Cratering/Piercing primers

Having a problem with my 223AI, figured I'd turn to the brain trust here.

Rifle is a 110 long action. Removed .473 bolt head and replaced it with a used OE Savage LA/.378 bolt head. Unfortunately for me, after doing this I started experiencing primer cratering & occasional piercing even with 'standard' loads that never showed pressure in any of my other 223 bolt guns. Switched from CCI-400s to CCI-450s, cratering & piercing went away.

Replaced the factory 223 tube with a Criterion 223AI barrel, and still occasionally see slightly cratered primers...but primer radius looks good and bolt swipe/lift/stickiness is normal. Yesterday, I blanked a few primers shooting a load I had shot many times before, and even popped a couple primers which caused me to stop shooting.

Other than verifying the quality of my loads...

Should I check firing pin protrusion? I did not do that when I swapped bolt heads.

Should I consider having the firing pin hole bushed, or replacing the firing pin itself? The firing pin started life as 270 Win, and the bolt head came off a rifle of similar vintage...

Thanks

I need to think beforeI post.

Quote:

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Originally Posted by stangfish

Check headspace on your sized cases by using a shim behind the head or partialy seat a primer and close the bolt.

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Then check firing pin protrusion. Especially if you did a bolt head change. They're not all the exact same dimensions.

Don't ask me how I know that.

Cratering can be caused by a few different problems. First thing to check is the shape of the firing pin, it is possible once you blank a primer to misshape the firing pin, and cause repeated cratering problem. Make sure the bolt head is free of brass, and other obstructions. Have you don't anything to the firing pin spring? Some people like to cut coils, or put spacers behind the BAS for a gunk button, and other strange things, primer cratering is caused by the firing pin not being supported. If you have put the rifle back to stock with a proper spring check for tension. After you have checked all of these things, then look into having the firing pin hole brushed. It is possible that the firing pin is smaller than the hole, causing this problem. Unfortunately savage has large tolerance ranges, and parts can be one side or the other. Also when you blank primers, it is possible to flam cut this hole out of round, and make it larger. Something else that comes to mind is that savage did change the firing pin diameter throughout the years, but the tip (What matters in this case.) is the same size.

Typically createring with a OE firing pin is due tip profile.

As you may have heard (or not) you'll never indent a primer more than .020"-.022" regardless what the bench protrusion is set to. Typically the indentation is around .016-018" or at least those I've measured.

Unfortunately the factory pin tip is ground on more of a taper which extends back from the tip to the shank about .025" or a tad more which allows a gap between the tip and pin hole when striking a primer. Its also why the CCIs with their thicker cups didn't creater or blank, they are less prone to flow into the gap.

The "fix" is to re-profile the tip to a radius.

http://i47.tinypic.com/3096838.jpg

On the left is factory, on the right one I re-ground to a radius which is about 1/2 the length from the tip to the shank.

The same pins set for .020" protrusion in the same bolthead, the factory profile on the left, and the re-ground one on the right.

http://i50.tinypic.com/2ur0aaw.jpg http://i48.tinypic.com/2e3oq5s.jpg

Now, your next question how much? I don't know. It was trial and error until I got it and my gauge right and haven't bothered actually measuring it! I start grinding until the tip matches the gauge and call it good.

Bill

GREAT POST BILL PA!!!!
I think that explains it well.

Whether you realize or accept it, the .223 AI is operating at higher pressure. It doesn't show it like a standard case because of the case taper is less and it has less bolt thrust.

Quote:

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Originally Posted by sharpshooter

Whether you realize or accept it, the .223 AI is operating at higher pressure. It doesn't show it like a standard case because of the case taper is less and it has less bolt thrust.

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I both recognize and accept both as facts, both of the Ackley design and the way I previously loaded for it.

Everybody wants "maximum warp" but for safety and brass longevity I'm going to have to find a lower accuracy node and live with it.

I can't "blame" the primer issues solely on a hotly loaded 223AI though, as I experienced cratering/blanking using a standard 12FV 223 barrel on the 110 long action with LA/378 bolt head using the fairly common 75gr HPBT/24.0gr Varget/CCI-400 load, which I shot thorough the same barrel without issues using a 12FV short action. Switching to CCI-450s stopped the cratering/piercing issue in that barrel on that action, but it seems to me harder primers aren't really "fixing" the problem.

I had the same problem with my .223 If your firing pin protrusion is within spec you might want to get a bushing installed. Or you can try a bolt head from ptg. Thats what fixed it for me.

What is blanking a primer?

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Originally Posted by jonbearman

What is blanking a primer?

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When a primer craters so much that it pops, and all the gas come rushing out the primer hole.

Disassembled the bolt tonight...firing pin tip looks good, same as the left side in Bill's picture above. Measured firing pin protrusion at .058...made an adjustment and its now .033. Empty piece of brass made a primer go BANG, so I guess that's good.

Might not be the cure, but certainly shouldn't hurt...probably will end up ordering a PTG LA .378 bolt head to see if that fixes the issue, and if not, the next step might be holding my breath and grinding a new radius on the firing pin tip.