jl7030--Welcome
First off the 45/410 was never designed to be a 100 yard gun , granted it may shoot 100 yards but how accuratly is anyones guess .
As for your gunsmith telling you that if it fits , then it should shoot is just plain dangerous .
Tim is right about standard 45 lc handgun ammo not being up to snuff , your best bet would be to get a 44 mag or 45/70 handi with a sb2 frame .
Richard