Test loads in March fine, but July raising firing pin dents?

A place to discuss calibers, ammunition, and reloading

Test loads in March fine, but July raising firing pin dents?

Postby EJSG19 on Wed Jun 27, 2018 11:14 pm

I've got a Patriot Ordnance 308 Edge SPR I'm developing loads for. An odd thing for me happened this afternoon. I began testing for this rifle with Sierra 180gr Pro Hunters on IMR 4895. Loads only 2/3 the way up the Hornady manual powder charge range was where I stopped at that time, and no pressure signs on the case or primer ever showed up, and Chronograph speeds were as expected.

Now, fast forward to today in July, about 25 degrees warmer outside (though I didn't let the rounds sit in the sun and get hot, they were cool to the touch upon loading into the rifle.) Same exact process followed, however today, every test load below, equal, and above those powder charge levels had a puckered firing pin divot show on the primer cups.

I thought this might be due to the 25 degree warmer temperature, so I put 5 rounds in a cooler on ice, waited for them to be very cold, loaded, fired, same result on the primer, a puckered or raised up ring right around the firing pin. The rest of the primer does not appear flattened, just that raised ridge around the firing pin dent.

Any good ideas as to what I'm doing that is giving me this different result? I'm out of ideas and a bit frustrated/stumped. This rifle appears to dislike loads toward max charge which seems pretty odd. It does have a 3 position gas block which I've triple ensured is set to the correct setting.

Brass is brand new Starline 308 brass. Primers are Winchester Large Rifle. IMR 4895 powder (again, only 2/3 the way up to maximum charge in Hornady manual. ((Lyman manual says to go even hotter)

Thanks.
EJSG19


"Cum catapultae proscriptae erunt tum soli proscript catapultas habebunt."
User avatar
EJSG19
 
Posts: 3931 [View]
Joined: Mon Oct 27, 2008 3:31 pm
Location: Greene Co, IA

Re: Test loads in March fine, but July raising firing pin dents?

Postby Rip Van Winkle on Thu Jun 28, 2018 5:06 am

There's 2 causes for cratered primers. one is over pressure, the other, and more common, is an oversized firing pin hole.

As long as your charge weight of 4895 is below ~43gr, I don't think that'd be the problem. Are you getting any kind of dimples on the case head?

2 suggestions before you do anything else. 1) Try a different brand of primer. Winchester primers are on the soft side. Try CCI or Remington. 2) Make sure your rifle is clean, especially in the lead of the chamber. Sometimes carbon can gather in the lead of the chamber causing a carbon ring.
I will never apologize for being an American.
Post 435 Gun Club
North Star Rifle Club
cmpofficer@post435gunclub.org
48 down, Still in the hunt for a heavy!
President's Hundred (#48 2018)
Certified NRA RSO
User avatar
Rip Van Winkle
 
Posts: 4165 [View]
Joined: Thu Jul 26, 2007 5:04 pm
Location: Unfashionable end of the western spiral arm, Galaxy Milky Way

Re: Test loads in March fine, but July raising firing pin dents?

Postby EJSG19 on Thu Jun 28, 2018 6:05 am

Rip Van Winkle wrote:There's 2 causes for cratered primers. one is over pressure, the other, and more common, is an oversized firing pin hole.

As long as your charge weight of 4895 is below ~43gr, I don't think that'd be the problem. Are you getting any kind of dimples on the case head?

2 suggestions before you do anything else. 1) Try a different brand of primer. Winchester primers are on the soft side. Try CCI or Remington. 2) Make sure your rifle is clean, especially in the lead of the chamber. Sometimes carbon can gather in the lead of the chamber causing a carbon ring.


Thank you Rip, I will explore those two items. Could be chamber dirty. These would be rounds 45 or 50 since being new, and I don't believe I chamber brushed it when I received it which now that I think about it has me questioning my common sense levels.

Yes, what is striking me as odd is that these signs are occuring at charges of 39 and 40 grains, when Hornady says max is 41.1 and Lyman says 43.5. (going from memory, not looking at manual right now.)
EJSG19


"Cum catapultae proscriptae erunt tum soli proscript catapultas habebunt."
User avatar
EJSG19
 
Posts: 3931 [View]
Joined: Mon Oct 27, 2008 3:31 pm
Location: Greene Co, IA

Re: Test loads in March fine, but July raising firing pin dents?

Postby Rip Van Winkle on Thu Jun 28, 2018 7:19 am

I doubt you would be dealing with a carbon ring at 50 rounds, but maybe you have a rough spot in the lead of the bore. A good cleaning would be a good first step. I'd recommend a good scrubbing with some JB Bore Paste.

If you still have problems after a good cleaning and switching primers, I'd start looking for a new firing pin and bolt.
I will never apologize for being an American.
Post 435 Gun Club
North Star Rifle Club
cmpofficer@post435gunclub.org
48 down, Still in the hunt for a heavy!
President's Hundred (#48 2018)
Certified NRA RSO
User avatar
Rip Van Winkle
 
Posts: 4165 [View]
Joined: Thu Jul 26, 2007 5:04 pm
Location: Unfashionable end of the western spiral arm, Galaxy Milky Way

Re: Test loads in March fine, but July raising firing pin dents?

Postby EJSG19 on Thu Jun 28, 2018 1:10 pm

Rip Van Winkle wrote:I doubt you would be dealing with a carbon ring at 50 rounds, but maybe you have a rough spot in the lead of the bore. A good cleaning would be a good first step. I'd recommend a good scrubbing with some JB Bore Paste.

If you still have problems after a good cleaning and switching primers, I'd start looking for a new firing pin and bolt.


While giving the rifle a good cleaning, I called Patriot Ordnance.

Tech claims they manufacture their bolts with a tolerance between the firing pin and the bolt face hole, and that shooting heavy grain high pressure loads would not be uncommon to see such signs on the primer. I do see maybe a slight gap between firing pin tip and bolt face hole, but very small. I suppose under chamber pressure levels that could be enough to see what I'm seeing. Still doesn't explain why I saw nothing of the sort in March of this year, and I'm seeing it now, even with lower powder charges than I shot fine in March.

Hmm. POF says go for it, while warning me not to shoot 1000's of rounds of heavy grain high pressure ammo or it'll cause faster than normal wear.(no kidding?!? I thought.)

According to him, he'd shoot as much as necessary to hunt. I think I'd be wise to find a harder primer if so.
EJSG19


"Cum catapultae proscriptae erunt tum soli proscript catapultas habebunt."
User avatar
EJSG19
 
Posts: 3931 [View]
Joined: Mon Oct 27, 2008 3:31 pm
Location: Greene Co, IA


Return to Ammunition & Reloading

Who is online

Users browsing this forum: No registered users and 11 guests

cron