Question on 7.62mm x 51mm vs .303 BRit

[Thunderbox]

The no4 is a weak, stretchy action when you start to load it hot,

Really? I'd say that was merely much-repeated myth that simply isn't supported by any evidence.

7.62mm/.308W No4 rifles have been around for decades, and there is no data around to suggest they are in any way inadequate. I had one Envoy accompanied by a log book showing over 9,000 rounds of 155gn match ammo - that one was still tight on a "0" bolt head - and another where the owner had really been stoking it with 168 and 190gn bullets for 1000 yds - ditto on the bolt head.