.308 vs. 7.62 pressure issues and reloading


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AK103K
December 29, 2002, 10:16 AM
I know this has been discussed before as to should you or shouldnt you, especially in the FR8 rifles. I dont think it was ever addressed as to reloading the round regardless as to whos right or wrong about the differences in the rounds. What causes the difference in pressures, the loading or the chamber dimensions? Can a 308 be loaded to 7.62 specs using a lighter load, or is it a dimension thing that causes the higher pressures? I have a FR8 and primarily shoot nato spec ammo in it, but on occasion, do shoot 308 in it. I've had no trouble and dont think its really an issue, I was just curious as to reloading and the pressure issue. Any thoughts?

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riverdog
December 29, 2002, 10:30 AM
I think what you are referring to is that Lake City 7.62 NATO brass is thicker and that if you reload it to .308 specs, you may exceed SAAMI pressure limits. I shoot both. Radway Green for plinking, Fed Match for serious work. Radway Green has proven to be a fairly accurate load.

Art Eatman
December 29, 2002, 03:11 PM
Easy enough to check case capacity for comparison. Fill up a civilian case and then pour it into some military brass and see if there's powder left over. :) Or vice-versa, and see if there's space remaining in the civilian case. Thicker cases mean max pressures at approximately three grains weight less powder than book max for civilian brass.

Loading for a semi-auto, the small-base dies and full-length resizing facilitate cycling. For bolt-action, all I've ever done is resize the case necks.

By and large, op-rod rifles max out around 47,000 psi or so. The others probably are happy to the standard max of no more than 53,000 to 55,000 psi.

Bolt guns are basically maxxed at the 53/55 figure.

Roughly. :)

Art

45Badger
December 29, 2002, 06:13 PM
I've got same/similar questions.

I've been told to start loads 10% lighter when using the Lake City Brass to avoid overpressure.

Is this a good rule of thumb? Do any manuals address this specifically? Thanks!

beemerb
December 29, 2002, 10:42 PM
10% less for any military brass.
Bob

boing
December 30, 2002, 12:37 AM
OK, now is that 10% less than the commercial max, or 10% less than the 10% less than commercial max...if you get my meaning.

You start developing any new "civilian" load at 10% below published max, right? Do you then go 10% below that when using military brass?

AK103K
December 30, 2002, 07:31 AM
I guess I didnt get what I was trying to ask across. The threads I've seen discussing this dealt with commercial 308 having higher pressures than the 7.62 NATO, or so the argument went. The issue was, the 308 was unsafe in the FR8 guns, due to the pressure differences. Something about steel or receivers, or even the wrong gun(FR7), I'm not sure which. What I dont understand is, where does the difference in pressure come in? The rounds are only slightly different in dimensions, to the point of interchangeability. This pressure difference is prior to reloading, so thats not really the initial issue, but is it related? I have a copy of the Lake City load manual from the late 60's. I dont see much difference in loads, from commercial 308, so I'm thinking the answer lies somewhere else, chamber spec, possibly? I understand the issue of downloading military brass 1 grain due to case thickness, and all the other problems with it, but I dont think this is whats causing the pressure problem initially. What I'm asking, or think I am, is, if there is a pressure problem due to differences in the rounds, can that be addressed with reloading, so the rifle can be fired safely using reloaded 308 brass and loadings in rifles, like the FR8, that might have an issue with it?

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