5R rifling works best with light or heavy bullets?


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Skribs
December 30, 2011, 01:36 PM
If you've followed another thread I made recently, I'm looking at getting a S&W M&P15 Sport soon, and it uses the 5R rifling. Would lighter or heavier bullets work better out of this scheme?

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helotaxi
December 30, 2011, 01:39 PM
The rate of twist, not the type of rifling, determines the highest weight bullet you can shoot but even that doesn't determine what shoots best. You can't determine what bullet will shoot best until you've tried them.

Skribs
December 30, 2011, 01:45 PM
I thought I read somewhere that 5R changes from long to short twists as you go down the barrel, which is why I mentioned it.

snakeman
December 30, 2011, 02:42 PM
5r rifling is a type of rifling that has 5 lands and 5 grooves A land opposes a groove instead of a groove opposing a groove. It was designed to reduce bullet deformation and barrel wear. It cuts a round groove through the bullet instead of a square one to reduce resistance. This type of rifling is claimed to be more accurate. As far as light or heavy bullets goes that depends on your particular barrel and twist rate.

Jim Watson
December 30, 2011, 02:43 PM
Nope. 5R means 5 groove Russian pattern. It is the old "trough shaped" rifling of the late 19th century brought back for the AK74 (with 4 grooves) and commercialized in the USA by Boots Obermeyer and now others. Broughton and some others call it "canted" rifling.

It is supposed to engrave the bullet more smoothly, wear longer, etc., etc.
I think it has more to do with the quality of manufacture than the shape of the grooves.
The twist rate determines the length of bullet that will be stabilized.

Bartlein T Style is the main gain twist rifling that I know of. They will make any twist and any gain factor you care to order. I don't see where they say what profile land and groove they make, though.

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