1:7 v. 1:9 for 55gr/75 gr

[NavArch]

OK. I've got it that my 1:9 upper needs to be replaced by a 1:7 upper or be re-barreled if I want to move from 55 grain bullets to 75/77 grain bullets.

Here's the question: Once I do that, how accurate will I be shooting 55 grain bullets in the 1:7 barrel at 200-300 yds? I have what I will call "an adequate supply" of 55 gr ammo, and am not going to be able to completely swap it out really easily. Do I need two complete uppers in order to make the best use of my ammo supply?

Thanks.

[Iraqgunz]

I have never tested mine for accuracy. However, I can hit a steel pig at 220 easily with my 11.5" SBR. I also hit some steel a few weeks ago using my ACOG at 280 yards.


OK. I've got it that my 1:9 upper needs to be replaced by a 1:7 upper or be re-barreled if I want to move from 55 grain bullets to 75/77 grain bullets.

Here's the question: Once I do that, how accurate will I be shooting 55 grain bullets in the 1:7 barrel at 200-300 yds? I have what I will call "an adequate supply" of 55 gr ammo, and am not going to be able to completely swap it out really easily. Do I need two complete uppers in order to make the best use of my ammo supply?

Thanks.

[RWK]

Presuming all other things being equal, you shouldn't see any negative difference in accuracy.

[87GN]

If the wind is low, I shoot 55s at 500 meters sometimes. With good accuracy.

[Eurodriver]

http://img828.imageshack.us/img828/1179/50923489.jpg

[87GN]

http://img828.imageshack.us/img828/1179/50923489.jpg

My 1/7s shoot 45s and 50s without "spinning them apart"...

[bkb0000]

http://img828.imageshack.us/img828/1179/50923489.jpg

excellent.

still not a law of physics... i've gone as low as 45gr in 1/7s and still pulled <1.25. likewise, there's a couple dudes at my range who like to shoot 77smk through their 1/9 bushmaster, and get some of the tightest groups i've ever seen in the flesh. but this chart sums up the rule nicely.

[NavArch]

I sincerely appreciate the replies. It looks like I will re-barrel my upper to make it a 1:7, and then test across the wider range of bullet weights. If all is well, all is well. At that point, I'll take "yes" for an answer. ;-) If not, I'll look at building an upper around the still-really-newish 1:9 barrel.

[Failure2Stop]

Why don't you just test the ammo you intend on shooting before getting a new barrel?
There is a decent probability that it will work and it will give you a bench mark in case you are not satisfied with how it performs.
It's a lot cheaper than a new barrel.
Just sayin'.

[NavArch]

Why don't you just test the ammo you intend on shooting before getting a new barrel?
There is a decent probability that it will work and it will give you a bench mark in case you are not satisfied with how it performs.
It's a lot cheaper than a new barrel.
Just sayin'.

Yes. I realized that to be the best plan as soon as I had hit the "submit" button. If the range test is unsat, I will execute the re-barrel sequence.

[Molon]

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 barrels; one barrel with a 1:9” twist, the other barrel with a 1:7” twist. The first barrel used in testing was a 16” Colt HBAR with chrome lining, a NATO chamber and a 1:9” twist. 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. The longer barrel with the 1:7” twist was purposely chosen for the increased muzzle velocity coupled with the 1:7” twist. Both barrels had free-float handguards.

Accuracy testing was conducted from a distance of 100 yards following my usual protocol. 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 attached to the objective-bell of the scope. Naturally, the wind conditions were monitored using a Wind Probe. The set-up was very similar to that pictured below.


http://www.box.net/shared/static/xo4duzdgtp.jpg



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 also over-layed on each other to form a 40-shot composite group that had a mean radius of 1.01”. The two composite groups are shown side by side for comparison. So much for the often posted nonsense about 1:7” twist barrels making 55 grain FMJ bullets “unstable.”



http://www.box.net/shared/static/o03ufeured.jpg



http://www.box.net/shared/static/os7sq6bfj6.jpg





Quality 55 grain bullets can shoot superbly from a 1:7" twist barrel. Most 55 grain full metal jacket bullets do not fall into the quality category, so any comparison made using 55 grain FMJ bullets with heavier open tip match bullets is nonsense.

The 10-shot group pictured below was fired from a distance of 100 yards from a Noveske barreled AR-15 with a 1:7” twist.


http://www.box.net/shared/static/9p6kf1904l.jpg


The 3-shot group pictured below was fired from the same 1:7” twist barrel for the Internet Commandos in our viewing audience.


http://www.box.net/shared/static/choz3qrhxf.jpg




The next 10-shot group pictured was fired from a Krieger barreled AR-15 with a 1:7.7” twist using 55 grain BlitzKings.

http://www.box.net/shared/static/0fuxcv68qk.jpg


Barrels with 1:7" twists can shoot bullets as light in weight as 40 grains without issue, as long as it is a modern, quality 40 grain bullet, such as the Hornady 40 grain V-MAX.



http://www.box.net/shared/static/j598a57fgb.jpg




Here's another example of just how well a 1:7" twist barrel can shoot light weight bullets. While the group pictured below was fired from a distance of only 50 yards, it's a 10-shot group fired from a chrome lined, NATO chambered Colt barrel with a 1:7" twist using 52 grain Sierra MatchKings.



http://www.box.net/shared/static/kras1x3uyy.jpg



The 10-shot group pictured below was fired from a 20" government profile Colt barrel with a NATO chamber, chrome lining and a 1:7" twist. That's about as good as a group as you will see from this type of barrel and it did it with 55 grain BlitzKings.


http://www.box.net/shared/static/g3377t7o0z.jpg



A 14.5" Colt M4A1 SOCOM barrel,with its NATO chamber, chrome lining and 1:7" twist can shoot quality 55 grain bullets quite well.


http://www.box.net/shared/static/r9jgrq14zn.jpg


Yet another example of how well 55 grain bullets can do from a 1:7" twist barrel. This time from the 16" version of the Noveske N4 light barrel that is also chrome lined and NATO chambered.



http://www.box.net/shared/static/ubsv4o9vzk.jpg

[87GN]

*slow clap*

[NavArch]

My current set-up is a 16" mid length. A local shop can provide and install a Bravo Company phosphate finished 16" mid length with F-type front sight for $370. Can I expect MOA performance with 75-77 gr quality ammo with that choice? Any other reasonably priced suggestions?

[TEL76]

Bravo company is pretty good.

[vicious_cb]

The only problem Ive seen with light bullets and a 1:7 twist barrel was with 36gr varmint grenades.

[MistWolf]

Molon, very very well done. You have proved the wisdom my father had taught me since I was knee high to a grasshopper- Although one can make educated guesses as to performance based on the specifications of barrel & ammunition, one cannot know what the performance will be until shots are fired. Each barrel is a law unto itself.

I applaud you, sir

[NavArch]

Is there any benefit to spending the extra $ for a Sabre Defense barrel rather than a Bravo Company barrel?

Judging strictly from their online graphics, SD uses the M5 designation to mean a mid-length gas system. Did I get that right?

[298436]

Not all barrels are true twists. My Armalite M15A4 midlength 16" 1:9 was actually 1:8.75.

[Molon]

Not all barrels are true twists. My Armalite M15A4 midlength 16" 1:9 was actually 1:8.75.



That’s a very good point. I have a 1:9” twist Colt barrel that does quite well with 75 grain OTM loads out to 100 yards (though not as good as a comparable Colt barrel with a 1:7” twist.) Though I’ve never bothered to measure the twist of the 1:9” twist barrel, it is certainly possible that the twist is a little on the “tight” side of 1:9”.


Here are some results from the 1:9” twist barrel firing the Hornady 75 grain loads from a distance of 100 yards. Before firing the TAP rounds, I obtained a 10-shot control group using Sierra 52 grain MatchKing bullets. The group measured 1.01” and had a mean radius of 0.36”. This group is a fine example of the accuracy this barrel is capable of as I have duplicated these results numerous times in the past with this barrel.

Here is a pic of the control group.
http://home.comcast.net/~gocartmozart/52_SMK_control_load.jpg


First up for the TAP loads was the TAP FPD load. Using the Colt 16” barrel with the 1:9” twist I obtained three 10-shot groups from 100 yards that measured:

1.28”
1.65”
1.76”.

For comparison the three 10-shot groups of the TAP FPD load fired from the Colt HBAR with a 1:7” twist barrel measured:

1.08”
1.15”
1.18”.

Using my usual procedure of overlaying three 10-shot groups on each other using RSI Shooting Lab software I obtained a 30-round composite target of the rounds fired from the 1:9” twist barrel. The mean radius for this target was 0.48”. By comparison, the mean radius of the 30-round composite target for the TAP FPD load fired from the 1:7” twist barrel was only 0.37”. This shows a definite increase in group size for the rounds fired from the 1:9" twist barrel.

http://home.comcast.net/~gocartmozart/TAP_FPD_stability_comparison.jpg


Next, following the same procedures, I obtained three 10-shot groups of the 5.56 TAP load through the 1:9” twist barrel that measured:

1.44”
1.90”
2.06”.

For comparison the three 10-shot groups obtained from the 1:7” twist barrel measured:

1.16”
1.38”
1.45”.

As before, 30-round composite targets were compiled to compare the mean radii. The mean radius from the 1:9” twist barrel measured 0.54” while the mean radius from the 1:7” twist barrel measured 0.46”. Again we see an increase in group size for the rounds fired from the 1:9” twist barrel. (Keep in mind that the control group from the 1:9” twist barrel was right on par with the control groups from the 1:7” twist barrel.)


http://home.comcast.net/~gocartmozart/556_TAP_stability_comparison.jpg

[m4fun]

Awesome Molon!

I always believed from "reading" that 1/9 twist stabilizing stops at about 68/69gr bullets. I find it interesting folks with 1/9 barrels drilling holes with 75/77gr bullets.

More than a decade ago or so, 1/9s were that gap to stabilize the buku surplus 62gr bullets on the market(remember the only reason for the 1/7s in the A2s was for stabilizing the tracers)

[michael word]

One of the best informative post I have seen in a long time. I am now at ease knowing that my 1/7 twist barrel was not a bad decision. I always fretted about the decision concerning the fast twist with the light weight bullets for varmit hunting, due to what I have read. Thank You!

[dail621]

Outstanding job!

Thanks for all the information!

[Adam Pini]

Super informative. Thanks

[Iraqgunz]

The other day I was out shooting with markm. I brought the Noveske and the SBR. Someone out there had a laser range finder and lased the steel target up on the hill at about 293 yards.

I was able to consistently nail it using the SBR with suppressor in place, using Hornady 55gr. TAP and my ACOG.

The Noveske also hit it with regular boredom which surprised me because we had zeroed it previosly with Prvi Partizan 75gr. match ammo.

[Molon]

The only problem Ive seen with light bullets and a 1:7 twist barrel was with 36gr varmint grenades.

Keep in mind that the Varmint Grenade is not a lead-core bullet.

[rainman]

Why don't you just test the ammo you intend on shooting before getting a new barrel?
There is a decent probability that it will work and it will give you a bench mark in case you are not satisfied with how it performs.
It's a lot cheaper than a new barrel.
Just sayin'.

Well worth trying what you currently have with the heavier bullets. I have a 1:9 Colt 16" HBAR that shoots 55gr military ball and 75gr Hornady TAP with great results.

A friend has the indentical upper...his doesn't handle 75gr TAP.

Bottom line: you won't know unless you try.


-Rainman

[Spoon]

I was having some pretty good results today with my 1/7 BCM 14.5in A2X pinned upper. 50yd zero, 55gr Hornady .223, 4moa Aimpoint, my dad spotting, and a decent hold over I was getting consistent hits out to 500 meters on steel plates. Fun stuff

http://img197.imageshack.us/img197/1849/60249490780557655564407.jpg

[BDavis]

OK, I gotta ask, why not use a 1:8 barrel? It looks like that would cover all the bullet weights in question. Am I missing something?

[MustangGreg66]

Lots of good info here. I always wondered about over-spinning lighter bullets with the faster twists. I started shooting .223 at varmints out of a bolt gun, 50gr V-maxes are hard to beat... I havn't tried it in my ARs, I guess I'll have to see what happens. I had to swap to the Varmint Grenades here in Cali because of the condor-no-lead zone.... I'll have to see if they'll hold up in my AR as well, I'm running 1:9 barrels... no rational there, just what I ended up with.

[Molon]

Lots of good info here. I always wondered about over-spinning lighter bullets with the faster twists. I started shooting .223 at varmints out of a bolt gun, 50gr V-maxes are hard to beat... I havn't tried it in my ARs, I guess I'll have to see what happens. I had to swap to the Varmint Grenades here in Cali because of the condor-no-lead zone.... I'll have to see if they'll hold up in my AR as well, I'm running 1:9 barrels... no rational there, just what I ended up with.

The Hornady 50 grain V-MAX bullets shoot quite well from AR-15s with 1:7" twist barrels. With only minimal load development, I turned in the 10-shot group shown below from a distance of 100 yards.

http://www.box.net/shared/static/9x267cj7v3.jpg


Here's a 50 grain V-MAX group for the Internet Commando's in our viewing audience (fired uphill, in the rain, no less!:D)



http://www.box.net/shared/static/ezgztgy0r2.jpg

[Alpha Sierra]

Molon, your posts are a breath of fresh air.

It is exaperating to continually see the same level of misinformation re light bullets in fast twists over and over despite posts like yours.

[cbyrd556]

Thanks Molon for the great post, it definitely cleared up my questions on the matter. Just goes to show that we can read and speculate all we want but rounds down range matter most.

[MustangGreg66]

"Shooting uphill in the rain", is that anything like walking to school in the snow? Uphill both ways? lol, I joke, but that second group is just awesome. The other guys are right, people can say whatever they want, the proof is in the pictures. Thanks

[ForTehNguyen]

so much for 1:9" not being able to hit anything with 75gr+, despite what the internet says. Not optimal but not the end of the world like a lot of people try to make it out to be.

[Alaskapopo]

OK. I've got it that my 1:9 upper needs to be replaced by a 1:7 upper or be re-barreled if I want to move from 55 grain bullets to 75/77 grain bullets.

Here's the question: Once I do that, how accurate will I be shooting 55 grain bullets in the 1:7 barrel at 200-300 yds? I have what I will call "an adequate supply" of 55 gr ammo, and am not going to be able to completely swap it out really easily. Do I need two complete uppers in order to make the best use of my ammo supply?

Thanks.
http://i59.photobucket.com/albums/g299/355sigfan/AR%20style%20rifles/NoveskeDesc.jpg
My 1/7 twist Noveske shoots 52 to 55 grain ammo just fine. It also shoots 77 grain loads great too.
http://i59.photobucket.com/albums/g299/355sigfan/Noveske%20N4%20targets/52graingroupwithNoveskeh335.jpg

http://i59.photobucket.com/albums/g299/355sigfan/Noveske%20N4%20targets/N135group1.jpg

In fact my 1/7 twist Noveske shoots ball better than my 1/8 twist Larue. It also shoots better than the Laure with 52 grain match bullets. The Larue however kicks its but with 77 and 75 grain bullets.
http://i59.photobucket.com/albums/g299/355sigfan/AR%20style%20rifles/Laruedesc.jpg

http://i59.photobucket.com/albums/g299/355sigfan/Noveske%20N4%20targets/NoveskewithBallammo.jpg

http://i59.photobucket.com/albums/g299/355sigfan/Larue%20Stealth%20targets/LarueBallgroups.jpg
http://i59.photobucket.com/albums/g299/355sigfan/Larue%20Stealth%20targets/Laruegroups4-27-10.jpg

[Iraqgunz]

I am pretty sure that if you look at many posts here (and I think Molon will agree) that it is not 100% across the board.

Yes, some or even many will. But, it is not always the case and you may be the lucky guy who gets the one that doesn't. I an addition most 1/9" are not HP/MPI tested.


so much for 1:9" not being able to hit anything with 75gr+, despite what the internet says. Not optimal but not the end of the world like a lot of people try to make it out to be.

[Molon]

I am pretty sure that if you look at many posts here (and I think Molon will agree) that it is not 100% across the board.

Yes, some or even many will. But, it is not always the case and you may be the lucky guy who gets the one that doesn't. I an addition most 1/9" are not HP/MPI tested.

Absolutely and I clearly stated that while I haven't measured the exact twist of the "1:9" inch twist barrel that I fired the 75 grain OTM load from, that it is quite possible that the twist of that barrel is on the "tighter" side of 1:9". Also keep in mind that those groups were fired in a Michigan summer. The results might have been entirely different in a Michigan winter. I would not "bank" on a 1:9" twist barrel adequately stabilizing the 75-77 grain bullets.

Here's a pic of the Hornady 75 grain A-MAX fired from another 1:9" twist barrel at a distance of only 25 yards.

http://www.box.net/shared/static/0n9igns8zi.jpg

[Molon]

"Shooting uphill in the rain", is that anything like walking to school in the snow?


With no shoes on!:D

[cbyrd556]

I an addition most 1/9" are not HP/MPI tested.

So true, this has been what led me to get rid of my 1/9 upper I put on my Franken AR before I joined this site and became better educated. As you stated IG there are exceptions, as there is with most things in life.

[6933]

Glad to hear I'm not the only one saying SBR's can be accurate much further out than most people think.