I am not sure why you would not think the patch would "seal the bore like a sabot would". IMO the patch will seal just fine. BP cartridge shooters have been shooting paper patched bullets for a long time, with great long distance success. It sounds like you have bullet to patch to bore fit just right. You should have great success. But just like anything else in shooting, each individual rifle is hit or miss.

It has always been my opinion thata sabot is only a "convenient"patch. Tom.