I run all my 77s and 97s with a 3.2mm TP

I have a special "Gold" drill bit just for that job.

3.6mm is still perfectly fine but if it's over 4.0mm then it's sleeve-down time.

JB swore by 4mm so it seems the TP diameter is variable but different sizes will obviously affect the shot cycle considerably.

I like 3.2mm myself

Matty