Advantages of a 1/8 5R barrel?

[Jim Watson]

Harry Pope thought so.

Bartlein will let you make up your own mind in modern calibers.

S&W/TC factory gain twist barrels? Where does S&W or TC say so?

Brian, I think they gave up on the bismuth, the current M855A1 bullet is just steel and gilding metal.

 

[9x19]

The 1/8 being gain-twist is news to me as well... I'll have to ask to pull the bolt and look next time I'm at the LGS.

At my level of skill, and from an AR, I doubt I'd notice any accuracy improvement from the gain-twist style of rifling.

 

[Jim Watson]

I don't know if anybody would.
Harry Pope liked it but Schalk, Schoyen, and Petersen didn't, and they were no slouches at making lead bullet rifles.

The company that started out as the modern Gain Twist Rifle Barrel Co. was not even making gain twist barrels when they were bought out.

There is a guy in Canada making nice ones for the old calibers and, as I said, Bartlein will give you any twist any gain you want.

 

[Jimro]

That article in American Rifleman was by Maj (ret) John Plaster, where he states that the 1/7 twist will give roughly twice the size of groups as a 1/9 twist. But you have to dig for the actual numbers, which are 1.6 moa and 0.9 moa with M855A1. I really didn't care for the article as it was a lot of hype and not a lot of analysis, specifically I can point you to DTIC reports where increased terminal ballistics were considered as part of the Army's "Green Bullet" program as far back as 2005 when a Canadian projectile was considered.

Considering the accuracy standard for M855A1 is the same as M855, which is roughly 4 MOA from an M4 rifle, I'd say that arguing over twist rate is really picking hairs.

When you shoot MM855A1 through a 1/8 twist barrel, as the AMU did, it performs accuracy wise quite similar to match grade ammo, at least in the lots that were tested.

Jimro

 

[Hammercrg29]

Barrels with 1/8 5R rifling

Hi guys, I have a gen 1 S&W M&P15 sport with a 1/8 twist ratio with 5R rifling and melonite finish that I have spent a fair amount of money on for upgrades but it's what I wanted to do. I put a free float hanguard on and I also dropped in a flat faced Geiselle super dynamic enhanced trigger. I wanted to test out the accuracy limits of it but don't own a high end optic so I borrowed a Leupold Mark 4 ER/T from a shooting buddy who is really into long range/precision shooting. I don't care what anyone says (excluding military/LE snipers/professional shooters/competition shooters), that 1/8 twist and 5R rifling is great and performs best with heavier rounds (between 69 and 75 grain). I can't shoot sub MOA groups at 200 yards with this setup, I don't have a spot where I can test out longer than 200 yards at this time. I would dare say that if I were to experiment with hand loads I could have accuracy results just as well at longer distances (maybe out to 500 yards, not much further) with this setup. I have spent a fair amount on different accessories but simply don't have the money to drop on a high end scope. Some day I will but it won't go on an AR it will end up on a custom tac driver project. But this is my own opinion and I honestly believe that the gen1 M&P Sport barrel setup is better than the new Sport II. I could care less about a dust cover or forward assist.

 

[rickyrick]

There are and have been instances that I don't want faster twists than 1:9, but the popularity of 1:8 and 1:7 twists makes them economically appealing to a regular guy like me. Sure, I mainly shoot 55gr and varmint bullets at varmints, rarely have I purchased anything heavier than 69gr. 1:9 - 1:12 twist would probably work great for me, but the market is saturated with 1:7 and 1:8, so they're workable for me.

Funny story, in the midst of one of the AR panics, hardly an AR could be found.
I was browsing a sporting goods store and there was one gleaming AR carbine on the rack. A customer giddy with excitement got the clerk to let him see it. I could tell that he really wanted to get it. It was priced as it should have been with no panic gouging price.
The moment he discovered that it was a 1:9 twist and not 1:7 he handed back like the clerk insulted his grandma and walked out.

Most average joes shooting 55gr fodder, wouldn't notice the difference I think.