natedog
Member
I was told on this board that HK's polygonal rifling, in this case on the XM-8, increases velocity out of a 12" barrel to 20" standards. True?
Polygonal rifling and velocity
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Destructo6
Member
I read that, too, but I wonder. Polygonal rifling is suppossed to allow a better gas seal, but I don't know if it makes that big of a difference. Durability is usually one of the selling points.
Andrew Wyatt
Member
I suppose I should have put a smilie on that post.
One of the often touted advantages of polygonal bores is that they increase velocity. it's usually around 20-30 fps, though.
One of the often touted advantages of polygonal bores is that they increase velocity. it's usually around 20-30 fps, though.
I'm not sure on polygonal bores.
I could see one nice advantage, ease of cleaning, no sharp corners to grab ahold of jacket material and hold onto it ofcourse that's provided the polygonal bore is of a nice surface finish. Would be nice to have something that cleans even easier than a well built hand lapped match grade barrel.
As for the increases in velocity, I don't have a clue, if they reduce friction in the bore I could see where perhaps velocity could actually drop due to reduced chamber pressure.
But a 16 inch polygonal barrel producing the velocity of a 20inch normally rifled barrel while using the same ammo, doesn't quite follow.
I could see one nice advantage, ease of cleaning, no sharp corners to grab ahold of jacket material and hold onto it ofcourse that's provided the polygonal bore is of a nice surface finish. Would be nice to have something that cleans even easier than a well built hand lapped match grade barrel.
As for the increases in velocity, I don't have a clue, if they reduce friction in the bore I could see where perhaps velocity could actually drop due to reduced chamber pressure.
But a 16 inch polygonal barrel producing the velocity of a 20inch normally rifled barrel while using the same ammo, doesn't quite follow.
FireInTheHole
Member
Well poly barrels actually increase surface area correct? I can see how this could be ofset by a better gas seal.... but I'd love to see some data on this.
Anybody know how bullets hold up in poly barrels @ 3000+fps?
Anybody know how bullets hold up in poly barrels @ 3000+fps?
pretty sure that a rifled barrel would have more surface area in contact with the bullet, the raised rifling has it's sides that contact the bullet as well. Both polygonal and conventional rifling should make full contact with the bullet and provide excellent seals, difference being in how the bullet is deformed.
Marko Kloos
Moderator Emeritus
If polygonal rifling added an effective 4" of length to any given barrel, don't you think we'd see nothing but polygonal bores out there?
Destructo6
Member
Polygonal barrels are usually hammer forged over a mandrel. The cost may be a factor in their relative rarity.
Badger Arms
Member
The H&K company line years ago was an 8-10% gain in velocity with their HK-91 rifles. That's fairly substantial. IIRC, the SL8's I've seen had standard rifling, though, and not the polygonal.
Even 6% velocity increase means a 2700 fps initial velocity ends up being 2850 or so. Fuzzy math, but you get the idea. That's significant enough for me. Hammer forged barrels are cheaper to make in quantity, more expensive to make in small batches. They also tend to be a tad less accurate. The major reason for their limited adoption is the huge investment required to tool up for production. My opinion.
Even 6% velocity increase means a 2700 fps initial velocity ends up being 2850 or so. Fuzzy math, but you get the idea. That's significant enough for me. Hammer forged barrels are cheaper to make in quantity, more expensive to make in small batches. They also tend to be a tad less accurate. The major reason for their limited adoption is the huge investment required to tool up for production. My opinion.
CMcDermott
Member
Lothar-Walther, Winchester and Ruger have all gone to hammer-forged barrels, and they are standard rifling, not polygonal.
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