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From: sfaber@ihlpb.att.com (Steven R Faber)
Subject: Re: Pressure Signs, Favorite Loads
Organization: AT&T

#From article <54636@mimsy.umd.edu>, by bbx!bbx.basis.com!russ@unmvax.cs.unm.edu (Russ Kepler):
#
# In article <54538@mimsy.umd.edu> ole@brutus.delab.sintef.no (Ole-Hjalmar Kristensen) writes:
# #If you mean that the primer popped partially out of the case, this is
# #usually a sign of lowe than normal pressure.
#
# Huh?  (I always like to start one of these posts on the right foot
# with a sure sign of intelligence...)
#
# I've never heard of this, and would expect that a primer backing out
# would be a sign of high pressure and good containment be the case and
# bullet, leaving only the primer to either blow or back out of the case.
#
# I had some new loadings in .308 (new cases, neck sizing only, 5%
# reduction from Ken Waters' maximum in 4895, 168 grain MatchKing - a
# real standard load) back out the primers recently.  Some of the
# primers came out far enough to bump the extractor off the case (or the
# case shoulder hadn't set) so far that I needed to raise the rifle
# "barrel up" for the case to come out.  I'm finally chalking these up
# to new cases and starting out with a full length resizing.  Those
# cases that were fully sized had no problems with the same loading
# (powder, bullet, seating depth and non-crimp).


I have seen backed out primers from cases that were sized too short
and in old rifles with excessive head space, in other words when
the bullet is too short for the chamber.  Don't know about the
low pressure case though.


From: ole@brutus.delab.sintef.no (Ole-Hjalmar Kristensen)
Subject: Re: Pressure Signs, Favorite Loads
Date: 8 May 92 03:21:14 GMT
Organization: SINTEF DELAB, Trondheim, Norway.

In article <54636@mimsy.umd.edu> bbx!bbx.basis.com!russ@unmvax.cs.unm.edu
(Russ Kepler) writes:

   In article <54538@mimsy.umd.edu> ole@brutus.delab.sintef.no
   (Ole-Hjalmar Kristensen) writes:

   #If you mean that the primer popped partially out of the case, this is
   #usually a sign of lowe than normal pressure.

   Huh?  (I always like to start one of these posts on the right foot
   with a sure sign of intelligence...)

   I've never heard of this, and would expect that a primer backing out
   would be a sign of high pressure and good containment be the case and
   bullet, leaving only the primer to either blow or back out of the case.

   I had some new loadings in .308 (new cases, neck sizing only, 5%
   reduction from Ken Waters' maximum in 4895, 168 grain MatchKing - a
   real standard load) back out the primers recently.  Some of the
   primers came out far enough to bump the extractor off the case (or the
   case shoulder hadn't set) so far that I needed to raise the rifle
   "barrel up" for the case to come out.  I'm finally chalking these up
   to new cases and starting out with a full length resizing.  Those
   cases that were fully sized had no problems with the same loading
   (powder, bullet, seating depth and non-crimp).

   If you know where this has been discussed I've love to read about it.

   --
   Russ Kepler, Basis International Ltd. russ@bbx.basis.com  phone: 505-345-5232

Yes, that is easy, but I'm not sure it will help you very much. It's
discussed briefly in "V}penjournalens Ladebok" , which is a Norwegian
reloading manual. However, it doesn't say much about the subject, just
that it is more likely low pressure than high pressure.

I have experienced the phenomenon myself, in a single-shot .357 mag.
rifle with a very tight chamber while developing some new loads. I
don't have the exact data available, but what happened is essentially
this:

Heavy load: severely flattened primers and some cratering.
Normal load: slightly flattened primers.
Somewhat less than normal: primers popped out, no flattening at all.
Reduced load: no flattening, no popping.

The case diameter as measured with a micrometer indicated that the
pressure was decreasing as I reduced the powder charge, so I don't
believe there was any detonation going on. Besides, the powder I used
(N340) has a medium burn rate, much like Unique. (I was looking for a
load with little muzzle flash, not maximum velocity)

I think maybe that what happened was that in the tight chamber, the
pressure was enough to make the cases cling to the wall of the
chamber enough to let the primers back out.

I would also very much like to know if anyone has a definitive explanation.


From: ole@delab.sintef.no (Ole-Hjalmar Kristensen)
Subject: Re: Primer Backing Out
Organization: SINTEF DELAB, Trondheim, Norway.

I suppose what happens is that the case clings to the chamber wall,
allowing the primer to be pushed out. The pressure is probably not
high enough to push the case back towards the bolt face with any
force. I have had this happen to me with loads that are on the low
side, and the phenomenon disappears if you increase the pressure. (or
grease the chamber :-)


--
Ole-Hj. Kristensen

"If you are going to shoot, shoot, don't talk."
		    -- Il Bruto


From: ohk@nta.no (Ole-Hjalmar Kristensen TF.DT/DELAB)
Subject: Re: Primers backing out!?
Organization: Norwegian Telecom Research

In article <D0BrBo.Fu6@ns1.nodak.edu>, grjohnso@plains.NoDak.edu (Gregory
A Johnson) writes:

|> Arvola William (arvola@sol.acs.unt.edu) wrote:
|>
|> : I've noticed that the primers appear
|> : to be backing out somewhat on .357mag
|> : cartridges fired from my Rossi .357
|> : lever-action rifle [Winchester-92 clone].
|>
|> : Should I be concerned?
|>
|> Yes you should be.  You most likely have an overpressure condition which
|> can be caused by several things.  The possible headspace problem you
|> mention could cause this if the bullet is contacting the lands or is
|> forced into the lands when chambered.  Have you been checking your
|> maximum case lengths and maximum cartridge lengths?


Well, this *may* be the cause, but overpressure is not the only reason
for primers backing out. I have experienced the same with a .357 single
shot rifle, and did the following observations: (pressure levels
determined by measuring case expansion). All loads at least 2 mm short
of connectting with the lands.

Loads at .38 Special pressure levels: primers not backing out.
Fairly tame .357 loads: Primers backing out, but not flattened.
Standard .357 pressure: No backing out, slightly flattened primers.
*VERY* hot .357 load (Near .357 Maxiimum): Blown primer or excessively
flattened.

Others have made the same observations. So what is happening here? The
rifle in question has a rather generous recess which accommodates the
rim of the cartridge, which means that there is some play. When the gun
is fired, the cartridge is first slammed forward by the firing pin,
then the primer goes off.  With the right pressure, the case expands
just enough to cling to the chamber walls, which means that because of
the free space behing the case, the primer has room to pop out.
Look at the primers. If they are flattened or cratered, you may well
have overpressure. If not, the above explanation is the most plausible.
The primers stop backing out if I seat the bullets far enough out that
they touch the lands, which effectively removes the excessive space.

If you are reloading, you can check your pressure against factory
ammunition by measuring the maximum diameter of the pressure ring on
the case with a micrometer. Measure at least 5 cases of both factory
and reloaded ammo, (which must both be shot in the same gun, of course)
and use the average.

|> If the headspace is not the problem, try backing off on the powder some.
|> Would you be using magnum primers by chance?  Magnum primers require
|> quite a significant cut in amount of powder to maintain safe pressure levels.
|>
|> : A book I have suggests that I have
|> : headspacing problems.  Is it possible
|> : to have headspacing problems with a
|> : straight-walled rimmed revolver
|> : cartridge?


Yes, I would say that my rifle has excessive headspace. However, it is not so
excessive that it is a significant problem.


From: bartb@hpfcla.fc.hp.com (Bart Bobbitt)
Newsgroups: rec.guns
Subject: Re: Garand question
Date: 14 Apr 1994 13:38:52 -0400

Don Baldwin (donb@netcom.com) wrote:

: On some of the
: cases, the primers looked like they had backed out the teeniest bit.  And
: the bottoms of the cases looked very slightly bulged, about 1/4 inch back
: from the head.

This is a very normal occurance when peak pressure is far below the
normal, maximum amount.  What happens is the case is pushed forward by
the firing pin as the primer is struck.  When the case expands to fill
the chamber, the lower-than-normal pressure isn't enough to push the
back of the case fully against the bolt face.  But the primer isn't 
held in place with much tension, so it gets pushed back against the
bolt face.  Max pressure cartridges push the case head hard against 
the bolt face; there's no place for the primer to stick out its pocket
against. 

If the new brass has smaller than normal diameters just in front of the
extractor groove, it will bulge out to a much greater diameter than the
case has; another normal thing even with maximum loads.

FMJ bullets have about the same jacket hardness as hunting bullets, so
I doubt if this is the cause.  If you barrel's groove diameter is on
the large size, some factory ammo won't generate normal operating pressure
and that may be the cause of the primer's backing out.

BB


From: bartb@hpfcla.fc.hp.com (Bart Bobbitt)
Subject: Re: Mauser questions
Organization: Hewlett-Packard Fort Collins Site

Marc Cassidy (marcc@ecs.comm.mot.com) wrote:

: One thing I've noticed is that the thing is starting to
: push the primers out of the pocket just a tiny bit (slightly
: more than flush with the cartridge base). I realize that
: this is the beginning of head space problems. My big
: question, is it time to stop shooting the gun?

I doubt if the rifle's headspace is the problem.  It may be one of these.

If you are shooting reloaded ammunition, the powder charge may not be
enough, either by design or by accident.  When the firing
pin forces the cartridge fully forward in the chamber as it detonates
the primer, the case expands.  But it doesn't expand enough because of
lower than normal pressures.  The case side walls grab the chamber walls
but the head of the case doesn't go all the way back against the bolt
face.

The other problem may be that you are setting the shoulder back too much
if you're full length resizing the cases.  This lets the case go too far
in the chamber and can cause the same situation as noted above.

The last possibility is the barrel is very worn out.  Not enough pressure
is generated and causes the above situation to happen; even with normal
new factory ammo.

A competant gunsmith should inspect the rifle and your ammo.  It's easy
to determine what is causing the problem once the rifle and ammo is
correctly evaluated.

BB

From: bartb@hpfcla.fc.hp.com (Bart Bobbitt)
Subject: Re: Load pressure question...
Organization: Hewlett-Packard Fort Collins Site

Minh Lang (minh@inst-sun1.Jpl.Nasa.Gov) wrote:

: I would appreciate any comments to the following:

: - Definitely there was high pressure as the primers were backed out?

I don't think you had enough pressure; it was too low.  With high
pressure, the case head would have been forced against the breech
face and the primer would only have gone back just as far.  The primer
would be flush with the case head.

: - What caused the bulge in 180 degree near the case head? Not the
: headspace, I believe, since the brass I used were once-fired from
: new by myself in the same gun&barrel and they were neck sized
: after the first firing.

One side of the case was thinner than the other.  That's probablly the
side that bulged out.  This is a very normal thing.

: - This high pressure symptom developed at 2.5g under the suggested
: maximum load was due to my *long* OAL? (only 0.005" off-the-land)

Again, you had too low a pressure, not too high.

: - Should I trash all these brass even thought I found no thinning of
: any kind? Or can I full-length resize them and reload again, since they
: are only twice-fired now? If I can, should I FL resize and not pushing
: the shoulder back? (I have FL resized one of these cases by
: not touching the shoulder - back off the die half-turn
: from where it touches the shell holder -  and the round was chambered
: easily)

Full-length size those cases, but don't set the shoulder back more than
one or two thousandths of an inch from where they headspace as fired.
Your brass will last much longer and typically be more accurate this way.

BB

From: bartb@fc.hp.com (Bart Bobbitt)
Subject: Re: Cratered Primers
Organization: Hewlett-Packard Fort Collins Site

Bill Meyers (meyers@leonardo.rtp.dg.com) wrote:

: I've been working up loads for a new .308, and noticed something
: interesting.  I'm using new cases, and the case heads are slightly
: conical -- not much, but enough to see by laying a straightedge
: across the head of each case and looking "through" it at a light
: source.  These (new) cases go through the following states with
: increasing pressure:

: 1)	Head conical, fired primer sticks out a few thou.

New cases typically have their primer pocket edges a couple of thousandths
of an inch below a plane across the edge of the rim.  This happens as
the primer pocket is stamp-swaged in and the flash hole is punched
through the bottom of the primer pocket.  Such a technique can't help
but put the inner part of the case head further forward than the rim's
edge.

It's very typical with new cases charged with a few grains less than a
maximum powder charge for that barrel, chamber and handload components
to have the primer protrude several thousands from the case head.  Those
cases can easily be five to ten thousandths of an inch shorter in
headspace than the headspace of the chamber they're first fired in.
The case doesn't expand enough to completely fill the chamber.  It's
driven forward against the chamber shoulder, then as the pressure peaks
the case walls press against the chamber walls and the back of the case
doesn't completely flatten against the bolt face.

: 2)	Head unchanged, fired primer sticks out a bit less.

The resized case headspace is now closer to what chamber headspace is.
But the powder charge still is too light to completely expand the case
to fit the chamber.  Peak pressure still doesn't press the case head
against the bolt face completely; if it did, the primer would be flush
with the case head.

: 3)	Head flatter, fired primer sticks just a tiny bit.

After the second resizing, the resized case headspace is getting closer
to chamber headspace.  There's less distance now for the case head to
move back as its walls grab the sides of the chamber.  Only a couple
of thousandths primer protrusion from the case head exists.

: 4)	Head flat, fired primer doesn't stick out at all.

Finally, the resized case headspace is only a couple of thousandths of
an inch shorter than chamber headspace.  As the case head now goes
fully against the bolt face, the primer can't back out of the case and
it will be flush with the case head.

: Clearly I'm "seeing" these new cases fireform to fill the chamber.
: My question for the net:  have I reached max pressure when the case
: head first gets entirely flat?  I.e., as soon as I reach state 4) ?
: (Hope it isn't _before_ that ...  :-)    Thanks!

Assuming you use the same primer, powder-type/charge-weight, bullet and
seating depth, case make/lot and reloading processes, the peak pressure
is the same regardless of how many times the case has been fired.  If
you increase the powder charge weight to an amount closer to what's
maximum in your rifle for the components you use, you won't see this
primer protrusion dimension start large, then decrease as a new case
is first used and resized/reloaded a few times.

BB


 






































































































































































































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