From: magnum@cs.umd.edu
Newsgroups: rec.guns
Subject: followup on hangfires
Date: 19 Aug 92 23:43:40 GMT


A poster tonight got me thinking of hangfires vs. running dry.  Today I was at 
a favorite armory, out to snarf up the primo works of art they'd taken to Perry
to shag orders.  Found one, and got, as usual, a nice runthrough of safety
procedures on the service rifle.  This one had a few embellishments I'd not
heard before, one concerning hangfires.  The 'smith reminds us that if the
hammer drops on a round (in, say, M1A or M1 Garand) that this military firing
pin is constantly pushed up into the primer, no spring return.  If the round
does not ignite, then additional impacts to the rifle can impart energy to 
the pin into the primer, which might be enough to make the round ignite after
all.  So ... don't go jiggling the operating rod, especially to partially pull
it back to check if there really is a round in there!   Points out that this 
is an easy way to lay your arm wide open, if not invite an out of battery 
detonation.   The latter especially would be Bad (tm).   What he advocates as
an alternative is to pry open the trigger guard, just like you're disassembling
the rifle, which you know cocks the hammer.  Then you can get the safety on, 
and the hammer is away from the primer.  It should be needless to say, though
I say it anyway, that the whole time you are pointed in a safe direction.  He
did not advocate using this technique to cock the hammer for another snap (a
cute way to do it without opening the breech up) since of course you really
don't know why the firearm or ammo malfunctioned, so why increase the risk?

Other trivia:  Don't chamber a round in an M1A without the magazine inserted.
Always insert the round into the fixed magazine, and let the bolt chamber the
round instead.  The rifle is *built* to have the extra resistence from the
mag etc slow the bolt down, chambering things properly; without this resistence
there is sufficient energy driving into a round that it could detonate without
the minor detail of your having pulled the trigger and dropped the hammer.
I have seen lots of shooters do this in slow fire.  Probably have done it 
myself.

Other trivia:  During the lecture about *why not* to use handloads, besides to
reduce his liability.... Many shooters (including me!) are measuring headspace
by firing a new, soft-brass round and then measuring it with an RCBS mic.  Well
he says this fails for a gas gun.   Okay with bolt gun, he says, but in most
service rifles there is still some pressure (reduced to be sure) on the inside
of the case, that can let it expand to slightly larger than the real headspace
as it is ejected. Even if not, then there is plenty of torsing and contorting
and who knows what going on, so the measurement is skewed.  His claim was that
know-it-alls consistently claimed this was bullsh*t, and he consistently has
shown them wrong by checking headspace with inserts, rather than by formed
brass, and showing people on their own rifles that they were too large by a
couple thousanths.  Why is this a big deal?  Since people who are concerned with
headspace like this are handloaders, and most handloaders will, assuming they
full length size as they should, try to get the headspace within a few thousanth
for accuracy.  But ... get a little dirt in the chamber, fouling or whatever,
you imped the cartridge going into the chamber enough to invite, with said 
military firing pin described above, an out of battery detonation.  So ....
the bottom line is he begged me not to use handloads, and, if I did, at least
to avoid trying my own measurements, in favor of sizing to SAAMI specs or less.

Cheers,

Magnum