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Old April 9, 2007, 08:59 PM   #1
x5shooter
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Problem with 308 brass body growth

I have a 308 with a match chamber. When measuring the case body at the thickest part towards the bottom i get:

New unfired 308 case .464
Fired case .470

is it normal for a match chamber to allow a case to grow this much? I have been just neck sizing and it has been working fine, i went and tried to FL size the brass and got the first case stuck, it was very hard going in even with lots of lube. Has the case grown too much to be resized? Can i use rounds that i neck size only in other guns or will the case get stuck? I am a bit puzzled, thanks guys.
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Old April 9, 2007, 09:30 PM   #2
Shoney
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According to my data sheet, 0.470 is the correct diameter of the base. The following site also confirms this dimension,
http://ammoguide.com/?catid=92
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Old April 10, 2007, 12:50 AM   #3
Paul B.
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X5Shooter. Everything looks OK to me. As you have just been neck sizing, therein lies the problem. I don't know how many times you neck sized that brass prior ro trying a full length resize, but what I do is after the first firing, I trim the brass and neck size for a total of four reloadings. Then, I anneal the necks and do the full length size for the fifth reload. The only .308 I have that has anywhere near a match chamber is my Savage 110S silhouette rifle. I have to do the full length resize and anneal on the third reloading for that rifle. You'll have to experiment a bit for your rifle to determine when you have to anneal abd F/L size the brass.
What has happened is when you fire that round, the case expanded to fill the chamber. When it shrinks back down after the pressure has dropped, it does not go back to it's original dimensions. it's a tad fatter than when it started out. You neck size, load and fire and the same thing occurs, only this time it's even fatter. This continues until the case is literally too large to chamber properly. Now in all this neck sizing, the neck has become quite work hardened. If you do not anneal the necks, they will shortly split. It's kind of like bending a wire coat hanger back and forth until it breaks. By annealing the necks, you can at least double the life of that brass and possibly even more.
I have one box of old .375 H&H brass that I use strictly for a cast bullet load. it's fairly stiff with recoil a bit stiffer than a hot loaded 30-06. The bullets get a very tight crimp. By using the method described above, I have gotten 20 reloads from those cases. I usually check case length at each reload and trim as necessary.
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Old April 10, 2007, 09:00 AM   #4
Abstract
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Quote:
I have a 308 with a match chamber. When measuring the case body at the thickest part towards the bottom i get:
What kind of .308 do you have with a "match" chamber? (Just curious!)

If you lube and set up your f.l. sizing die properly, you won't get a case stuck in the die, regardless of how many times you've neck-sized the case. Your cases have been "fireformed" to your chamber; they may or may not work in another rifle's chamber.
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Old April 10, 2007, 11:51 PM   #5
x5shooter
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ok thanks guys that explains it. The rifle is a GA Precision with their chamber. Thanks again.
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Old April 11, 2007, 02:01 AM   #6
James A. Mullins
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Just one question. Do you have any trouble extracting after firing? Any case will expand to the size of the chamber. As long as you can easely extract the case you don't have a problem. Just check the length and as long as they don't grow past max. length Your ok. There is no way brass can expand after you extract from the chamber. Your GA chamber is to thier specs. You should also use a paper clip with a small 90% bend to check inside the cases for cracking. You will notice gross ovl before you feel any crack. As long as you use the same gun you shouldn't have a problem.
Good luck.
James
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