To much pressure? Back off on the powder charge? Ten grains? 

Bullet weight? BS or fixed??


                     Joe.

thanks for the replies  that high pressure was my first thought, the darn things shoot really good too. i am in the process of making some cases from starline brass and some maximum brass then i will back off the grains and see what happens. this is my first experience with soft(?) fed brass. usually fed is pretty good  thanks again !

Starline also makes .360 dan Wesson cases. They appear to have a thicker web

I am shooting my 32-30 IMP not a Miller short but my study on the .357 based cases is that there is very little difference between any of them. 
  My experience with Remington .357 Max brass is that it needs to be lightly annealed to form properly. I would rough trim the cases then put them in water leaving about .300” out of the water. Lightly run the torch over the case necks and tip them over into the water. This will keep the heat from traveling down into the web and base.
  Second a powder change may be in order shooters are getting better results with 4100/Enforcer or #9 than 4227 with .357 based cases.
  Third you don’t mention what the twist of the barrel or the weight of the bullet is. I started off using a 230 gr. Borton bullet I also tried a 230 gr. Jones mold both gave me accuracy but I was getting case sticking after five shots or so. I went to David Mos and had a 216 gr. bullet made to fit my throating. The shorter bullet let me back off on the powder a little and still get optimum performance. I can now shoot all day with one case. 
  Lastly get yourself some 5.6 X 50R Magnum brass. The RWS is hideously expensive but it is just plain better brass. You can form it fully without annealing and I haven’t lost a case in three years.

40 Rod   

Shooting plain base bullets, I find it hard to believe that pressures are ever high enough to loosen primer pockets or stick cases.  The pressure required to get a 230 grain bullet to 1450 fps out of a 24 inch barrel is about 25,000 psi, regardless of the case size.  

I have fired dozens of rounds of .357 Max in my T/C, loaded  to just short of 40,000 psi, as do hundreds if not thousands of other guys using the Max for deer.  Nobody has reported any trouble with the brass.   Something does not compute.  

Is it possible that, in forming the Miller case, the brass was too much annealed?  

Can somebody tell me what the case capacity (preferably in grains of water) is for the Miller?   I'd like to run some models in Quickload. 

That makes it easy.  Thanks.

The 12 grains of 4227, 230 grain bullet breech seated, should yield about 20,000 psi and 1300 fps from a 24" barrel.

Raising that charge to 14.7 grains runs the pressure up to around 31.5k psi, and 1550 feet per second.   

Hope that helps.

headspace is fine. i formed 20 new max cases to 32 miller and the primers went in very firmly. the primer pockets are a trifle smaller than the federal cases. have not shot them yet    i did not know about the quickload and how to use it but that looks like a good tool    thanks again