Howdy Rick,

Just a curiosity question:  have you tried any other bullets?  While many have great success with spitzer style bullets such as those A-Max... most find that a round nosed bullet works well.  Krags were originally designed to fire 220 gr RN FMJ bullets at around 2000 fps.  Criterion barrels are manufactured to exact standards of the original design, so it might do well with the RN.  I have a friend who exhibits "Tack-Driver" accuracy shooting 150 gr RN Hornady bullets.  I fire the Hornady 220 myself.

Otherwise, I would check the tightness of the bands, and trigger guard screws as others have stated.  What ever the problem is, the fix might wind up being simpler than anyone imagines. 

Great to hear that your sporter is a joy to shoot!  Krags will do that to a person!!!

Happy Shooting!