I don't know where to go next. I have a 6mm AI built on a model 98 Mauser action. McGowan Rifles did all the work. I bought 3 boxes of Remington 6mm Rem. bullets to fire form in the gun. I had quite a few of them get hairline cracks in them. I did not notice that until I went to resize them and one of them broke off in the resize die. After getting the dies back from RCBS I tried a few more and broke one off again. I inspected all of the remington brass I had for hairline cracks and threw them in the trash. The next time I bought shells I bought Federal instead. I am still getting hairline cracks in the cases and now one of them broke off in the chamber. I have some brass that seem to be OK. I have tried several different loads over the past year and I still get some cracking in the cases. There is no relationship the the amount of powder in the load and if it will crack or not. I have checked for any signs of high pressure in the loads but have not seen any(Flattened Primes, Case web expansion, etc). The crack on most of the brass is about 1/2" up from the base however some times it is closer to the head. McGowans are sure that there is nothing that could have been caused by them. I am perplexed and am in desperate need of some help. I have a few other calibers I fire form for and have never had a bit of troouble with them.

I don't know allot about the 6mmAI but what I would do is purchase some new brass, anneal the necks, then load with a mid range load and fire form them. this hould take care of the cracking or spliting. After they have been fire formed the next reloading I would neck size them, load and go to the range.

Hmm Is there a production date on the ammo box? Wonder if it is loaded up close to where it should be, and the brass is of older stock?

If you have any more factory loads from that batch, try pulling bullets and loading down..

That or buy new brass in bulk. This way you can work on brass from the same run, and work up loads.

Need more input...

Are these cases ALL reloads, or is this occuring with factory ammo as well?

What do you mean by breaking off? That sounds like more than a split neck... Are you getting ruptured cases? If so, STOP SHOOTING IT!! That is extremly dangerous...

It is tough to pinpoint what is going on with the limited info here, but this is sounding like one of three things.

A- a problem with the chamber.

B- A reloading error.

or C- a die problem.

The cracks in the cases usually go around the circumferance of the case. This is why I thought I had a chamber problem at first. I have had factory rounds crack however this was during the fire forming process. I usually full length resize the cases. I always start of on the low end of the reloading data I have and work up. The rounds I tried today were H1000, 52,53,54 grains. That info came from this web site. WHat other information would you like?

Quinn:

What you have sounds like case speration due to too much brass stretch. A chamber with the shoulder too far forward would certainly cause this problem. Have your gunsmithing firm do a chamber cast for you, and them. That will answer a lot of questions, and hopefully solve your problem.

Good Luck

Jerry