darthvaj,

I believe the pipe you show is like the one in the pics I have attached. That being the case, I think the pipe was originally intended for the Rossi 60. The second pic shows it beside a Byron #5 pipe for the OS 91...... notice the difference in size comparison in the expansion chamber between the two. The correct pipe for the Rossi 91 would be very similar to the #5 pipe, if not the same. I think the one for the Rossi 105 was even larger.

I wouldn't go searching for another pipe either, just follow the lead of what the other's have said. You will be happier in the long run.