Pressure signs-How to read for excessive pressure

RAThomas · May 17, 2007, 10:23 PM

What do you look for as an indication that the load is starting to too "hot"? I always believed that flattened primers was a tell tail sign. Now I am seeing flattened primers in commercially loaded ammo. I have yet to try any "P" loads, either +p, P++ or whatever. In developing a load, I do not load over the maximum listed for that caliber and do watch the fired shell for any signs.

Ry-guy · May 17, 2007, 10:29 PM

The primer will tell you alot. If it falls out of the shell that is generally a good sign that your pressure is getting to be to high. If you look at it after firing a normal load you will just see a dimple but if you see a little rise or wave around the dimple there is another sign of too much pressure because the primer is not only being hit by the firing pin but also being driven back into the pin from a hot load.

Hope that helps.

joneb · May 17, 2007, 10:48 PM

Aside from primer indicaters, stuck cases in the chamber would be another along with split cases and healthy brass.

dirty habit · May 18, 2007, 12:59 AM

Signs from primers can be a tricky business. Some primers are softer than others so while looking flattened, could be perfectly ok. I think you have to look at a combination of evidence before you can say excessive pressure.
Head expansion, sticky/hard bolt lift, excessive recoil/noise could all be signs you need to look for...

armedandsafe · May 18, 2007, 10:00 AM

I have a pistol which exhibits the ring around the firing pin dimple with factory ammo. I think it is caused by too large a firing pin access hole in the bolt. Factory agrees with me and I've not had any problem with hot loads (loading manual maximum -5%) in the gun.

Primers can also give pressure indications if you have too LOW powered a load. This gets tricky. Pressure signs from external changes in the fired case can give you a hint, but are not foolproof. One can always find a more clever fool.

Pops

**Unclenick** · May 18, 2007, 12:27 PM

No pressure sign is reliable by itself. You have to look for any of above, plus head expansion, side bulging, a load increment increase the doesn't increase velocity on your chronometer, etc. Which sign shows up first depends on the gun and cartridge. For example, you could have a flat primer from pressure, but you could also have it because your headspace is a little long. In the latter case, the initial pressure pushes the primer back, then chases it with the casehead (normal sequence in higher pressure rounds), the primer can first swell a little (mushrooming) before the casehead arrives, so the latter flattens the head of the mushroom. This occurs within normal pressure limits. The flat primer could also just be due to the primer brand having a thinner or softer cup than is best for the round.

Unfortunately the correlations to any one pressure sign are not good. Read Bramwell's article, here to see how Ken Waters' favorite sign didn't really pan out too well. Buying some pressure measuring gear is the only sure thing, but is a nuisance to use with any handgun but a single-shot pistol. I think most of us pick a load for best accuracy, and these loads seldom are all the way up at maximum pressure. Metal deformation by high pressure tends to work against accuracy. If your loads are getting way above published limits, that is a sign all by itself.

Nick

Trapper L · May 18, 2007, 02:11 PM

Click on the link, click on Informative Articles and click again on Primers and Pressues.
http://www.jamescalhoon.com/

Peter M. Eick · May 18, 2007, 03:44 PM

When you get a big puff of gas in the face and your hat blows off your head, then back it down a few grains.

I had that happen when a 243 rnd got mixed into a 708 reloading session and the load was on the edge for the 708 brass. The 243 was over the line.

**Mal H** · May 18, 2007, 03:48 PM

708?? 7mm-08?

**Unclenick** · May 18, 2007, 03:55 PM

Trapper,

I assume you meant the following page:

http://www.jamescalhoon.com/primers_and_pressure.php

The article goes right into a variant of the case head expansion measurements that the Bramwell article I linked to before proves is not a reliable correlation by itself. It is just one more possible pressure sign to track.

Nick

mrawesome22 · May 18, 2007, 05:11 PM

To me the best tool for knowing you are within acceptable pressure levels is the chronograph.

May 17, 2007, 10:23 PM	#1
RAThomas Senior Member Join Date: October 9, 1999 Location: Olathe, KS USA Posts: 129	Pressure signs-How to read for excessive pressure What do you look for as an indication that the load is starting to too "hot"? I always believed that flattened primers was a tell tail sign. Now I am seeing flattened primers in commercially loaded ammo. I have yet to try any "P" loads, either +p, P++ or whatever. In developing a load, I do not load over the maximum listed for that caliber and do watch the fired shell for any signs. __________________ If God had used the zero tolerance policy, there would be no human race. A house without a cat is just that - a house not a home.

May 18, 2007, 12:59 AM	#4
dirty habit Member Join Date: December 18, 2006 Location: New Zealand Posts: 57	Signs from primers can be a tricky business. Some primers are softer than others so while looking flattened, could be perfectly ok. I think you have to look at a combination of evidence before you can say excessive pressure. Head expansion, sticky/hard bolt lift, excessive recoil/noise could all be signs you need to look for... __________________ Happiness.......is a warm gun

May 18, 2007, 10:00 AM	#5
armedandsafe Senior Member Join Date: January 9, 2005 Location: Moses Lake WA Posts: 1,001	I have a pistol which exhibits the ring around the firing pin dimple with factory ammo. I think it is caused by too large a firing pin access hole in the bolt. Factory agrees with me and I've not had any problem with hot loads (loading manual maximum -5%) in the gun. Primers can also give pressure indications if you have too LOW powered a load. This gets tricky. Pressure signs from external changes in the fired case can give you a hint, but are not foolproof. One can always find a more clever fool. Pops __________________ Armed and Safe: Not just a theory If it time to bury them, it is time to dig them up. Remember, "Behind every blade of grass."

May 18, 2007, 12:27 PM	#6
Unclenick Staff Join Date: March 4, 2005 Location: Ohio Posts: 21,061	No pressure sign is reliable by itself. You have to look for any of above, plus head expansion, side bulging, a load increment increase the doesn't increase velocity on your chronometer, etc. Which sign shows up first depends on the gun and cartridge. For example, you could have a flat primer from pressure, but you could also have it because your headspace is a little long. In the latter case, the initial pressure pushes the primer back, then chases it with the casehead (normal sequence in higher pressure rounds), the primer can first swell a little (mushrooming) before the casehead arrives, so the latter flattens the head of the mushroom. This occurs within normal pressure limits. The flat primer could also just be due to the primer brand having a thinner or softer cup than is best for the round. Unfortunately the correlations to any one pressure sign are not good. Read Bramwell's article, here to see how Ken Waters' favorite sign didn't really pan out too well. Buying some pressure measuring gear is the only sure thing, but is a nuisance to use with any handgun but a single-shot pistol. I think most of us pick a load for best accuracy, and these loads seldom are all the way up at maximum pressure. Metal deformation by high pressure tends to work against accuracy. If your loads are getting way above published limits, that is a sign all by itself. Nick __________________ Gunsite Orange Hat Family Member CMP Certified GSM Master Instructor NRA Certified Rifle Instructor NRA Benefactor Member and Golden Eagle Last edited by Unclenick; May 18, 2007 at 03:47 PM. Reason: typo

May 18, 2007, 03:44 PM	#8
Peter M. Eick Senior Member Join Date: August 3, 1999 Location: Houston, Texas Posts: 2,991	When you get a big puff of gas in the face and your hat blows off your head, then back it down a few grains. I had that happen when a 243 rnd got mixed into a 708 reloading session and the load was on the edge for the 708 brass. The 243 was over the line. __________________ 10mm and 357sig, the best things to come along since the 38 super!

May 17, 2007, 10:29 PM	#2
Ry-guy Member Join Date: October 22, 2006 Location: Proud to be Canadian Posts: 47	The primer will tell you alot. If it falls out of the shell that is generally a good sign that your pressure is getting to be to high. If you look at it after firing a normal load you will just see a dimple but if you see a little rise or wave around the dimple there is another sign of too much pressure because the primer is not only being hit by the firing pin but also being driven back into the pin from a hot load. Hope that helps.

May 17, 2007, 10:48 PM	#3
joneb Senior Member Join Date: December 10, 2005 Location: Central , OR Posts: 1,888	Aside from primer indicaters, stuck cases in the chamber would be another along with split cases and healthy brass.

May 18, 2007, 02:11 PM	#7
Trapper L Senior Member Join Date: November 20, 2006 Location: South Texas Posts: 804	Click on the link, click on Informative Articles and click again on Primers and Pressues. http://www.jamescalhoon.com/

May 18, 2007, 03:48 PM	#9
Mal H Staff Join Date: March 20, 1999 Location: Somewhere in the woods of Northern Virginia Posts: 16,955	708?? 7mm-08?

May 18, 2007, 03:55 PM	#10
Unclenick Staff Join Date: March 4, 2005 Location: Ohio Posts: 21,061	Trapper, I assume you meant the following page: http://www.jamescalhoon.com/primers_and_pressure.php The article goes right into a variant of the case head expansion measurements that the Bramwell article I linked to before proves is not a reliable correlation by itself. It is just one more possible pressure sign to track. Nick __________________ Gunsite Orange Hat Family Member CMP Certified GSM Master Instructor NRA Certified Rifle Instructor NRA Benefactor Member and Golden Eagle

May 18, 2007, 05:11 PM	#11
mrawesome22 Senior Member Join Date: November 9, 2005 Location: Ohio, Appalachia's foothills. Posts: 3,779	To me the best tool for knowing you are within acceptable pressure levels is the chronograph.