.308 case pressure?

rchawk

Hi gang,
Here is a question I should probably know the answer to, but I don't.
Most reloading manuals tell you to reduce loads by 10% when using military cases due to reduced volume. Now, Accurate Arms lists a 168 FMJBT load of 2230C as "37.8 up to 42.0 grains". Does this mean I should reduce the powder by 3.78 up to 4.20 grains respectivly???
Also, will a much reduced load still function a NM M1A?
As always, thanks in advance.

Hawk


I would rather be tried by 12 than carried by 6!

Mobuck

More or less, yes. The recomendation to reduce the charge in military cases applies to the range of loads. It is assumed that you will detect signs of increasing pressure at the top end and stop at a safe level. Therefore, the caution should apply to starting loads but kept in mind as you increase charges and stop at or before 10% less than the quoted max charge.

Mobuck

rchawk

Thanks Mobuck,
Interestingly enough, I was more concerned with failure to function in my M1A at the lower end of the loading scale. I know what to look for at the overpressure end.
Won't the "auto" pressure regulation on the M1A compensate for the reduced loads to a certain extent?
Thanks again,

Hawk


I would rather be tried by 12 than carried by 6!

redcedars

Hi rchawk:

I think you may be confusing the .308 Winchester with the 7.62x51 NATO. While they are very similar, they are not identical. Green Lantern posted a link to a site which describes the differences in detail, and there have been several threads posted her on the subject, so do a little research. The nominal chamber dimensions for the 7.62x51NATO are a little different, and for maximum accuracy you should determine the exact dimensions of the chamber of the particular gun. One of the guys recently discovered his match tight .308 Win chamber wouldn't accept 7.62x51NATO cartridges properly as it was a couple of thousandths too small.

Having said that, the 7.62x51 NATO case does have a smaller case volume which will generate higher pressures than a .308 Win case, all other things being equal.

redcedars

GreenLantern

Here is one link I have, probably the one redcedars mentioned. Somebody had posted it on this forum before and I just saved the like. I think I maybe have another bookmarked at home that I'll look for later tonight.


http://www.smellysmleshooters.net/ammopressure.htm

GreenLantern

http://www.fulton-armory.com/308.htm

Here's from fulton armory, but don't forget they are in the business of refurbishing the M1A.

GPWEAPON

Just pick a load in the middle of the listed specs and shoot it. one thing you will notice is an increase in pressure with the bullet deeper in the case. in the M1A you can only hang them out so far if your shooting rapid fire, but if your shooting single rounds like for longer shots at varmints you can get them out to the lands and will drop the pressure. Watch out for 2520 its heat sensitive, I once blew the bolt of an M1A out the primer hole sheared off a piece of the bolt blew out the magazine and put a bruize the size of a basketball on my forearm, I was in prone, 180's to the max on a hot day on 1000 yd range, never again,