No.4 bolt heads specifications

[bow]

Do you mean 0.639" ?

0.639" Alan... i did a mnistake on writing.

---------- Post added at 07:56 PM ---------- Previous post was at 07:53 PM ----------

If you use small rubber/neoprene o-rings at the base of the cartridge for the first firing your brass will never know what the headspace measured. It'll last just as long or longer than can be achieved by any other method

But ith o-ring will reduce headspace first time the brass is shot..but the second time , withouth o-ring , it will be stretched ... What i hadn't understood?