Enlarged primer pockets, all of a sudden

P

P. Octo

Member
A friend's rifle suddenly started to produce enlarged primer pockets:
It is a 6PPC Panda, with a barrel that has shot over 4000 rounds of FB 68 gr on top of 29,16 gr of 133 shot just above sea level and in températures between 16 and 25°C, this with 2 different lots of Lapua cases, 2 different lots of powder (I mean since the problem appeared). Bullets measure correctly at .2433 at the pressure ring, loaded cartridge at .2610 for a .262 chamber; length of cartridge ok: no overlong neck being crimped in the cone. It had been shooting quite well with no pressure signs until last month, then after a couple of shooting, the primers could be inserted by hand or would even drop out if you turned the case over!
Yesterday, we went to check it out and I used my chronograph to measure its velocity: a surprising 1056m/s (3460 ft/s) and obvious signs of pressure on the primers: deep cratering and the metal around the rim of the primer looked as if it had flowed, become liquid. I haven't got a borescope but we took care of cleaning as best as we could, with Carbon Killer, the leade in case it could be due to a carbon ring.
I am at aloss to explain. I realise fully that without a borescope it's hopeless to be sure, but I would welcome your suggestions. BTW, this particular shooter has over 20 years experience and has been a top shooter in Europe with half a dozen different BR rifles.
Looking forward to your input.
 
Three things:
I have never had a hard carbon problem with 133 (which I have used for over 15 years), and my barrels have been inspected with bore scopes. I generally clean with Butch's, patches, and bronze brushes. Having said that, I believe that if I suspected a carbon problem, that was causing the kind of pressure that your friend is experiencing, that I would go straight to IOSSO on a nylon brush as my preferred remedy. Back when Tony Boyer was shooting T powder, which was known to have carbon issues, he recommended short stroking a brush (I prefer a softer, black one for this.) in the back 8-10" of the barrel, starting with the brush fully loaded, and using a larger diameter brush in the neck, running it up to the end, and spinning it. We have used the same technique in the back half to two thirds of barrels that had more carbon and which used slower powders. With that high of a round count, I would expect that the throat of that barrel would be showing considerable "alligatoring" and my experience with that is that its abrasiveness will cause jacket fouling which can pile up pretty quickly. One method that you can use, if you lack a bore scope, is to carefully slug the barrel, with a pure lead slug. That will allow you to feel any constriction. Let us know what you discover about the cause of this.
 
Boyd,
Thanks for your opinion; we'll try the IOSSO treatment. I hadn't thought about 'alligatoring' and copper pile-up: we'll put that on the "Usual Suspects" list!
Best regards.
 
Brass

Could it be that your lapua brass is just worn out from repeated firings. You don't mention brass reload counts.

One instant fix might be a new barrel. A 6PPC barrel that's got 4000 rounds through it, may not be worth the effort to try to fix a problem with brass primer pockets.




Glenn
 
Enlarged primer pockets - N133

Phillipe I shoot N133 since 1991 after the WBC in Fréjus and never, repeat, never, have seen 29,2 grainds even of the fastest lots (2007) producing 3460 FPS with a 68 grain bullet, in a PPC barrel, there must be something with your friend's N133, a mix with N130?
Please ask your friend to check his powder and try his rifle with a known charge of your own known powder lot and check the speed on the chronograph.
 
Thank you all.
The rifle has shot at the top of European matches for quite some time - and still shoots well.
The brass was 3 matches old for the first lot and new for the second lot (Rohn Hoehn)
Carlos, We did try 2 different lots of 133 and the reason I posted was because I was flabbergasted by the velocity and pressure signs, but I get your point and will try with my own lot. BTW, the chronograph was used first on my rifle and worked as advertised: after all, it could have been that too.
The strange thing is that this phenomenon appeared all of a sudden and we suspected a bad lot of brass at first, something akin to what happened to another shooter but that's another story.
I think we will try to make sure there isn't any ring, carbon or brass, as suggested by Boyd and then proceed with powder tests.
'Affaire à suivre', as we say over here.
 
I'm sure this is obvious, but do you feel some resistance when closing the bolt? Reason I ask is, I've checked a lot of barrels and have NEVER seen even one produce crazy pressure from (wear/firecracking/"alligatoring"/carbon buildup/dirty bore/over-sized bullets/under-sized bullets/twist rate/etc/etc) but only from either over-long cases or a carbon buildup which causes the caseneck to actually crimp onto the bullet.

Bore friction is simply too small a factor IMO

al
 
alinwa said:
I'm sure this is obvious, but do you feel some resistance when closing the bolt? Reason I ask is, I've checked a lot of barrels and have NEVER seen even one produce crazy pressure from (wear/firecracking/"alligatoring"/carbon buildup/dirty bore/over-sized bullets/under-sized bullets/twist rate/etc/etc) but only from either over-long cases or a carbon buildup which causes the caseneck to actually crimp onto the bullet.

Bore friction is simply too small a factor IMO
Alinwa, no problem closing the bolt; checked the OAL and had trouble finding the marks on the bullet with a x12 magnifying glass. They were there, all right, but faint, squarish and, yes, corresponding to the number of grooves. No obvious sign of crimp either. But as the devil is in the détails, we thought about all that has been expressed here, we looked and didn't see anything glaring at us but didn't do a thorough check. So your suggestions are gratefully appreciated, duly noted and will implemented as soons as planning permits.
Click to expand...
Click to expand...
 
Test

Have you tried reducing your 133 powder charge,using the new lot of brass,to see what happens to primer pockets.




Glenn
 
not overall length, loaded neck diameter. important difference.

if you have a barrel stub cut with the reamer it is easy to check to see if there is a fat neck.
 
ray porter said:
not overall length, loaded neck diameter. important difference.

if you have a barrel stub cut with the reamer it is easy to check to see if there is a fat neck.
Click to expand...

I asked him to take the barrel out so that I can measure the actual chamber & neck diameter against the advertised one, just to be absolutely sure, but as I wrote in the original description the rounds measure .2610 for a .262 advertised diameter and as the problem appeared during a match where nothing had been altered, I guess this possibility isn't at the top of the list.
 
P. Octo said:
I asked him to take the barrel out so that I can measure the actual chamber & neck diameter against the advertised one, just to be absolutely sure, but as I wrote in the original description the rounds measure .2610 for a .262 advertised diameter and as the problem appeared during a match where nothing had been altered, I guess this possibility isn't at the top of the list.
Click to expand...

Sorry, I missed where you stated the loaded neck diameter in the OP

Tim
 
A complete aside.... in the op was mentioned "cleaning with Carbon Killer."

If this is the product Slips 2000 Carbon Killer and if the problem IS carbon buildup, then maybe it needs time to work. I used Slips Carbon Killer for wiping casenecks and for attacking the carbon ring and found it about as efficacious as spit on a rag.....useless.

Others have touted soaking overnight and that it's wondrous fine.

I've never done this, I set the stuff on my shelf where it forthwith separated into several perty layers of liquid....and there it sets to this day.
 
alinwa said:
A complete aside.... in the op was mentioned "cleaning with Carbon Killer."

If this is the product Slips 2000 Carbon Killer and if the problem IS carbon buildup, then maybe it needs time to work. I used Slips Carbon Killer for wiping casenecks and for attacking the carbon ring and found it about as efficacious as spit on a rag.....useless.

Others have touted soaking overnight and that it's wondrous fine.

I've never done this, I set the stuff on my shelf where it forthwith separated into several perty layers of liquid....and there it sets to this day.
Click to expand...

Yes, it is and if yes, he'll try Boyd's suggestion with IOSSO. I am using Carbon Killer after every series, just one patch followed by a dry one, but I am shooting moly and whenever I checked with a borescope the leade, neck & all was clean. But let's not start a cleaning thread!
 
I would bet that a new barrel would solve the problem. I take my 6ppc barrels and put them on a varmit gun (I have a varmit gun with the same custom action) and I shoot the dog out of them. What your describing is a fouling/carbon problem. Here is how to diagnosis where it is:

After cleaning the gun, shoot it over a chrono: you will see one of two things.

1. If the velocity immediately wants to travel north of 3400 with that load. The carbon fouling is a ring at the end of the chamber and is pinching the case neck. You won't notice much difference, if any in bolt closing but shooting .001 clearance makes it easier to happen.

2. If the velocity starts out fairly normally and climbs to 3400+ in around 8 rounds or so (maybe more), then the carbon/copper is adhering to the aligatoring/fire cracking in the first few inches of the barrel.

Sad truth is, both of these is a death blow to a barrel once it's got a lot of rounds on it.

You can try on more thing, take some brass and trim it way back, say 2.460 inches and see if the velocity drops back quite a bit (100 fps or so) for several rounds. That shows the build up around the neck.

I've had both these situations happen and Ed Watson told me what was going on (before bore scopes). He was dead on.

Hovis
 
HovisKM said:
I would bet that a new barrel would solve the problem. I take my 6ppc barrels and put them on a varmit gun (I have a varmit gun with the same custom action) and I shoot the dog out of them. What your describing is a fouling/carbon problem. Here is how to diagnosis where it is:

After cleaning the gun, shoot it over a chrono: you will see one of two things.

1. If the velocity immediately wants to travel north of 3400 with that load. The carbon fouling is a ring at the end of the chamber and is pinching the case neck. You won't notice much difference, if any in bolt closing but shooting .001 clearance makes it easier to happen.

2. If the velocity starts out fairly normally and climbs to 3400+ in around 8 rounds or so (maybe more), then the carbon/copper is adhering to the aligatoring/fire cracking in the first few inches of the barrel.

Sad truth is, both of these is a death blow to a barrel once it's got a lot of rounds on it.

You can try on more thing, take some brass and trim it way back, say 2.460 inches and see if the velocity drops back quite a bit (100 fps or so) for several rounds. That shows the build up around the neck.

I've had both these situations happen and Ed Watson told me what was going on (before bore scopes). He was dead on.

Hovis
Click to expand...

Yes, that's seems to be the case (no pun intended). We'll have a look as soon as we can lay our hands on a borescope but I reckon it's time to lay it to a well deserved rest...
 
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