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cornstalker
Reply with quote  #1 
It's just a matter of time before I shoot the barrel out of my 6mm284. I am looking ahead to replacement and am thinking about buying a Pac-Nor. They list 3,4,5,& 6 groove barrels, as well as polygonal.

Can someone explain the benefits/drawbacks of the various groove options to me?
Bob3700
Reply with quote  #2 
I don't think the number of grooves means a thing for accuracy. A smaller number of grooves may provide a wider surface that will have more material to wear.

Personally, I have had both button and cut rifle bbls. Both shoot equally well. Cut bbls seem to last longer, especially when high volume , high speed cartridges are used Bob fv
spclark
Reply with quote  #3 
Some folks advocate odd-numbered land-and-groove count so as to make for a better-balanced bullet at speed, the theory being that even-numbered counts tend to maximize the distorting forces on a bullet by putting lands/grooves opposite one another. Uneven counts put a land opposite a groove.

Cut vs. buttoned is a subject for another debate entirely.

Polygonal rifling or 5R / 5C land contours (depending on who's brand you're considering for a 5-groove) is supposed to decrease the amount of distortion bullet jackets undergo by making the transition between lands and grooves less aggressive.

The 5R/C type seem to copper-foul a bit less too, as well as being somewhat easier to clean when carbon gets burned into the tight areas where the bore surface changes direction.

Polygonal bores are said to shoot faster than bores of similar diameter in conventional rifling profiles but may foul faster too.
butchlambert
Reply with quote  #4 
I don't think anybody has proven anything about any advantage of amount of grooves, shape of lands, and longevity. A lot has been written, but nothing proven.
Butch
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