| DarylS |
| (.700 member) |
| 22/07/12 01:41 AM |
|
Re: 1903 groove diameter
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Quote:
Could there be a difference in the design of the MS rifling that upsets .263" bullets into the larger groove diameter to give obturation?
I've long thought there was something strange and deep-looking about the 1903's rifling, beyond the fast pitch. And no wonder - with a bore of .256, a groove of .268 would be about 50% deeper than used in most American rifles/calibres. Maybe something has to give.
.006" per side in older rifles is common for some Euro rifles. My 9.3x57 has .0065" rifling per side. It has a .370" groove diameter instead of .366", coupled with it's .357" bore, giving .013" difference instead of modern idea of .008" difference.
The reason I mention this, is that it shoots .365" and .366" jacketed bullets sub 1" at 100 meters. Yes, the blowby, whatever is there, is not good for the grooves, but it isn't a varmint rifle that goes through thousands of rounds a year. It will last me until I die and so will that 6.5 last you, shooting .264's IF they are accurate. If the rifle's chamber will allow the larger bullet to be seated in the case neck, then use the .268's. If not, use .264's. There's only .002" per side difference.
Some time ago, I bought picked up some bulk 6.5's that had huge lead round noses and measured .262". I gave them to a friend with a .266" 6.5x55 M38 to try - they shot quite well in it too, - enough to harvest a moose.