Military brass and pressure

[Danth]

I've been using military brass to form many different cases. I understand there is less volume in a military case, thus increased pressure. It's been recommended reducing charges by a grain or two when using military brass. My question is, with the increased pressure, is there an increase in velocity?

[Winger Ed.]

My question is, with the increased pressure, is there an increase in velocity?

Yes,
With a given powder, more & more of it in the same volume of case:
You'll get an increase in pressure, and you will also have an increase in velocity.
The slightly decreased volume of GI brass just gets you there a little sooner.

[Hick]

Not all types of military brass have smaller volume. A few years ago I did comparisons on several brands of commercial and military 5.56/223 brass and discovered that some types of military brass were identical to some brands of commercial. If you are not sure about whether the type of military brass you have has less volume, just size and weigh the case, compared to a sized and weighed commercial case. Since the outside dimensions are the same, and the brass density doesn't vary much, any added weight is on the inside.

[TurnipEaterDown]

If you have question on the weight of brass, weigh it.
Reduction in internal volume (by changing casing weight) does make a difference, and the practical aspect is: how much weight change makes a difference in terms of velocity/pressure for practical matters.

This 'military brass is heavier/thicker' advice has been around a long time, and was almost certainly meant with good intentions. Maybe it is often true, but there is the problem, 'often'.

I have used some pretty varying lots of 30-06 brass over the years, both military & commercial from 1950s, 60s, 70s, 80s & 90s. Some early stuff I had was inherited / scrounged. What I Generally saw after questioning this weight statement was that Older commercial brass was Often Lighter. Seems that newer and newer commercial brass got heavier. My memory is that there was Quite a difference between 1950s Winchester Super Speed and 1990s Win & Rem commercial brass. More so than military.

Sidebar note w/ some speculation:
I also found that commercial brass gave better accuracy -- likely due to concentricity being better on commercial.
The older military accuracy spec for infantry rifles going into WWII wasn't too spectacular by today's sporting rifle standard, and so the ammunition spec that mated to it probably wasn't so stellar either. Since the 06 & attendant competitors went out of front line service in most countries soon after WWII, I doubt the manufacturing specs had much reason to change.

There is a nice section in the Norma reloading guide #1 that gives info as to effect w/ internal volume changes.
They made 300 Win Mag brass w/ differing specifications, and have changed their reloading data to go with the lot. It can make a difference.

[Castaway]

The warning is real. Once I was using Lake City, 30-06 brass and didn’t heed the decrease by 5% guidance and loaded “by the book.” As a consequence, I blew the extractor off of a Savage bolt. A couple of notes: as the pressure cure goes up, so does the velocity proportionately, to a point. At some point, the velocity curve will flatten out as the pressure increases. When it gets there, you’re already past the point at which you should have stopped. There’s no need to size if you’re going to weigh for a comparison, it’s the same amount of brass wither way.

[truckjohn]

It's easy enough to measure case water volume. Just fill one up and weigh it. I prefer fired cases, as it gives an idea of the chamber volume.

I agree that "thinner sporting brass" isn't always the case.

[Danth]

"If" the internal volume of military brass is less, producing higher pressure and velocity isn't the reduced volume more efficient with reduced powder charges? Wouldn't reducing the volume and powder charge until velocity was effected negatively result in the most efficient cartridge?

[sundog]

I do not know where the idea, "military brass has less volume", came from. It is not always the case (pun intended).

Do a search for 'cartridge brass weights comparison', and you might find some interesting material.

Weigh some of your unprimed and clean cases.

[pworley1]

When I start to work up a load using G.I. brass, I take a piece of the brass I will be using and fill it completely with the powder I will be using then weigh it. Then I transfer the powder to a piece of commercial brass. If it fills the case I use standard load data to start. If it is not full, I fill it completely and weigh it. I reduce my starting loads by the difference in the weights.

[Char-Gar]

Every piece of USGI 30-06 and 7.62 brass I have inspected, loaded and fired have been thicker and heavier than any commercial brass I have inspected, loaded, and fired. I understand this was to withstand the jerk of automatic weapons.

I also have thousands of military 38 Special cases. The LC (Lake City) and WCC (Winchester Cartridge Company are heavier and thicker and the RA (Remington Arms) and FC (Federal Cartridge) are not.

Not all USGI 30-06 and 7.62 are uniform in weight, thereby internal capacity. They vary considerably with contractor and lot. Commercial brass is more uniform as is military match brass.

I know zero about the little mouse gun 22 military brass. I have never owned, fired or reloaded for one of those dinky little things. Going to war with a plastic and alloy rifle chambered for a centerfire 22 round, Lord have mercy!

[Larry Gibson]

I've been using military brass to form many different cases. I understand there is less volume in a military case, thus increased pressure. It's been recommended reducing charges by a grain or two when using military brass. My question is, with the increased pressure, is there an increase in velocity?

With a given load the thicker the brass the less capacity. Ergo with that given load there will be an increase in pressure and an increase in velocity.

[nicholst55]

FWIW, USGI 5.56X45mm NATO brass generally weighs just about the same - or less - than commercial brass for .223 Rem. The case necks are normally a tad longer than commercial .223 brass, so I always trim them before the first use. This is due to the chamber specs being slightly different between the two chamberings. The NATO chamber has a longer throat than most .223 Rem chambers.