In article , Bob Crantz
wrote:

"Peter Wiley" wrote in message
. ..

Shrug. My memory is out about the chambers & pressures, but I'm right
about the case sizes. I've reloaded *heaps* of boxer primed ex military
brass, used to buy it for peanuts at gun shows, fired it
interchangeably with commercial brass in both a Rem 700 Varmint and a
Ruger Mini-14. However, it's quite safe to fire 223 Rem ammo in a
military 5.56 NATO chamber. Ruger Mini-14's have been chambered for
both and I used to use one regularly with ex mil 5.56 NATO ammo without
any noticeable ill effects. Maybe because the Rem 700 was a high
quality rifle not a cheap POS.

http://www.thegunzone.com/556v223.html has some interesting comments.

The most likely effect of an over pressure round is a backed out primer
and a possibly binding action, not a rifle going 'kaboom and messing up
your face'. Not desirable, but not the end of the world either. Ask any
serious handloader who's worked up 'hot' loads a bit at a time.

Still, you learn something new every day, hey? No need to thank me for
expanding your knowledge base. If I get bored I'll dig out my reloading
manuals and compare bullet weights & velocities. I assume you do
understand the TANSTAAFL concept insofar as it's pretty hard to get
higher MV with the same bullet weight and less chamber pressure. Of
course that depends somewhat on the powder you've used, but frankly,
I'm not that interested these days and if all you want to do is
endanger your neighbours, you don't need to reload your own ammo.

PDW

The military cases are thicker than commercial and the primer is swaged.

Yep. I used to use a primer pocket reamer to remove the crimp after
punching out the primer.

The
military case holds a little less powder so the CUP (copper units of
pressure) is higher with a commercial load in a mil case. I've separated
cases with occurs just above the base. It can be a crack to complete
separation. I've done it in military semi autos and bolt action rifles.

Never had this happen with 5.56, have seen it happen with .243 reloads.
I put it down to having my full length sizing die set too fine and
moving the case shoulder back a bit.

A
modern firearm is designed to blow the separation away from the face. The
gun does not blow up. You'll notice the headstamp flattened out and the
primer pocket flattened. With rifle rounds, you can't double charge the load
as in pistols so the chances of ever loading something that can burst a
receiver is almost non existent.

IIRC I was using a compressed load of WW 748 - *no* chance of a double
load at all.

OTOH using Unique in 44 Mag cases it was certainly possible. Never
happened to me tho.

PDW