TraderRik Wrote:I have a new PSA 20" stainless upper that I bought a month ago. If I am measuring the bolt correctly, and if my el cheapo Neiko digital caliper is accurate... the bolt measures 2.7958, and the firing pin measures 3.2645.
Soooo, what does this tell us?
You should be gtg. Your PSA Bolt is basically 2.80 and your firing pin is less than 3.270 so you should be ok. Your firing pin is roughly .01 shorter than a milspec firing pin. If you have to replace your firing pin just ensure to buy a shorter firing pin from PSA to match your PSA 6.5 Grendel bolt or buy a milspec stainless steel firing pin and reduce the length .01.
Brownell’s sell a firing pin protrusion gauge. Minimum firing pin protrusion is .028 maximum .036.
https://www.brownells.com/gunsmith-tools...26477.aspx
My milspec firing pins measure 3.279. Normal tolerance can vary the exact length which is referred to as tolerance stacking when two parts together don’t fit/work. Both parts being at the extreme of manufactured tolerance making parts either to long or to short.