Signs of Over Pressure?

Redhook · May 6, 2002, 02:52 AM

Can you guys give/show me some examples of what to look for in spent brass that has been over pressurized? I know many of you use the flattened primer as an example, but even factory ammo comes out of my .308win Rem 700 with primers that are slightly flattened and are textured, I assume, in the face of the bolt.

I guess what I am looking for is more detail as to what happens to a spent case when it's over pressurized.

Thanks
-Red-

Frohickey · May 6, 2002, 04:38 PM

Check out the Speer reloading manual. There are gobs of pictures there about cratering primers, bulging cases heads, flattened primers, etc.

Khornet · May 8, 2002, 06:43 AM

When pressure is getting too high, two main primer signs are:

"Cratering", which means that the indent from the firing pin develops a raised rim when primer metal flows into the gap between the firing pin tip and the rim of the firing pin hole in the bolt face.

"Flattening", when the primer metal flows to fill the pocket completely so that there is no detectable groove between the primer and the rim of the pocket. Usually after firing there is still a little bit of radius left on the bottom of the primer's cup sothat if you drew a needle across the primer from its center toward the rim of the primer pocket it would fall into that little groove where primer metal meets case brass.

Some say another sign is the appearance of the outline of the extractor cut raised in relief on the case head.

Poodleshooter · May 8, 2002, 11:26 AM

Another quick way to check a case is to run your fingers down the sides of case, feeling for a slight dip down around the casehead, or just ahead of any belt. That may indicate a stretching casehead, when the presence of a shiny case or no primer may lead you to think that the case is relatively new.

KP95DAO · May 9, 2002, 10:42 AM

By "over pressurized" I take it you mean that the brass has been stressed beyond it's limits. There is only one reliable check for that. That is checking case head expansion at the solid portion surrounding the primer pocket. To do this you have to know the measurment before the firing. However a simple way is if the primers seat more easily than normal you have expanded the primer pocket and solid head. This is not where you want to operate repeatedly with a piece of brass. And by operating there you have removed all your safety margins. If some variable goes beyond the norm under these conditions you will have serious problems!!!!!

A reliable test for excessive pressure with most all guns is "sticky extraction." Though this can be caused by a dirty chamber or a chamber with rough walls it is time to start looking for the cause if you run into this indication.

Chemistry · May 9, 2002, 02:26 PM

Primer flattening may not necessarily be a true indicator of pressure.

For example, when I load up some .45 ACP cartridges, using 230 grain FMJ, in combination with a 6.0 grain charge of Hodgdon Universal Clays, I get flattened primers if I use Federal primers (soft).

If I use CCI primers (hard), there is no flattening.

Steve Smith · May 9, 2002, 02:31 PM

Flat primers can also me an indicator of a too-light load. Are you confused yet?

**Mal H** · May 9, 2002, 05:30 PM

The way a primer looks might be a good indicator of a high pressure excursion, but the only consistent indicator is the case head expansion KP95DAO mentioned. Either that or you could purchase about $70,000 worth of test equipment.

C.R.Sam · May 9, 2002, 06:30 PM

Mal speak true.

Sam

May 6, 2002, 02:52 AM	#1
Redhook Senior Member Join Date: January 25, 2001 Posts: 254	Signs of Over Pressure? Can you guys give/show me some examples of what to look for in spent brass that has been over pressurized? I know many of you use the flattened primer as an example, but even factory ammo comes out of my .308win Rem 700 with primers that are slightly flattened and are textured, I assume, in the face of the bolt. I guess what I am looking for is more detail as to what happens to a spent case when it's over pressurized. Thanks -Red-

May 6, 2002, 04:38 PM	#2
Frohickey Senior Member Join Date: February 4, 2002 Location: People's Republic of Kalifornia Posts: 579	Check out the Speer reloading manual. There are gobs of pictures there about cratering primers, bulging cases heads, flattened primers, etc. __________________ Frohickey -- TFL Alumni SigSauer, if you are listening, MAKE A DOUBLE-STACK 10mm PISTOL!

May 8, 2002, 06:43 AM	#3
Khornet Senior Member Join Date: December 11, 2001 Location: NH Posts: 585	Redhook, When pressure is getting too high, two main primer signs are: "Cratering", which means that the indent from the firing pin develops a raised rim when primer metal flows into the gap between the firing pin tip and the rim of the firing pin hole in the bolt face. "Flattening", when the primer metal flows to fill the pocket completely so that there is no detectable groove between the primer and the rim of the pocket. Usually after firing there is still a little bit of radius left on the bottom of the primer's cup sothat if you drew a needle across the primer from its center toward the rim of the primer pocket it would fall into that little groove where primer metal meets case brass. Some say another sign is the appearance of the outline of the extractor cut raised in relief on the case head. __________________ The M1 does MY talking!

May 9, 2002, 10:42 AM	#5
KP95DAO Senior Member Join Date: December 30, 2000 Posts: 699	"Over pressurized brass." By "over pressurized" I take it you mean that the brass has been stressed beyond it's limits. There is only one reliable check for that. That is checking case head expansion at the solid portion surrounding the primer pocket. To do this you have to know the measurment before the firing. However a simple way is if the primers seat more easily than normal you have expanded the primer pocket and solid head. This is not where you want to operate repeatedly with a piece of brass. And by operating there you have removed all your safety margins. If some variable goes beyond the norm under these conditions you will have serious problems!!!!! A reliable test for excessive pressure with most all guns is "sticky extraction." Though this can be caused by a dirty chamber or a chamber with rough walls it is time to start looking for the cause if you run into this indication.

May 9, 2002, 02:31 PM	#7
Steve Smith Senior Member Join Date: December 9, 1999 Posts: 4,131	Flat primers can also me an indicator of a too-light load. Are you confused yet? __________________ Favor the X. Steve Smith NRA Life Member

May 8, 2002, 11:26 AM	#4
Poodleshooter Senior Member Join Date: August 7, 2000 Location: Floating down the James River in VA Posts: 2,599	Another quick way to check a case is to run your fingers down the sides of case, feeling for a slight dip down around the casehead, or just ahead of any belt. That may indicate a stretching casehead, when the presence of a shiny case or no primer may lead you to think that the case is relatively new.

May 9, 2002, 02:26 PM	#6
Chemistry Senior Member Join Date: September 23, 2001 Location: Central Alabama Posts: 158	Primer flattening may not necessarily be a true indicator of pressure. For example, when I load up some .45 ACP cartridges, using 230 grain FMJ, in combination with a 6.0 grain charge of Hodgdon Universal Clays, I get flattened primers if I use Federal primers (soft). If I use CCI primers (hard), there is no flattening.

May 9, 2002, 05:30 PM	#8
Mal H Staff Join Date: March 20, 1999 Location: Somewhere in the woods of Northern Virginia Posts: 16,955	The way a primer looks might be a good indicator of a high pressure excursion, but the only consistent indicator is the case head expansion KP95DAO mentioned. Either that or you could purchase about $70,000 worth of test equipment.

May 9, 2002, 06:30 PM	#9
C.R.Sam Senior Member Join Date: October 29, 1999 Location: Dewey, AZ Posts: 12,858	Mal speak true. Sam