Need help with 308


April 17, 2009, 10:44 AM
I've recently bought some military 308 brass to use and am having some problems with it. After processing the brass and loading it,using the same procedure as I do with commerical brass, it fits very tight into my chamber so tight that I almost can't lock the bolt down. Thinking that it may need to be fire formed to fit my chamber I went to the range and after firing it it stills fits pretty snug. With the commerical brass I have no problems at all either before or after firing it. My thoughts are that because it's military brass the neck may need to be turned some to reduce the thinkness at the neck. Anybody have any other thoughts on what maybe the cause of this?

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April 17, 2009, 10:51 AM
My guess is you're neck sizing only.
Any brass fired in a different weapon would need to be full-resized and then fire formed to fit your chamber.

April 17, 2009, 11:04 AM
Military brass is usually thicker than commercial brass and you may have a close to minimum spec chamber, which is good.
Smoke a case after sizing with a candle or use a marker pen on it to see where it's tight as it will shine the brass where it's touching. Then you can decide how to approach a fix for the issue.
It will either entail sizing the cases a bit deeper if it's near the base, or as you mentioned, turning the necks if it's tight there, or both.
You are full length sizing, correct?

April 17, 2009, 11:29 AM
Also, if fired from a chamber on the loose side (not uncommon for a MG), the case may have streched and after full length resizing need to be trimmed quite a bit.

I have never had to turn the necks of military brass to function in any of my bolt guns.

April 17, 2009, 11:34 AM
If the cases are an interference fit, shooting them seldom makes them smaller.

When cases are fired they get larger. So does the chamber. After the pressure drops, the chamber is back to normal dimensions, and the case shrinks a little due to springback. If your case was an interference fit to begin with, when it "springs back", you will often have even more of an interference fit.

This is another example of not using a case gage to set up your sizing dies. At best you are following the "size to the shellholder and add an eighth turn". This advice is so bogus. :cuss:

At a minimum, buy a cartridge case gage and size to gage minimum. You will find that pot luck, once fired cases, don't necessarily size to gage minimum. That's why I keep a case gage on the bench and check mystery brass. If the stuff comes out too large, I set my small base die to size a bit more.

Also, I will bet that you are using standard sizing dies.

Here is an example of two military cases fired in a Zepplin sized chamber. One the left is a Wilson gage, on the right a reamer cut gage. The reamer cut gage was a barrel stub cut to depth with a chambering reamer. (My gunsmith did this for $35.00) The Wilson gage only measures length, but the reamer cut chamber will tell me if my cases are too long, and "too fat".

One case sized in a standard sizing die: It is an interference fit after sizing.

The other case sized in this Small Base die: It drops in all the way.

You will find examples of brass fired in chambers so large, that even a small base die won't bring them back.

April 17, 2009, 11:38 AM
Take a fired unsized case and see if a bullet will slip back in it freely.

If it will, neck thickness is not the problem.
And I would be amazed if it was!

GI brass is harder & thicker then most commercial brass.

More then likely, you don't have the sizing die adjusted down enough to take all the spring & linkage slop out with the harder GI brass.

Screw it down until it touches the shell holder, then screw it down another 1/8 - 1/4 turn until you feel a definite "bump" when the linkage cams over.


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