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