Question about rifling

B

budd

New member
Guys,
I know what rifling does and its nessecity. But, from what I have read on thes forum and others forums I am confused what is 5-R rifling and how it differs from the ballard style rifling and polygonal rifling, and is there any differences and/or advantages or dis-avantages 5-R rifling may pose? And why is it refered to as a "progressive rifling"?

Can anyone enlighten me??

V/R
J Budd
 
Per Thompson Center

5R RIFLING™
5R rifling’s unique design provides benefits to the shooter by causing less bullet deformation. How? By design, the edges of each land do not cut into and deform the bullet jacket. When the bullet jacket is less deformed, there will be less jacket fouling in the grooves. The results are better consistency of accuracy from shot to shot, greater bullet stability over multiple shots, and ultimately a rifle that’s easier to clean thoroughly. Standard on all Bolt-Action models including TC's Icon and Venture.
Click to expand...
 
It's also called 'gain twist' rifling. The initial cut is something like 1-12, then gradually tightens up to 1-8 toward the muzzle. At least this is true with my M&P Sport.

The lands are bevel cut at about 60 degree angles, instead of the usual 90 degree. It's more of a polygonal design.

I haven't heard of anything negative. It's actually considered a better design from what I gather.
 
I've heard nothing of "gain twist" in the R5 rifling. Some rifles use gain twist rifling, most do not, but I think that would be a seprate thing. Remington shows a 11.25 twist with no mention of gain twist. Basically the corners of the 5 lands have a radius cut on them. That is where the "R-5" comes from. It is supposd to improve accuracy.
 
5R rifling, as I remember, originated in Europe. It may have been first used in the USA by Barrett (Boots) Obermeyer making 7mm match barrels for the 7mm Rem. Mag. cartridge. Sierra Bullets had just introduced their 7mm 168-gr. HP Match King bullet and a good friend set the 1000 yard scope sight match record at the Nationals with it in 1970. So many folks changed their 30 caliber magnum barrels for a 7mm one. But Sierra's jacket material was such that traditional rifling weakened it and they often split apart in mid flight. Boots Obermeyer started using this rifling whose edge shape doesn't move as much jacket material around engraving the bullet and the Sierra's did well thereafter. Too bad those bullets weren't consistantly accurate until the late 1980's.

5R rifled barrels shoot just as accurate as conventional rifling does. Any rifling style that minimally distorts bullets and doesn't change pitch for the length of it is great. Greatest cause of poor accuracy in an otherwise perfect barrel with exact bore and groove dimensions is the twist isn't constant from throat to muzzle. If it changes, that further distorts the bullet jacket and that opens the door for unbalanced bullets. And unbalanced bullets don't shoot accurately.
 
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5R stands for 5 groove, Russian pattern.
Mr Obermeyer supposedly designed it based on examination of an AK74 sent back from Afghanistan by a Soldier of Fortune magazine contributor. That in the day when we thought we could support Afghanistan to make Russia look bad and have the Afghans like us for it. Riight.

Anyhow, according to the article in American Rifleman, they got this souvenir AK74 and a very small supply of ammunition to wring it out with. The AK barrel is rifled with four grooves in what the British used to call "trough shaped" rifling, with the grooves tapering in width. They got Obermeyer to measure the AK74 barrel and make up a PV (Pressure and Velocity) test barrel for the first 5.45x39 ammunition seen in the western world.
Supposedly he like the concept but went to five grooves for whatever advantage the odd number school of thought finds in a land opposite a groove around the bore.

If a barrel is designated 5R, it came from Boots Obermeyer or Mike Rock, who got his start working for Mr Obermeyer. Other brands offer similar rifling profiles but call it "canted rifling" because they can't use the Obermeyer trademark.
 
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