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243AI case splitting problem when fire forming

 
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  #1  
Old 08-10-2004, 09:58 AM
BLD BLD is offline
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243AI case splitting problem when fire forming

I had a small hole about 1/4" above the head of the case form when fire forming new factory lapua loads. After about a dozen loads like this it burned a hole in my chamber. I had the barrell shortened and rechambered. Now the same problem is happening. The cases have the same exact shape hole and in the exact same spot both before the rechamber and after. Note: not every single case formed does it, ~ 80% do. I am wondering if I should empty and reload the factories with cream of wheat loads? Could I just have a bad batch of lapua's? Also not the case has a small bulge on the opposite side of the case and the hole is about the size of the shaft of a pin. I don't want to ruin the barrel again. I have not had a reloaded shell do this yet. Any help is very much appreciated!
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Old 08-10-2004, 12:25 PM
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Re: 243AI case splitting problem when fire forming

BDL,

When you chamber a virgin round to fireform, do you feel the crush fit when the bolt is locked down.

If chambered correctly, there should be 0.004" to 0.005" crush fit on the shoulder of the virgin case to prevent case strecthing.

If you do not feel this noticable increase in pressure to close the bolt, your rifle is not chambered correctly for the AI round.

The result will be excessive case strectching and in severe cases, case seperation just ahead of the solid case head.

Something to look at anyway.

Good Shooting!!

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Old 08-10-2004, 01:27 PM
LB LB is offline
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Re: 243AI case splitting problem when fire forming

The best and most efficient method I have used, to fireform new brass in an Ackley chamber is with a "loaner" rifle and a junk barrel, the chamber of which, cut with the same(!) reamer as your gun. Fast, and without any throat errosion (wear) on your premium barrel. The loads should be somewhat less than max, and the shoulders will be at least 80% formed. Anyway, works for me.

If you know how to check for incipient case head separation with a sharp wire, bent at 90, that should tell you if your gunsmith is unfamiliar with this type of work. You can feel the developing crack just ahead of the web. If that's the situation, you are lucky not to be leaving the entire case body in the chamber as you extract the head.

You might want to seek an alternate craftsman, for an opinion.

Good hunting. LB
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Old 08-10-2004, 11:36 PM
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Re: 243AI case splitting problem when fire forming

Email Janne at lapua before you fire another shot--I think i heard of this problem on another board?? might have been you there as well??

Janne's email--> janne.pohjoispaa@ nammo.fi

JB
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  #5  
Old 08-11-2004, 02:53 AM
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Re: 243AI case splitting problem when fire forming

Never heard such a thing fire formed many hundred Lupua 243 brass and only had about 2 that did not form right.
http://www.pbase.com/m16800/toys

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Old 08-11-2004, 03:27 PM
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Re: 243AI case splitting problem when fire forming

I have a couple of AI carts. I fireform. The closest to what you have is a 244 AK. I begin with a 6mm Rem, load it near max, seat the bullet shallow so it jams the bullet into the lands forcing the case base into the bolt face and light it with an RP 9 1/2 mag primer. Results in a perfectly formed case. This is in a very tight chamber too. Never heard of anything like you have... [img]images/icons/confused.gif[/img]
db
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Old 08-11-2004, 04:17 PM
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Re: 243AI case splitting problem when fire forming

dbholster,

When properly chambered liek the way I do teh AI rounds and the way any top smith better chameber them, there is no need at all to seat the bullets into the rifling.

In fact all this does is create the possiblility for pressure problems.

With a proper 0.004" to 0.005" crush fit in the shoulder, the case is supported by the chamber and simple can not stretch forward.

Your chamber is probably chambered correctly, if it is then on virgin brass you should be able to chamber a round and feel that slight crush of the shoulder, you should also be able to chamber a round and then eject it and visually see a bright line around the neck/shoulder junction which is the crush line.

This is all you need for proper case control and when chambered this way, my rifles will generally average in the 1/2 moa with virgin brass.

I'm not questioning your loading technique at all, just that if your rifle is chambered correctly, which it probably is, you do not need to seat the bullets into the lands.

Good Shooting!!!

Kirby Allen(50)
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Home of the Allen Magnum, Allen Xpress and Allen Tactical Wildcats and the Painkiller Muzzle brakes.

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