02-08-2012, 09:15 PM
elkbow Wrote:And there is a reason why other manufacturers are using the 7.62x39 bolt, it has less recess, allowing for greater pressures than the Grendel's 50,000 psi limit...
This is some what incorrect, but not the first time I have seen such internet wisdom repeated. The change of 0.011" of depth of the bolt recess (3 sheets of writing paper) has significantly less bearing upon the life of the bolt than surface finish, let alone the geometry. What it will adversely effect is the extractor strength. The Grendel bolt design is not a simple opening up of the 5.56 bolt as typified by what is now referred to as the 7.62x39 bolt. The bolt is a balance of the extractor and the bolt geometry with the steel type used and the heat treatment. The pressure limit was set to 50,000 psi to provide a wide margin of error and also allow for an exceptional cyclic life. It also balances the recoil generated with weapon controllability in a platform weight conducive to the small platform the cartridge was intended to fit.
There have been a number of variations on chamber supposed to "improve" the Grendel. Most notable is the LBC which is particularly amusing as it was a design tested in prototyping and then dumped, that the reamer maker just regurgitated. The typical improvement may prove fruitful for the individual but it may also create frustration. Loading data may or may not be applicable. The Grendel chamber proper was set up to allow it to be easy to achieve good accuracy in bulk production with only a little attention to the details. It is tolerant to both long ogive target bullets, short flat base varmint loads and long but blunter hunting loadings. The typical set up with a half decent barrel will usually outshoot its owner.
As to case life this seems to be another internet rumor. Unless the shooter uses an appropriate bushing type die set, 0.005" on diameter or 0.003" will have no effect at all. The sizing die will move the brass way beyond this both below and then back up as the sizing button passes. What the "tight" neck does without adequate insight is to relocate the origin for the shoulder/neck radius to a possible bind condition as the various manufacturers produce differing batches.