Anealing the mouths will probably solve the problem.

Breech seating the bullets also.

I have been having blow back issues with the sloppy chamber in my Ballard so I annealed a few cases and flared the case mouths every shot at my last outing on Monday.  It made a big difference.  I had made the tool shown below on the left from some plumbing parts which worked fine if the case was annealed.  I just finished a new variation on my crude but affective de-capping tool that will flare and de-cap all at the same time.  The flared section is adjustable.  Should do the job in one operation.

Jack 

JLouis wrote on Jan 23^rd, 2015 at 9:14pm:


JLouis,

Could you elaborate on this a bit?  I'm seating the bullets so that the throat just shows on the front of the base band.  I thought I would try seating them a little deeper tomorrow.  Does case length have an effect?

Thanks,

JS

  The cause of this is the same sort of pressure wave that causes chamber ringing.   The high pressure wave reflects off the base of the bullet and on its way back, high pressure gas gets between the case mouth and the chamber.
   It can best be prevented by not constraining the powder charge into a symmetrical mass.   If you restrain the powder with a wad, leave it a little ahead of the powder charge and there will generally be no problem.
    The reason that lightly expanding the case mouth works is that it prevents the reflected pressure wave from forcing gas between the case mouth and the chamber.  Doesn't take much, just slightly bell the mouth so that it drags when chambering the round.  This usually has to be done for each shot.

CHRIS
RGChristensen

Years ago I had a 38-55 that would pucker case mouths every shot. I made up a tool to bell the case mouth and it worked. As I was reloading at a match Charlie Dell asked why I was belling the case mouth. I told him and he suggested that I put a wad at the mouth and turn the case so the powder was oriented to the mouth of the case then put it in the rifle and fire. He told me I would probably have to up my charge a little to get back to the proper velocity. I tried it and it worked no more puckered case mouths. When I got home I ran the loads over the chronograph and had to up my charge 2 10ths of a grain to get back to the right velocity with 4227. 
  It is useful to note that Charley when doing his testing on chamber ringing and after ALWAYS seated the wad .050” off the powder then tipped the case down and then put the case in the chamber. He was a bear about this one thing and would ask over and over if we tipped the case to the front before loading.

40 Rod

I had the same problems with .38-55 cases of various makes. Problem was solved when I changed the powder
to AA No. 9 after I had tried annealing, belling out case mouth with no success.
Pete