I have 3 CVA/BPI guns with their eazy load muzzle/QLA system. All 3 shoot sabot's, conicals and even PRB well. Under the right conditions they will hold around 4" groups with heavy conicals at 200 yards, around 3" with sabots at the same distance. I would guess that the centering of the recessed muzzle and possibly the diameter of the cut back may be the key to whether it works well or not. I find that it is easier to get a load started straight in the bore with the QLA since it does not allow much side to side wobble which can damage the base of the bullet and could affect the accuracy.

Another technique you could look into is to have the GM muzzle coned. I saw a 40 cal FL that had this done and you could start a RB with finger pressure. The muzzle looked about the size of a 54 cal but sloped in to 40 within about 3/16". I'm not sure how that would work with a conical though.