lol so a 1/7 is the best twist regardless of ammo or bullet weight? the answers keep getting better

what is the name of your new range and where in FLA is it?

Twist rate doesn't have much effect except when there's not enough.

50gr VMAX at 100yds from a 5.56 "1:7" that I've measured at 7.7. 6:00 Ten, 3:00 X, 11:00 Nine, settled into 2:30 X-ring, after 6 shots gave it a click left, and should have come a click down. Even with adjustments that's about 0.47 MOA mean radius.
Attached File


75gr at 300yds "rapid fire" from the same barrel, with a 4 MOA red dot. X-ring is 1 MOA diameter. I recall 8mph half value wind and I neglected a 1 MOA click.
Attached File

There’s a ton of bad info on twist rate. As long as you’re not under stabilized you’re good. A 1:7 will shoot everything and a 1:8 will shoot almost everything.

His measurements were 8.8-9.1. Assuming true 9 at sea level, that's an SG of 1.15, where 1.5 is ideal.

Absolutely.  It really is this simple.

Geez you guys....c'mon.

Get two (or even better, three) uppers and be done with it.

After the realization that 99% of my shooting has been with 55gr M193, 62gr M855/SS109, and various types of 55gr .223...I'm fine with 1/9.

They're not dropping out of the sky as others suggest. Are you looking to win matches or have "combat" accuracy. They are two different things. In the latter case most anything works and 1/9 is fine. The 20" heavy barrel match bullet shooting guys I think just like to boast.

My 10.5 did best with 69gr match ammo despite the fact that ARFcom suggested that a 10.5 with a 1/9 twist was useless. With ball rounds the groups were twice as big but hitting squarely where intended.

I'd personally go 1/8 if you can. 1/7 is fast for most purposes unless you're mostly shooting long, heavy bullets at long range. 1/9 is good if you're mostly shooting the (previously) commonly available surplus and FMJ ammunition.

There is zero downside to a 1/8 twist in an AR. It will not produce larger groups. While too much twist rate CAN have a negative impact on accuracy, the effect is infinitesimal. MANY other things will effect it more. If we are talking chrome lined 5.56 chambered 1/9 vs a stainless Wylde chambered custom 1/8 barrel, the stainless 1/8 is going to crush the 1/9 about 99% of the time with ANY ammo. There is also little impact with 1/7, but no real reason to select it over 1/8. The difference in accuracy with 55 grain or less is so small as to be lost in the barrel to barrel variance. Remember the higher the twist, the more effect bullet non concentricity or jacket non uniformity is amplified. Better bullets have less negative effect from high twist. A perfect bullet has none.

One thing about Wylde chambers is that if you ever decide to shoot steel cased stuff in a pinch...they tend to not like them.

For best reliability go 5.56 chamber...again...unless you're looking to squeeze out that last bit of accuracy.

Stainless barrels have the poorest life, but can have the best accuracy...all other things equal. A chrome lined, nitrided, or even chromoly barrel holds up better. There is no downside to nitrided barrels...they have similar durability to a chrome lined barrel so long as they're not abused in sustained full auto use, and the accuracy of a non chrome lined barrel. They just look a little funky. Choose what fits your application. Are you shooting a tiny target at 500 or just trying to hit center mass on a man sized target?

This is still a good general guide.


For comparison most bolt actions are 1:12...optimal for use with 55gr (and under).

Attached File
Attached File

Yup.



An Accuracy Comparison of 55 Grain FMJ Ammunition
Fired From AR-15s With 1:9” and 1:7” Twist Barrels


"55 grain FMJ bullets are over-stabilized and inaccurate when fired from an AR-15 with a 1:7” twist barrel."

The Internet Commando


Statements such as the one above always seem to be proclaimed by the Internet Commando, without posting any valid, statistically significant data to support that these effects occur, or that if they do occur, that they do so to any degree that has any significant effect on the accuracy/precision spectrum involved with AR-15s firing M193-type ammunition out to distances of 100 yards.

By definition, an “unstable” bullet will have a gyroscopic stability factor of less than 1.0 at the muzzle.  A typical 55 grain FMJ bullet loaded in M193-type ammunition will have a gyroscopic stability factor of approximately 4.27 when fired from a 20” barrel with a 1:7” twist.

[CaptainObvious] 4.27 is not less than 1.0. [/CaptainObvious]

The following demonstration compares the results of firing four, 10-shot groups of the same lot of 55 grain Prvi Partizan M193 ammunition from two different AR-15 barrels; one barrel with a 1:9” twist, the other barrel with a 1:7” twist.  When chronographed from a 20” Colt M16A2 barrel, the muzzle velocity of this lot of PPU M193 was 3219 FPS with a standard deviation of 35 FPS.












The accuracy specification for M193 cited in MIL-C-9963F is as follows:

The average of the mean radii of all targets of the sample cartridges, fired at 200 yards, shall not exceed 2.0 inches.

These averages are from 10-shot groups fired from machine rested, bolt-actioned test barrels.  All things being equal (which of course they seldom are) this specification equates to a mean radius of 1 inch at 100 yards.



The first barrel used in testing was a 16” Colt HBAR with chrome-lining, a NATO chamber and a 1:9” twist.  This is the barrel found on the Colt 6721.  All of my free-floated Colt 6721 barrels have turned in sub-MOA 10-shot groups at 100 yards when using match-grade hand-loads.

The second barrel used in testing was a 20” Colt HBAR, also with chrome-lining, a NATO chamber and of course a 1:7” twist.  I've owned three of these barrels and they have all turned in 10-shot groups at 100 yards that hover just above one MOA when free-floated and shooting match grade handloads.  I purposely selected the shorter barrel with a 1:9" twist and the longer barrel with the 1:7" twist in order to exacerbate any possible statistically significant influence that the differing twist rates and intendent muzzle velocities might have on the precision of M193-type ammunition when fired at a distance of 100 yards.



Colt 16” HBAR






Colt 20” HBAR







Accuracy (technically, precision) testing was conducted from a distance of 100 yards following my usual protocol. The barrels were free-floated during testing.  The fore-ends of the weapons rested in a Sinclair Windage Benchrest and the butt-stock rode in a Protektor rear-bag. Sighting was accomplished via a Leupold VARI-X III set at 25X magnification and adjusted to be parallax-free at 100 yards. A mirage shade was used. The wind conditions on the range were continuously monitored using a Wind Probe. The set-up was very similar to that pictured below.






The Wind Probe . . .





Four, 10-shot groups of the PPU M193 were fired from the 1:9” twist barrel. Those groups were over-layed on each other using RSI Shooting Lab to form a 40-shot composite group. The mean radius of that composite group was 1.08”.  As with the 1:9” twist, four 10-shot groups were fired from the 1:7” twist barrel.  Those groups were also over-layed on each other to form a 40-shot composite group; the results were nearly identical to those obtained from the 1:9” twist barrel.  The  composite group had a mean radius of 1.01”. The two composite groups are shown side by side for comparison.







The entire test as described above was also conducted using a second 16" chrome-lined, NATO chambered Colt HBAR with a 1:9" twist and a second 20" chrome-lined, NATO chambered Colt HBAR with a 1:7" twist.  The ammunition used in this test was all from the same lot of Wolf 55 grain FMJ "Performance Ammunition."  

As before, four 10-shot groups fired from each barrel at 100 yards were over-layed on each other using RSI Shooting Lab and just as before, the mean radii for these 40-shot composite groups showed no statistically significant difference.







Quality, modern lightweight bullets of copper-jacket/lead-core construction can shoot superbly from AR-15s with fast twist barrels. Typical 55 grain FMJ bullets found in M193-type ammunition do not fall into the quality category.

The 10-shot group pictured below was fired at a distance of 100 yards using 55 grain Sierra BlitzKings from one of my Krieger barreled AR-15s.  The barrel has a 1:7.7” twist.  The group has an extreme spread of 0.439 MOA.













……


An Accuracy Comparison of M855 When Fired From AR-15s With 1:9” Twist and 1:7” Twist Barrels.







This test will compare the accuracy (technically, precision) of IMI M855 at a distance of 100 yards, when fired from an AR-15 with a chrome-lined, NATO chambered barrel with a 1:9” twist and an AR-15 with a chrome-lined, NATO chambered barrel with a 1:7” twist.  The IMI M855 is one of the most accurate and consistent loadings of all the M855 clones that I have tested.


IMI M855 is loaded with a 62 grain FMJ bullet with a cannelure. It also has a steel penetrator seated in the ogive portion of the projectile. This makes the projectile unusually long for its weight, as well as giving it a lower specific gravity. The ammunition is charged with "ball powder". The primers are sealed and crimped in placed. The bullet is also crimped in place and the case mouth is sealed with an asphalt sealant.





Chronograph data for the IMI M855 was obtained using an Oehler 35P with "proof screen" technology. All velocities listed are muzzle velocities as calculated from instrumental velocities using Oehler's Ballistic Explorer software program. All strings of fire consisted of 10 shots each.







This accuracy evaluation used statistically significant shot-group sizes and every single shot in a fired group was included in the measurements. There was absolutely no use of any group reduction techniques (e.g. fliers, target movement, Butterfly Shots).

The shooting set-up will be described in detail below. As many of the significant variables as was practicable were controlled for. All shooting was conducted from a concrete bench-rest from a distance of 100 yards (confirmed with a laser rangefinder.) The barrels used in the evaluation were free-floated. The free-float handguard of the rifle rested in a Sinclair Windage Benchrest with the aid of a Sinclair fore-arm adaptor, while the stock of the rifle rested in a Protektor bunny-ear rear bag. Sighting was accomplished via a Leupold VARI-X III set at 25X magnification and adjusted to be parallax-free at 100 yards. A mirage shade was used.  Wind conditions on the shooting range were continuously monitored using a Wind Probe. All rounds were fired from the magazine. Each upper was fired using the same lower.


The barrels used in this evaluation were both Colt HBARs with NATO chambers and chrome lining. The 1:7” twist barrel was 20” in length and the 1:9” twist barrel was 16” in length. I purposely selected the shorter barrel with a 1:9" twist and the longer barrel with the 1:7" twist in order to exacerbate any possible statistically significant influence that the differing twist rates and intendent muzzle velocities might have on the precision of the M855 ammunition.

The first barrel used in testing was 16” Colt HBAR with chrome-lining, a NATO chamber and a 1:9” twist. This is the barrel found on the Colt 6721. All of my free-floated Colt 6721 barrels have turned in sub-MOA 10-shot groups at 100 yards when using match-grade hand-loads.

The second barrel used in testing was a 20” Colt HBAR, also with chrome-lining, a NATO chamber and of course a 1:7” twist. I've owned three of these barrels and they have all turned in 10-shot groups at 100 yards that hover just above one MOA when free-floated and shooting match grade handloads.



Three 10-shot groups were fired from the upper with the 1:9” twist barrel in the manner described above. The extreme spreads for those groups measured:

2.72”
2.19”
2.24”

for a 10-shot group average of 2.38”. The three 10-shot groups were over-layed on each other using RSI Shooting Lab to form a 30-shot composite group. The mean radius for the composite group was 0.76”.



In the same manner as above, three 10-shot groups were fired from the upper with the 1:7” twist barrel. The extreme spreads of those groups measured:

2.14”
3.01”
1.71”

for a 10-shot group average of 2.29”. As before, the three 10-shot groups were over-layed on each other using RSI Shooting Lab to form a 30-shot composite group. The mean radius for this composite group was 0.68”.







….

Molon

As usual I appreciate your detail

^^^^what he said

Barrel construction and bullet quality will have much more of an impact than twist rate differences

I read all the comments, I check on my phone so its a pain to reply, thanks everyone (especially this person lol)

I qualified at 500 yards with an A1 with 1/12 and 55 grain bullets.

It didn’t bounce off the target or anything.  I’m sure it wasn’t that powerful at that range but still supersonic.

This. It's not that big of a deal. The shooter is typically more critical than the equipment.

A 1:9 will do fine for 55gr out to 300, but why limit yourself, as 1:8 will adequately stabilize any bullet that can cycle through an AR15 magazine.

I have a very accurate match/benchrest quality 16" AR15 barrel. It will shoot 52 grain Berger flat base target bullets like lasers at 100 and 200 yards - sub 1/2 MOA at 100, sub 3/4 MOA at 200.  Haven't shot that bullet at 300, but I'm sure it would be fine, but I'd likely have serious wind issues.

That same barrel can shoot Berger's 77 OTM and 80.5 Full Bore sub MOA at 500, and probably beyond by guys who are better than I at wind doping.

I think the 80.5 is probably as long as can be magazine fed.

Executive summary:  Get a good 1:8 match barrel.

You don't need 1:7 unless you are shooting bullets too long to magazine cycle or are shooting tracer rounds.

So 55gr out of a 1:7 would extend the range past 300 yards?

OP, don't listen to shit like this.

55gr can be shot to 400-500 very well.
If you are going to shoot 55gr at this distance you are better off with the slowest twist rate that will stabilize the bullet. Faster twists don't magically stabilize better after a certain distance is reached.

If you are shooting a bullet with a crappy BC the only thing that will help extend the viable distance of the round is velocity. And you'll pick up a little velocity with a slower twist barrel

Come on guys, this is ARFCOM, not the Benchrest Forum.  We all know that MORE twist is ALWAYS better, no matter what you are shooting.  
May I suggest moving up to 30 caliber, then get a 1:4 twist barrel from Pac-Nor.  That thing will probably win benchrest competitions with anything you put in it.


Tony

It is possible, easy. I've done it with my Colt 6720 and an RDS.

The idea that 1/7 is the best twist rate for all bullets no matter what is just silly.  There are bullets that they even tell you don't shoot out of a fast twist barrel.


"Designed for total frangibility upon impact, this lightly jacketed bullet should be used only in “conventional” twist rate barrels (1×12? or 1×14?). Use in fast twist rate barrels can result in bullet disintegration in mid-air!"

https://www.sierrabullets.com/product/22-caliber-50-gr-spitzer-blitz/


https://www.sierrabullets.com/product/22-caliber-55-gr-spitzer-blitz/


My dad used & still uses those in his 222Rem & can't even begin to guess how many gopher, prairie dogs & other assorted varmints he's vaporized out of his old BSA bolt action.   They are very accurate for him & they are absolutely devastating on varmints.  It was not uncommon for him to be able to get hits over 100 yards on a target only presenting an area not much bigger than a quarter or half dollar.  I know there are, or at least were back in the 80's & 90's other manufacturers who made similar bullets as well, not sure if anyone else is still making them nowdays besides Sierra.    Those faster rates might be best for the widest variety of weights but they aren't the best for all weights/types of bullets.

Those are premium specialty thin jacketed varmint bullets which is not what OP intended to shoot. You'll notice that same warning is not on the 50 and 55 grain blitzking bullets. You can go back and forth all day long but if you took all the bullets available for 223 the vast majority would be safe to shoot in a 1:7 twist.

i,d stick with what the military uses because in shtf there ammo is all you,ll be able to possibly get. jmo

Exactly this.

Nice setup!

What model Vortex and mount are you using?

@StraightMiataMan

To be clear, do not buy a 1:9.  Go 1:8.  Those of us with 1:9 do not need to ditch them, but may have problems with some heavy (actually long) bullets like 77 grain SMKs.  1:8 would be the better choice on a new build or complete upper or rifle.

Don't worry about 1:8 being less accurate than 1:9 with 55 grain bullets.  I'm shooting 52 grain flat base Berger Match bullets from a 1:8 twist 16" match barrel.  That is for 100 and 200 precision shooting at bench.  It is sub 1/2 MOA capable when I do my part.  It shoots similar groups with Berger 77 OTM, which is a bit longer than 77 SMK bullets and is used at longer distances because there is less wind drift effect beyond 300.

So, go 1:8 and know you can adequately stabilize any bullet that will cycle through an AR15 magazine.  You can go from 52 flat base to 77 OTM, even 80.5 Full Bore.  1:8 even stabilizes Hornady 35 grain NTX Superformance varmint ammo with sub MOA accuracy.

There's no reason to use a 1:9 twist.  It will only limit you from using heavier bullets.  I prefer 1:7 for everything.  My go-to loads use 69 grn SMK's, but I've shot 100-yd matches with 52 grn SMK's and 55 grn FMJ's and scored 198-199s / 200 prone.  They're still sub-MOA.

Which target?

I would go 1/7, I’ve shot plenty of right groups with a 1/7 and 55gr vmax. The quality of the bullet is going to make the biggest difference. I’ve shot 55gr bthp out to 400 out of a 1/7 and I was making hits. I will say that 55gr out of a 14.5 doesn’t have as much juice behind it as 75gr from a 18in.

With this image in mind, a lot of people would be really surprised at what twist their button rifled barrels actually measure out to.    Hint: often not nearly as close to 1:whatever as they expect it to be.

IMHO someone with a rifle that usually sees 55gr is much more likely to want to shoot 77gr in a pinch than something goofy like 40-45gr.  

If you're shooting 55gr bullets that are nice enough out of handloads that are good enough to notice a real difference in barrel twist, then you can probably afford more than one barrel.   For everyone else, going slower than 1:8 in an AR doesn't make much sense unless it's a special retro build and you feel you just have to.

The primary source of 1:9 cheerleading is still - just like it was for the last 20 years - people who already have one who are trying to rationalize why it's somehow a better choice for their application.   I'm not saying don't embrace the strong points if you have one, or waste time and money rebarreling a rifle you already have that you're otherwise happy with.

Back in the day, @ PISC, I was nailing bullseyes @ 500 yards w/an M16A1... a 1:12 barrel.

I couldn't shoot 55 grain accurately to 400-500 yards without devine intervention. I wouldnt even try. I certainly wouldn't spend money trying to make it happen. In my previous career I was considered a "sharpshooter" or "precision shooter", although we never went past 100 yards. Despite some professional training, I wouldn't even try for that distance with anything less than 77 grain hand loads from a minimum 16" barrel. There are ALOT of guys on here that are orders of magnitude better than me, but unless you're wiling to put the time (many years) and effort into it, I wouldn't even consider something like that.
All of my 556 and 300 blackout guns are solid builds with 1:7 twist from Colt, Aero, BCM, and Geissele.

Yes. For shooting to 400 to 500 yards you want a 1:7 twist shooting 77 grain handloads. Its pretty simple really

I have an 18" WOA barrel in 1:7.  Last time I was shooting at 500 yards, I only had PMC Bronze 55gr.  I was hitting prairie dog targets consistently.

Yeah, it's amazing that Marines with 1:12 M16A1s and M193 were ever able to qualify at 500 for all those years

Haven't checked arfcom in a hot minute, sorry for the late response - it's a Vortex PST Gen 1 2.5-10x32 MOA on a PRI High Mount. Really happy with the glass for the price I got it off of GAFS, but honestly there's better mounts out there, I've had this one come a little loose a couple times and you can't properly get a screwdriver on it to actually tighten in down (which ruins the point of having thumbscrews anyways).

@AstraPat