Sportered 1917

[Calfed]

Thanks for your insight, Patrick

So the GP-11 "is most certainly NOT 0.308"; you've measured it at .3079. Is that a difference of .0001? I won't quibble with you about that .0001 difference in our measurements, since it is with-in the tolerance used by Sierra in the manufacture of their bullets.

I measured it at .308, although it was at the widest point and I was not able to measure the distance along the projectile that maintained that diameter. If, you want to call the point at which the bullet mic's .308...I mean .3079.. a "driving band" and not the bearing surface, that's OK with me.

CarteachO, a poster on a number of mil surp forums and a prolific analyzer of things milsurp, did an analysis of the GP11 and found the diameter of the projectiles to range between .3076 and .308, so I guess both our measurements are with-in the range that he found.

Carteach0: 7.5x55 Swiss GP-11, weighed in the balance

Your specs of the bore/land difference are interesting. If correct, they confirm what I wondered about Swiss barrels--that is: are the lands "taller" (or the grooves "deeper") than US .30 caliber barrels. Your figures show a bore/land difference of .0103, for a groove depth of .00515. That is some what less than figures that I found subsequent to my last post, but still considerably more than the US spec groove depth of .004.

That seems to indicate that , as you posted, the Swiss barrel would take a lot of firing before the grooves were worn beyond the US barrel specs.

Thanks again,

Steve