removing a burr in the barrel transfer port.

TP ~ transfer port. Anyway, I've had to use a bench grinder or a 4 1/2" angle grinder to shape or decrease the size of the rubberized conical tool and the felt tip one. You may have to remove the barrel to efficiently get to the burr. You must use finesse in doing something like this. The first bit listed will take material off quick! The second is much less aggressive. The third is for finishing/polishing.
If you're not confident that you can take your time and do it right, don't. I'm just tying to help in suggesting what has worked for me.