Beginning to reconsider 1:7 twist for myself

[Mark21]

Over the past couple years I've upgraded most of my rifles to 1:7 twist rate because it was better at stabilizing the heavier rounds that I shoot occasionally.

But a (non-mil, non-contractor) friend recently asked what was best for him for an all-around AR. I thought about what I shoot: 55gr surplus, 55gr Prvi, 55gr S&B, 55gr LC, and so forth. I do have some 75gr TAP (maybe 300 rounds) for self defense, and I reload 77gr Matchkings once in a while for competitions, but out of the thousands of rounds I've shot over the years, they've almost 99% been 55gr.

Even if he was interested in a SHTF scenario that the people on OTS like to talk about all the time, I was thinking that the vast majority of ammunition that you would find in stores, on the street, or at people's homes would be 55gr also, right?

So am I wrong to tell him that for HIS purpose, a 1:9 is prob the more accurate option because it stabilizes the lighter bullets better? Honestly, with his shooting skills he prob won't notice the difference in accuracy, but I thought this whole exercise made for interesting self-reflection on why I automatically choose the 1:7 whenever I look at a new upper.

[seb5]

I have all 1/7 and 1/8 and mostly shoot 55gr. For 55 and under 1/9 will not put him at any disadvantage. However the only reason I would go with 1/9 is if I planned on shooting lighter than 55 bullets for varmint shooting and such. I personally will not shoot anything less than 55gr so there is no reason to go with a 1/9.

[Failure2Stop]

Not in my opinion.
Since comparable barrels cost the same whether they are 1:7, 1:8, or 1:9, it's not like there is a cost benefit associated with twist changes. Add to that the fact that if he ever does decide to up his game he will be held back by the 1:9.

It seems to me that the most versatile twist rate would be a 1:8.
But that's just me.

[xjustintimex]

what exactly is the benefit of shooting a higher grain to a lower grain? why would a lower grain be preferable or a higher grain be preferable to some?

[ForTehNguyen]

what exactly is the benefit of shooting a higher grain to a lower grain? why would a lower grain be preferable or a higher grain be preferable to some?

the longer range and cover/armor penetrating 5.56 loads are the high grain

[Failure2Stop]

what exactly is the benefit of shooting a higher grain to a lower grain? why would a lower grain be preferable or a higher grain be preferable to some?

Short answer- the heavier/longer bullets tend to provide better precision and superior terminal effect in human tissue.
Smaller, lightweight bullets tend to be oriented toward varmint sized terminal performance, though some options in the 55gr area can be cost-effective for high volume training/practice.

Look around the Reloading and Ammunition sub-forum as well as the Terminal Ballistics sub-forum for specifics and post there if you have further questions.

[xjustintimex]

Short answer- the heavier/longer bullets tend to provide better precision and superior terminal effect in human tissue.
Smaller, lightweight bullets tend to be oriented toward varmint sized terminal performance, though some options in the 55gr area can be cost-effective for high volume training/practice.

Look around the Reloading and Ammunition sub-forum as well as the Terminal Ballistics sub-forum for specifics and post there if you have further questions.

ah thanks!

[Patrick Aherne]

If you are ever going to shoot frangible rounds, like in a shoot house, or on steel up close, 1:7 is the way to go.

[sundance435]

I have all 1/7 and 1/8 and mostly shoot 55gr. For 55 and under 1/9 will not put him at any disadvantage. However the only reason I would go with 1/9 is if I planned on shooting lighter than 55 bullets for varmint shooting and such. I personally will not shoot anything less than 55gr so there is no reason to go with a 1/9.

Is there a problem with 1/7 barrels over-stabilizing lighter rounds? I don't shoot anything lower than 55gr., so I'm curious.

[the_fallguy]

My 1 in 7 BCM has no problem at all getting center hits on a 3/4 scale steel silhouette at 300 yards with 55 or 62 grain ammunition. I have not seen any tendencies to key hole or tumble at any of the distances I have shot at with the 55 gr. in the 1 in 7 barrel.

The way I see it, if you want to shoot 62gr. and below, get a 1 in 9 twist. If you want to shoot 55 gr. and above, get a 1 in 7 twist. If somebody has any opposing views or experience on this matter I am certainly interested in hearing it. -

[Cameron]

I was pleasantly surprised to shoot a couple of sub MOA groups using a Federal 50gr HP bullet and a 52gr Hornady Match HP out of a 7" twist rifle. I would certainly advocate the 7" twist for serious use rifles that will shoot rounds from 50-80grs.

Cameron

[sundance435]

My 1 in 7 BCM has no problem at all getting center hits on a 3/4 scale steel silhouette at 300 yards with 55 or 62 grain ammunition. I have not seen any tendencies to key hole or tumble at any of the distances I have shot at with the 55 gr. in the 1 in 7 barrel.

The way I see it, if you want to shoot 62gr. and below, get a 1 in 9 twist. If you want to shoot 55 gr. and above, get a 1 in 7 twist. If somebody has any opposing views or experience on this matter I am certainly interested in hearing it. -

1/9 is okay for anything up to and including 69gr. I'm not sure how it performs with Mk262 type rounds.

[xjustintimex]

i'm alittle confused as I was on hornady website and on this page
http://www.hornadyle.com/products/more_detail.php?id=130&sID=73&pID=3

it says 223 REM 60 gr. Intended for use in a 1-7"-1-12" twist barrel.
Performs optimally in a 1-9"-1-12" twist.

I was under the impression 60 grain was best in a 1-7 and wouldn't work as well in a 1-12 twist?

[TOrrock]

The length of the bullet has a lot to do with the needed twist.

A long bullet needs a tight twist to stabilize. SS-109/M855 has the steel penetrator, which weighs less than an all lead core, so the bullets are long, which need at least a 1/9" twist.

An all copper and lead bullet that's 60 gr. or so will typically be shorter and may stabilize decently in some 1/12" barrels. The old Winchester 64 gr. Power Point will usually do OK in a 1/12" twist.

Frangible needs the tighter twist because it's such a light, long bullet.

Here's the deal. You don't loose anything on a fighting carbine using a 1/7" twist. You can use 77 gr. bullets all the way down to frangible. If you were building a varmint gun to shoot 40 gr. gopher grenades, you'd want a looser twist.

[xjustintimex]

haha gopher grenades :p

still doing research on the twists I'm thinking a 1:7 twist might be in my future

[crazymoose]

It seems to me that the most versatile twist rate would be a 1:8.
But that's just me.

It's not just you. 1:8 basically stabilizes anything, and won't over-stabilize the lighter stuff. 1:7 is another one of those "the military has it, so I gotta have it too!" features. Same with the government profiled, M4-cut barrels. As a civilian, I shoot about as many tracers as I launch ****ing grenades, so both of these "features" are not only worthless to me, they actually detract from a rifle's functionality.

[Savior 6]

The way I see it, if you want to shoot 62gr. and below, get a 1 in 9 twist. If you want to shoot 55 gr. and above, get a 1 in 7 twist. If somebody has any opposing views or experience on this matter I am certainly interested in hearing it. -

Not an opposing view, but just want clarification for myself in learning the twist rates. By what you said, would you suggest a 1:8 twist if a person were to only use 55gr. - 62gr. ?


still doing research on the twists I'm thinking a 1:7 twist might be in my future

I've only seen this on intenernet heresay and such but isn't there supposed to be an optimal twist rate of 1:7.7, to which 1:8 is the closest and recommended as the best average?

[the_fallguy]

I haven't owned one, but I think that a 1 in 8 twist would probably be optimal. Kyle Lamb says so in "Green Eyes and Black Rifles", and Failure2Stop (who is usually right on the money with his recommendations, so I listen when he makes a comment) suggested it as well.

I just wish more mainstream manufacturers would offer barreled uppers in that configuration.

[Savior 6]

I just wish more mainstream manufacturers would offer barreled uppers in that configuration.
It's always nice to see more options from different prices ranges.

[JonnyVain]

Best all around in my opinion? Get a 1:8 dissipator barrel. ADCO has their Custom Cruiser. It's going to be chrome vandium I think (old was SS).

http://www.adcofirearms.com/acc/productLine_.cfm?brand=Adco%20Custom&product_category=Barrels

If he plans on having a solid FSB, this is the best type of barrel, 16" with full sight radius for better accuracy shooting irons.

The new ones are going to be a little cheaper than what's on his site right now.

[Todd.K]

The idea of "over stabilization" is a bit of a myth.
By spinning faster than "optimal" any imperfections of the bullet are magnified by a small amount. Remember those bullet imperfections are causing inaccuracy in a "perfect" twist, just a little bit less than a faster twist.

My 1/7 twist shoots the 36gr Varmint Grenade just fine and loves BH 52gr Match.

For a fighting carbine the ability to use better performing heavy bullets should be the deciding factor.

[Terry]

I have given this some thought recently as well.
Mainly, because when ammunition was harder to come by, I could get 45gr varmint loads.
I never bought any, but in a pinch, I think I would be best served by a 1/9 bbl.
I know individual bbl's very, but can you shoot 77gr better in a 1/9, or 45gr better in a 1/7?
I'm thinking strictly in an emergency type situation, not a well supplied training or military situation.
Nevermind, I guess it was just answered.

[5pins]

I have shot the Winchester .45gr in a 1/7 without any problems. IIRC it was very accurate.

I'm a little surprised that Todd is shooting 36gr Varmint Grenades without them blowing up.

[variablebinary]

Most of my guns are 1/7, with a couple of 1/9 thrown into the mix.

I shoot everything from 40gr to 69gr just fine. It's rare, that I shoot anything heavier

[edwin907]

I don't have a single round of ammo less than 55gr and don't see buying any.
My ammo stockpile is Q3131A, Q3131 (pre-98), Fed M193, Norinco 55gr, AE 55gr, Win STHP 55gr, IMI/LC/Win M855, BHBB 75gr, Hornady TAP 75gr, Hornady 5.56 TAP 75gr, and MK262 77gr.

My 24 Varminter is 1/9, all of the other barrels are 1/7 or 1/8 twist.
The SBR barrels are all 1/7 twist.

[SWATcop556]

The idea of "over stabilization" is a bit of a myth.
By spinning faster than "optimal" any imperfections of the bullet are magnified by a small amount. Remember those bullet imperfections are causing inaccuracy in a "perfect" twist, just a little bit less than a faster twist.

My 1/7 twist shoots the 36gr Varmint Grenade just fine and loves BH 52gr Match.

For a fighting carbine the ability to use better performing heavy bullets should be the deciding factor.

My findings have been the same. I've never had a problem with "over-stabilization" and I've shot as light as 40's through a 1/7.

I would rather be able to shoot the heavy shit if needed and go with a 1/7 or 1/8 than have a 1/9 and not be able to perform as well with heavier ammo.

I have seen more problems with 1/9's and heavier bullets than 1/7 and lighter rounds but YMMV. For an all around shooter I prefer a 1/8 but have no issues with a 1/7. I don't own a 1/9 anymore.

[rljatl]

Is there a problem with 1/7 barrels over-stabilizing lighter rounds? I don't shoot anything lower than 55gr., so I'm curious.

Over stabilizing is not the problem it was once thought to be. Modern bullet manufacturing techniques have improved to the point that bullets fly true even when "over stabilized."

In fact, the military is switching to 18" barrels on their sniper rifles because they have found there is no loss of accuracy if the barrel twist is changed from the previous standard of 1 in 12 to 1 in 10, the new standard for .308. Shorter barrels are better for getting in and out of vehicles and aircraft, especially with a can attached.

[Mark21]

Thanks everyone for the replies. This has been very informative, makes me more comfortable with what I own, and changes the advice for my friend. Thanks again.

[akxx]

The idea of "over stabilization" is a bit of a myth.

My 1/7 twist shoots the 36gr Varmint Grenade just fine and loves BH 52gr Match.


You're lying. We all know that shooting 36-grain bullets out of a 1:7 makes the bullet spin so fast that the barrel gets scorched and the bullets and barrel self-destruct! :D

Kidding aside, 40-grain and 50-grain bullets shoot VERY accurately out of my 1:7 barrels.

[Kentucky Cop]

I have been following this thread and am glad everyone has explained this to me. My department policy requires us to shoot 55 grain bullets in our rifles as "duty rounds". As a street cop, I wont see any difference in accuracy from say 100 yards or less using my 1/7 twist barrel......., correct?

[akxx]

I have been following this thread and am glad everyone has explained this to me. My department policy requires us to shoot 55 grain bullets in our rifles as "duty rounds". As a street cop, I wont see any difference in accuracy from say 100 yards or less using my 1/7 twist barrel......., correct?

Shouldn't be a problem at all. The primary issue with very light-weight bullets in a fast-twist barrel is bullet disintegration, but this only happens with very thin-jacketed bullets that are DESIGNED to be high-fragmentation such as the non-ballistic-tipped varmint bullets (i.e. Hornady SPSX).

55 FMJs are robust enough that they don't shed jackets mid-flight.

[xjustintimex]

whats the most accurate and best self defense round for 1:9 twist?

[uncrownedzebra]

whats the most accurate and best self defense round for 1:9 twist?

https://www.m4carbine.net/showthread.php?t=19881

try this

[6933]

Swat- Please limit the foul language.:p You now owe me a Shiner Bock. Oh yeah, drinking an Icehouse after a long day.

[SWATcop556]

I have been following this thread and am glad everyone has explained this to me. My department policy requires us to shoot 55 grain bullets in our rifles as "duty rounds". As a street cop, I wont see any difference in accuracy from say 100 yards or less using my 1/7 twist barrel......., correct?

My dept currently issues the Federal TRU in 55gr for our duty round. I can keep the rounds pretty tight around the eyes and nose on a silhouette at 100 yards. That's prone with a T1 out of an 11.5 BCM.


Swat- Please limit the foul language.:p You now owe me a Shiner Bock. Oh yeah, drinking an Icehouse after a long day.

Sorry, I always seem to **** something up. :cool:

I'll gladly buy you a Shiner if you promise to stop drinking Icehouse. :p

[Artos]

wow...my first ar was a pre-ban hbar and it would key-hole the 55 ball ammo every now and then??

I bet those 40gr and under pills in a 1/7 are like a little grenade when they hit a critter.:cool:

[akxx]

I bet those 40gr and under pills in a 1/7 are like a little grenade when they hit a critter.:cool:

Especially when you can load them to 3400 fps out of a 16" barrel! :D

[MistWolf]

You cannot "over-stabilize" a bullet. It's either stable or unstable. What stabilizes the bullets is the spin it has. If it's spinning so fast it's not stable, it isn't "over-stabilized" it's unstable.

Twist alone does not impart stability to a bullet. It's the RPM. A bullet needs a minimum RPM to be stable in flight. To get that RPM you must have the right twist and the right velocity. A bullet may stabilize fine in a 1:12 barrel that's 24 inches long, but not from a 14.5 inch barrel. That's because the velocity of the bullet is less from the shorter barrel and the bullet will exit at a lower RPM.

The trouble with tighter twists is bullet construction. With a frangible bullets are by nature fragile. At high velocities with the high RPMs imparted by tight twist barrels frangible bullets will fly apart from centrifugal forces.

My father developed a load for his 22-250 that was firewalled with a Speer bullet designed to explode when hitting prairiedogs at 223 velocities. Though the twist was rather slow in his Remington 788 (1:14 if I recall right) the velocities he was driving those bullets at had them near the edge of self destructing from the RPMs they were spinning. We called his loads the "Blue Streak Express" because they'd leave a faint blue trail of smoke behind them. We discovered that smoke trail was lead dust leaking out of the jacket from the stresses. That bullet was so close to self destructing that hitting something as light as sage brush caused it to rip apart. It caused jackrabbits to explode on impact.

The point of this is that a 1:7 twist may be what you want in carbine length barrels. It will make up for the RPMs lost due to the lessened velocity from shorter barrels

[akxx]

You cannot "over-stabilize" a bullet. It's either stable or unstable. What stabilizes the bullets is the spin it has. If it's spinning so fast it's not stable, it isn't "over-stabilized" it's unstable.

Twist alone does not impart stability to a bullet. It's the RPM. A bullet needs a minimum RPM to be stable in flight. To get that RPM you must have the right twist and the right velocity. A bullet may stabilize fine in a 1:12 barrel that's 24 inches long, but not from a 14.5 inch barrel. That's because the velocity of the bullet is less from the shorter barrel and the bullet will exit at a lower RPM.

The trouble with tighter twists is bullet construction. With a frangible bullets are by nature fragile. At high velocities with the high RPMs imparted by tight twist barrels frangible bullets will fly apart from centrifugal forces.

My father developed a load for his 22-250 that was firewalled with a Speer bullet designed to explode when hitting prairiedogs at 223 velocities. Though the twist was rather slow in his Remington 788 (1:14 if I recall right) the velocities he was driving those bullets at had them near the edge of self destructing from the RPMs they were spinning. We called his loads the "Blue Streak Express" because they'd leave a faint blue trail of smoke behind them. We discovered that smoke trail was lead dust leaking out of the jacket from the stresses. That bullet was so close to self destructing that hitting something as light as sage brush caused it to rip apart. It caused jackrabbits to explode on impact.

The point of this is that a 1:7 twist may be what you want in carbine length barrels. It will make up for the RPMs lost due to the lessened velocity from shorter barrels

Perhaps the most concisely accurate explanation I have seen on the subject. Well put!

[perna]

There are a ton of videos of 1/7" twists spinning bullets apart, 35-40 grain seem to easily spin apart not far after leaving the barrel.

[ST911]

Individual barrels have personalities, and the results they produce will vary. Given lesser grades and producers, the variance will be wide.

I know a Colt 6920 that will reliably ruin 55gr UMC FMJ at proximal ranges. Others that will do the same with lighter varmint rounds.

On the flip side, I know 1/7s that will shoot the varmint bullets well, including the 36s (BHA Varmint Grenade), 45gr, and 52gr.

I also know 1/9s that will shoot the 75s and 77s, including one which shoots the Mk262 extremely well at range.

There are those that need the 1/7, and the terminal benefits of 75gr and up. There are those who think they need it. There are those who will never know the difference. The bulk of most peoples shooting is economy training ammo in the ~55gr weight. Manufacturer production of lights to heavies is thousands to one.

I like having options, and prefer to buy 1/7s. If I didn't have them though, I'd still be fine with my ~60-68gr duty rounds.

[C4IGrant]

Over the past couple years I've upgraded most of my rifles to 1:7 twist rate because it was better at stabilizing the heavier rounds that I shoot occasionally.

But a (non-mil, non-contractor) friend recently asked what was best for him for an all-around AR. I thought about what I shoot: 55gr surplus, 55gr Prvi, 55gr S&B, 55gr LC, and so forth. I do have some 75gr TAP (maybe 300 rounds) for self defense, and I reload 77gr Matchkings once in a while for competitions, but out of the thousands of rounds I've shot over the years, they've almost 99% been 55gr.

Even if he was interested in a SHTF scenario that the people on OTS like to talk about all the time, I was thinking that the vast majority of ammunition that you would find in stores, on the street, or at people's homes would be 55gr also, right?

So am I wrong to tell him that for HIS purpose, a 1:9 is prob the more accurate option because it stabilizes the lighter bullets better? Honestly, with his shooting skills he prob won't notice the difference in accuracy, but I thought this whole exercise made for interesting self-reflection on why I automatically choose the 1:7 whenever I look at a new upper.


First question: Are you noticing an accuracy issue with 55gr ammo and 1/7 twist.

Second question: Do you realize that most 1/9 twist barrels use less quality materials and have a much higher chance of having an out of spec chamber?

I shoot 55gr ammo about 70% of the time out of 1/7 twist barrels. I have never had any issues with accuracy. So stick with 1/7 twist barrels.



C4

[akxx]

There are a ton of videos of 1/7" twists spinning bullets apart, 35-40 grain seem to easily spin apart not far after leaving the barrel.

Read the posts above yours. Phenomenon fully explained.

[Gunner777]

My 1/7 has been very accurate no matter what bullet weight I use. In fact with an CMMG 22lr conversion I'm getting 1/2 inch groups standing unsupported at 25 yards. IMHO the 1/7 is very versatile.

[MistWolf]

Individual barrels have personalities, and the results they produce will vary...Very true. Rifling isn't always cut to the exact twist. It can vary in either direction. You never know what bullets it will prefer, velocities it will yield and what accuracy it has until you actually shoot it

[Gunner777]

Agreed---in fact every gun has a personality. Even the same brand and caliber will vary some from gun to gun. I consider myself lucky with the CMMG I bought. It's more accurate than the last one I bought which was a Bushmaster.