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Somewhere in my materials I have a short note in American Rifleman from the '50's identifying Finnish State Rifle Factory experiments with bore wear.

Included is an interesting graph of tracked accuracy over the course of the experiments with 7.62x53R ammunition.

Summary is this; As long as bullets were sized to GROOVE depth, the amount of BORE/LAND wear was relatively irrelevant AND ACCURACY STANDARDS WERE THUS MAINTAINED TO 35,000, YES, THIRTY-FIVE THOUSAND ROUNDS SHOT THRU THE GUNS.

The key here was that accuracy fell off due to bore/land wear in conjunction with increasing groove depth due to surface erosion. Since there was less and less "land" to grab the bullet, and more and more "looseness" around the bullet due to erosion of the bottom of the grooves, the bullet needed to "grow", and if it did, thru the use of bigger bullets, accuracy was just fine. This is NOT the same thing as shooting undersize bullets in a barrel possessing proper bore diameter with excessive groove diameter. Such barrels often shoot very well indeed, at least as long as they are relatively new.

The accuracy standard of the time was 3-shots into 3cm at 100 meters IIRC.

If somebody calls me a liar I'll be forced to go mining for the information to prove what I am saying here. I may have to quit my job and stock up on rations for the extended stay in the basement rooting thru old moldy AR magazines, and it might take me some months but I can probably locate it.

Daryl and I can both vouch for the accuracy of oversize barrels with undersize bullets in our 9.3x57's. But our barrels have in-spec bores {land diameter} tho having obese groove depths. As long as those lands hold up we'll do just fine. If they wear, I suspect accuracy will then fall off precipitously. Of course, both of us have sizing dies which we can use to custom fit bullets which we do now as a matter of fact. This merely being identical work to what the Finns accomplished and proved in the State Rifle Factory experiments.

That is why I wondered about Ruger's dimensions. If they are spinning out .303/.315 barrels all should be fine with .311 bullets for quite a bit of shooting.

But if they have , let's say, .306 or more land diameters with .315 grooves, things might be henky right off the bat. In such a case you have less grab on the bullet shank and none around it. Mere groove depth not being the problem.

I'd sure like to see what fellows are getting for land diameter of slugged Ruger No.1 barrels.

Also, IIRC, Ruger rifling form is narrow lands, wide grooves, yes? Check the rifling form. This type is likely least able to handle oversize LAND diameter as there is just not much metal there to engrave the bullet.

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Edited by 9.3x57 (18/08/11 09:58 AM)

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