Loading .452 saboted bullets in my Omega is fairly difficult (not like you're describing though).

.451 bullets load considerabley easier; on par with a patched .490 round ball in a GPR.

Power Belts easily slide down the barrel.

I suggest trying some .451 bullets, if that doesn't work try some .429 caliber bullets. The .429 bullets use the green sabot.

I get good accuracy and performance from the 260 grain .451 Nosler Partition HG bullets, they're pricey though.