454 Casull Question

A friend of mine has a .454 Casull that he has only shot a few times because it was such an unpleasant experience using factory ammo. I had read articles in TFS by Paco Kelly and Jim Lewis describing their favorable results with cast bullets in the .454 and we loaded up some commercially cast  hardcast 0.452 bullets that gave poor results.  The Ruger has 0.454 throats and groove diameter, and due to limited shooting time we switched to jacked bullets to see if we could come up with a midrange load (around 1200fps) he could use for the upcomig deer season.  Using midrange cast bullet loads suggested by Paco and Jim we loaded up some 250 grain JBs and had favorable results, but on 2 occassions stuck a bullet in the barrel (a new and unpleasant experience for me).  The stuck bullets occured with 2 different powders (W296 & H110) and 2 different primers (CCI 400 & WSR).  Loads were given a heavy crimp.  In both instances there was a pop when the primer detonated and the bullet lodged around 2 inches down the barrel.  When the bullet was removed it pushed out a hard wad of sorched powder.  I would think that if the primer had enough energy to push a JB down the barrel, it would be powerful enough to ignite the powder charge.  Is this a unique case where occasionally the small rifle primer has too much energy and creates a condition where the powder ends up acting like a filler as is pushed down the barrel along with the bullet?  Somewhere I have read that in some situations hotter (magnum) primers are not compatible with certain powders.  I have also considered the possibility that for some reason the stuck bullet  occured because that round did not receive a full crimp, the bullet moved forward prematurely and the pressure in the case was not high enough for efficient powder burn. So, as you can see, I am at a loss as to why we get the occasional stuck bullet and any suggestions will be greatly appreciated.