having my NRMCA certifications water will always give you absolute volume when measuring as 44 amp stated. Sand rock cement will always have voids of air mixed in, water will not.

[TX Nimrod]

…water will always give you absolute volume when measuring as 44 amp stated. Sand rock cement will always have voids of air mixed in, water will not.

Based on over 45 years of reloading - and measuring case capacity - this is not always the “case”. Water will NOT always give you the correct “absolute volume”. Filling a cartridge case correctly requires a precise technique, not just randomly pouring water into the neck…..that can introduce tiny air bubbles which can - and will - introduce error. The preferred method to fill the case is using a syringe with needle and filling the case from the bottom. Too, what is the “top of the neck”? I prefer to use a fired case, fill with a syringe, then lower a bullet into the neck to a mark on the bullet, this will displace out the exact same amount of water in each case and give a more precise measure of the exact amount of water needed to fill the case. I won’t even start with the purity or temperature of the water. After all, we want a real value rather an estimate.





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[RC20]

Is there some kind of dry substance I can use to check case volume rather than water, lot of times I have my cases all prepped with new primer and don't want to fill with water.

I use ball powder.

Is it Uber accurate? No. Is it relatively and realistically accurate going from case to case, I think so.

I suspect the COAL being trimmed to the same is more important.

Can two different mfg act differently when shot? Hunting probably not, target shooting, I sort and reload to mfg head stamps.

RP is a favorite, I think its as good as Lapua. Might need to be annealed more often.