Ganegrei
Comblock Convert
Also, if you are talking about a Mosin, Wally World sells a 3-pack of flexible (rubber-like) silicone funnels for a few bucks. Pull out the bolt and one of them is just the right size to fit down into the chamber. Just pouring hot water, or hot water with some ammonia in it, down the barrel before normal cleaning will do the trick. The corrosive compound in the primer produces a kind of salt that ammonia neutralizes, and that hot water will flush away. You can do this over the drain in a bathtub or into a toilet if you haven't got much room.
Brilliant!