Re: marlin/glenfield old model 60
The new buffer works just fine even though the retainer pin hole is larger in the new style block. The hole was made larger to help alleviate the cracking problem.
The pin is just there to hold the buffer in place when the rifle is disassembled. When it's assembled, the buffer rests up against the back of the receiver. when the bolt travels back and hits the buffer, it gets sandwiched between the two parts. The hole in the top of the buffer is part of the "suspension" system so to speak...when it's being compressed, that's part of what allows the block to flex ever so slightly.