ORIGINAL: retrieverman
I don't know what a QLA system is so I guess I don't have one, but I do know for a fact that the 54 cal 60 gr pelletsfit easily down the barrel of my Knight Disc rifle as well as my Ultimate. I have never tried them in my Encores or Disc Elite.
I'm not sure about Knights, but Thompson Center offers the flared-open muzzle (QLA) that allows easy starting of your bullets. I know of no other way anyone can load 54-pellets into a 50-cal rifle ... without damaging the shape of the pellet.
Any pellet damage can increase - then create dangerousbore pressures by placing air gaps between the plug and bullet.
The only other exception is Hodgdon Inc. improperly loading 50-cal pellets in that 54-cal box. Yes.... Hodgdon does strange things sometimes. One time, my jug of 777 was filled approximently with 50% Pyrodex and 50% 777. Both are/were bottled/packaged in the same building.