Like the title says, why don’t more manufacturers offer 1:7 rifling twist with their AR clones? Maybe that’s a stupid question but, I can’t figure out why.
Joe Mamma
Because companies believe that most consumers want 1/9 twist instead of 1/7.
You have to remember that a very small group of AR shooters want a 1/7 twist barrel. In fact I think most of the worlds 1/7 twist fans live on this forum. 
C4
I will do you one better why not offer 1/8 twist?
Most view this as a Varminter twist rate (for whatever reason). BCM is working on some SS barrels in 1/8 twist.
C4
Most guys I see with 1:8" barrels are competition shooters. My service rifle comp barrel is a Krieger 1:8" and I wish my carbines had the same twist rate.
Might be a dumb question but why is 1/8 more desirable twist rate than 1/7.
I’m thinking of adding spare barrel to my SPR and the barrel I’m looking at is 1/8.
My current barrel is 1/7, both barrels are stainless.
I shoot SMK 77 grain reloads.
Thanks
Paul
It was always my understanding that 1/7 was to allow for the longer tracer rounds. I thought that 1/8 was good for pretty much anything other than the tracers and the lightest rounds.
The 1:7 twist is a good question. Twist rate is certainly debatable in most company. I have only 1:7 but many people swear by the 1:8 and even 1:9. To each his own I guess.
The question that really gets me though is why some AR manufacturers refuse to correctly stake their carriers with a Moacks or other homegrown device of their liking when it has been repeatably shown that this is a huge weak link in the AR platform if not done correctly. I guess we will never know that one!
That is correct.
I have launched many 80 grain Berger VLD bullets into the 10 ring at 600 yards using both 1/8 and 1/7 barrels. Twist made no difference, bullets made nice round holes in the target regardless of which barrel I used.
Out of an AR?
I’d imagine so. I use the same bullets in my competition AR.
The vast majority of rounds fired out of AR’s by civilians will be 55gr ammo.
1:9" twist is perfectly suited for this.
1:9" twist will reliably shoot bullets up to 69gr with some 1:9’s also working for 75gr bullets.
This is partly a matter of twist rate tolerances and also of barrel length.
A 24" 1:9" barrel is MUCH more likely to stabilize 75’s than a 16" 1:9 barrel.
Twist rate tolerance is not something you hear about very often.
Believe it or not, the twist rate tolerance on most “production grade” barrels is +/- 1/2".
This is important.
You can have a 1:9" twist barrel that’s actually a 1:8.5" barrel, or a 1:9.5" barrel and it would be “in spec”.
That’s why SOME 1:9’s will stabilize 75gr bullets…
Now, the 1:8" twist should get you through the 77’s and maybe the 80’s
Optimum twist rate for the 80’s is 1:7.7 and that’s why Krieger offers that specific twist.
1:7" twist is only needed for the long tracers.
How many civilians on this board make a habit of shooting M856 tracers that would actually REQUIRE the 1:7" twist?
I’ll bet the number is small.
If you kept yourself to 69gr matchkings and 62gr M855 ball, the 1:9" twist would cover you nicely.
Points well taken Randall, but some people have to make use of or want the ability to use 75-77gr projectiles, given their superior performance on malevolant squishy reactive targets.
Would a 1x8 twist barrel, say in stainless steel, wear more slowly than the same barrel in 1x7?
Thanks!
This is ONE of the problems inherent with purchasing Bushmasters for duty use. Weight and the twist ratio makes the Colt 6721 a poor choice also. Anyone want to guess which rifles I bought:rolleyes: ?
It becomes even more of an issue when you want to go the SBR/suppressed route and have some chance at decent terminal performance and shoot the 75 gr. TAP stuff.
Barrels “wear out” due to flame cutting and cracking of the throat area. The throat, by its definition, is devoid of rifling so the rifling rate is irrelevant to a barrel’s longevity.
Not maybe the 80s. Definitely the 80s. Too many target shooters happily shooting 80s out of 1x8 to be a “maybe” or a coincidence.
Yes, out of a Rock River National Match AR15.
1:8" twist would be the best choice for 75-77gr bullets.
Unfortunately, most chrome lined chromoly barrels come in either 1:9 or 1:7 and 1:7 becomes the obvious choice given the two twists to choose from and ignoring the stainless steel 1:8 options.
Barrel length is an issue here.
In 20" barrels, no problem.
In 10.5" barrels, the 80’s are right on the edge.
The 77’s should be fine in 10.5" 1:8’s though.
It’s because that what the military uses. The military used the 1x7 in the M249 because its stabilized the very long M856 tracer projectile very well (the M856 projectile is a tiny bit longer than a 80gr Sierra BTHP, it’s a bullet length issue to stabilze the M856 not so much the weight, I forget what a M856 projectile weighs but if I recall it’s lighter than 80gr).
When they started developing of the M16A2 they needed something to stabilize the SS109 projectile and they just used the 1x7 since they knew it already worked so well with the M856 (so as to not reinvent the wheel) and then the rest of the series used it as well…M16A3 & A4. The M4 and M4A1 also use the 1x7 (same reason, it worked why change it?).
The 1x8 will stabilize a 77gr round out of a 18", 20" and 24" barrels. (I’ve not shot 1x8 with barrels shorter than 18")
1x8 is pretty desirable by many (me included) and it seems more and more barrel makers are starting to offer it.
The 1x9 will stabilize a 77gr out of 24" barrel simply because it has a lot of velocity. A 10.5" 1x9 won’t stabilize it because of the lack of velocity.
1x9 will stabilize what ‘most’ people shoot. Most people are going to shoot 50-69gr rounds simply because it’s much cheaper than 73-77gr. Those that want the option of shooting 77gr should buy 1x7 or 1x8.
True. I was referring to 20" barrels and longer.
rotation rate = linear velocity X rifling rate
the reason the 1/7 is not as popular is a subject that will have many answers and the debate would be endless. what I can tell you is the 1/7 in a 14.5 and 16 inch barrel with 75 and 77 grain ammo is all the reason I need ,because it works superbly. anyone who has shot 77 grain SMK out of a 1/7 knows just what the results are and needs no further explination,it flat out works.