Is this an Old Model Vaquero cylinder? We had that problem with the OMV's in .44-40 originally, but I wasn't aware of it in the .44 Mangle-em's. Are you intending to shoot jacketed bullets? In that case, you should have the throats reamed out to groove diameter of the barrel. With my .44-40 OMV's and the .425" throats, I have just been shoting .429-.430" hard cast bullets ONLY (BHN 12-17). I get great accuracy and virtually no leading. The way that works, is the bullet compress going through the throats, but the compressive strength of the alloy is such and the dwell time in the throats is such that the bullets re-expand in the forcing cone.