Home Forums Reloading Big Game Rifles Temp Stability (MIL-SPEC)

I've been interested in temp stability for the powder, bullet, cartridge combos I have. Upon asking manufacturers about a particular powder stability I've occasionally received the answer, "it meets the military spec." But then they wouldn't tell me what the spec is. I happened to run across the spec for the M80 (7.62x51) and M855 (5.56) today. The short of it is ammo is tested at 70deg(or 69) and then at -65 and 125 for the 7.62 and -20 and 122 for the 5.56. The ammo can't lose more than 250FPS. Useful just in case you're in a bar bet someday...

Got a link to your source?

Thanks.

5.56

3.10 Temperature stability. The action time, pressure and
velocity of sample cartridges conditioned and fired at the
temperature extremes specified below shall be in accordance with
3.10.1, 3.10.2, 3.10.3, and 3.10.4.
a. Conditioned at 125 ~ 20F for not less than one hour
and fired at that temperature.
b. Conditioned at –65 + 20F for not less than one hour
and fired at that temperature. —

3.10.1 Velocity. The average velocity shall not decrease by
more than 250 f~s from the average velocity of the sample
cartridges conditioned at 70° —+ 2° F. Any increase in Velocity is
acceptable.

3.10.2 Chamber pressure. The average chamber pressure
shall not vary from the average chamber pressure of the sample
test cartridges conditioned at 70 ~ 2° F by more than 7000 psi.
The average chamber pressures of the sample cartridges of the same
lot conditioned at 125° ~ 2° F shall not exceed 60,000 psi. Any
decrease in chamber pressure is acceptable.


7.62


3.7.1.5 Velocity. The average velocity of the sample
cartridge conditioned at 70° F, shall be 2,750 feet per second
(ft/see) plus or minus 30 ft/sec at 78 feet from the muzzle of the
weapon. The standard deviation of the velocities shall not
exceed 32 ft/sec.

3.7.1.6 Velocity. The average velocity of the sample
cartridges subjected to 125° F and -65F storage conditions shall
not vary from the average velocity of the sample cartridges of the
same lot conditioned at 70° F by more than plus (+)150 or minus
(-)250 ft/sec.



"...at 78' from the muzzle..." Interesting chrono location.

WC844 (H335), and WC846 (BL(c)2) are some of the worst powders made in terms ot temperature stability.

Not much of a standard to aspire to.

I don't see that standard as useful at all in picking a hunting powder. Don't care about -65 and 250fps is pretty excessive in my opinion. But now I know why I got that answer. It was another way of saying it's crap.

Thanks for that. It really doesn't seem like much of a high bar, does it?

In fairness, there is apparently a different standard for M118 Long Range ammo. The MIL standard for that is limited distribution so I can't get a copy and what, if any, extreme temperature standards they have applied.

It's MIL-DTL-32288 if anyone has access

The Navy wasn't happy with M118LR so they developed Mk316 mod 0. Don't have spec, but they placed emphasis on accuracy and consistency from -25 to +165deg. They went with a modified extruded propellant.

Interestingly, at the same time, the Navy developed the 300 WM as a sniper rifle. That ammo spec is available and it states the following:

"The average corrected muzzle velocity of the sample cartridges conditioned at -20°F shall not vary by more than 75 fps from the average corrected muzzle velocity of the sample cartridges conditioned at 165°F." http://usarmorment.com/pdf/300WM_load%20data.pdf

That's pretty solid performance. As an aside, they use 10, 10-shot groups for their accuracy standard. That'd get expensive if I tried that!

I believe the latest version of the M855 ammo is loaded with what's sold as CFE-223. It's made by St. Marks powder in florida and is a ball powder, easy flowing through loading equipment but not really temp resistant by today's standards.

Mil-spec is a term that doesn't mean much to a guy looking for precision in his handloads. There are a lot of criteria that makes something "mil-spec" and most of them have to do with reliability, whether or not it shoots particularly well is pretty far down the list.