After doing some research, I think a 1-3/8" round nose bit will work on the HW80S stock. 1-3/8" = 1.375".1.375" = roughly 34.925mm, which is just larger than the receiver tube. The receiver in-letting can also be made larger using a 1-3/8" dowel/sand paper.Now I just need the bit size for the Rekord trigger and cocking slots .I will measure a HW95 receiver tube and do the same ....