Looking to get some parts together for a new build for my son.  There are some good deals on 1:7 uppers out there...problem is my ammo fort is all 55g. with some 62g. and I don't want to start investing in 70g and up ammo.



Will the 1:7 twist provide good stabilization and accuracy for the 55g pills?  I've read lots of conflicting statements on this...first hand experience with this please respond.  Thanks.

Truth be told, you'll probably be better off with a 1/9 if that's the only bullet range you'll be shooting.

Should be fine. I shoot it fine.
See here...
http://www.ar15.com/forums/topic.html?b=3&f=16&t=503947

I shot alot of 55 gr out of my 1/7 and it is perfectly fine.

For those rates a 1/9 should be better. That being said a 1/7 should stabilize a 55gr ammo correctly. LMT sent me an rma because mine wouldn't(just got to them a few days ago).

I hear ya, but AIM is running Spikes Tactical COMPLETE uppers for $479...chrome bore too.  Only problem is they're 1:7...need to know if they are GTG for 55g.  

1:7 will work great with a 55gr FMJ bullet.  The only concern with a 1:7 twist barrel is if you start shooting varmint bullets where they have a thin jacket and perhaps also lighter weight.  Then the rotational stress on the bullet could cause the jacket to come apart in flight.  I shoot lots of 55gr FMJ ammo and all of my AR-15s in 5.56 have 1:7 twist barrels!

I just never shoot varmint bullets through them.

Thanks all for posting.  I had suspected as much that the 1:7 would be gtg for 55g (all milsurp, no varmint loads).



Is that Spikes Tactical 1:7 complete uppper for $479 as good a deal as I think it is??

Yes, when you consider a BCM complete upper is about $30+ more.

You will get better grouping with heavier (more correctly worded: longer) projectiles like 69gr, 75gr, 77gr… and that is just a simple, scientific fact.
1:7 IS a little fast for 55gr to “properly” stabilize (not implying that they are going to key-hole or fly off sporadically, but group size will be larger compared to the longer projectiles)

But, I run 55gr all the time out of my 1:7 barrels with no issues at all…
If you are shooting for groups, 55gr projectiles are not the optimum length to use in a 1:7 twist barrel, but if you are plinking, running a carbine class, engaging steel targets at 100yds and under…. 55gr will do just fine without killing your bank account.

What is supposed to happen if you go further? I've shot steel at over 500 yards with 55s and they worked just fine. Is something wrong with my setup? Should they be wildly inaccurate?

All depends on the size of the steel target I guess…
Are you really going to argue that 55gr is the optimum length projectile to use out of a 1:7 twist barrel?????

If it gives you the accuracy you need for a given situation, then yeah. We shoot matches with 55 grainers where we engage targets out to 300 all the time, and the bullets work great. Would a heavier, more expensive bullet that did exactly the same thing be more optimal in that case?

It's been shown many times that quality 55-ish grain bullets shoot very well out of 7 twist barrels.

Molon and many others would disagree with your "science".
he has posted reports of shooting less than 1MOA with 55gr blitzkings from a Colt M4A1 barrel LINK

the problem isn't the bullet length, it's the design of the round and the load. most of the 55gr XM193 style rounds as well as value pack "plinking" ammo are not loaded for accuracy and will shoot 2-4MOA. heavier bullets like 75gr TAP and the 69/77gr SMK are match grade rounds designed for better accuracy, it's not a factor of the twist rate.

I was more accurate with my 1x9 vs my 1x7 with 55 gr FMJ ammo but unless you are match shooting the difference wasn't huge. YMMV

Difference is likely more due to barrel differences then bullet differences.  There really is no such thing as too much spin as long as the bullet can stay together.  Nobody can prove it one way or the other unless you had identical bench barrels made (one in 1:7 and one in 1:9) and compare head to head.  Operator skill is likely to be a bigger factor then twist.

+1

Why would over stabilizing a bullet create worse accuracy, O wait it doesn’t.

My 16" chrome lined 1/7 twist Noveske shoots equally tight groups with 45 grain and 75 grain at 100 yards.  It will not shoot tight groups with XM193.

depends, some people say 55gr in their 1/7 sucks, others say its fine. This is why I prefer 1/9 I shoot 55gr

Ok, forget that pesky science stuff, bearing surface lengths, sectional density, ballistic coefficients, and well established ballistic formulas and lets rest all of our hopes on the fact that a guy who hand loaded some match grade 55gr ammo was able to produce groups that measure just over, just at and just under 1” at 100 yds out of a 1:7 twist barrel from a bench using a Leupold VARI-X III set at 25X.

Yes, that sounds like a great idea… you are right.

There is no possible way that if the same guy would have hand loaded match grade ammo using 77gr match kings under the same conditions that he would have shot ½ or even ¼ MOA groups because the fact that the length of the 77gr projectile is better suited for the 1:7 twist rate.

You know… I never stated that 100yds was the limit for 55gr out of a 1:7 barrel… I never stated that you couldn’t achieve decent accuracy with hand loaded, match grade ammo loaded with 55gr projectiles using a 1:7 twist; I simply stated that 55gr was not the optimum weight projectile for use out of a 1:7 twist barrel… and it’s not my opinion, that is a FACT.  

Off the shelf Hornady 55gr steel cased practice ammo yields larger groups than off the shelf Hornady 75gr steel cased practice ammo out of all of my 1:7 barrels… both are loaded the same using a steel case and I would hardly call either “match grade” or say that the 75gr was of a higher quality compared to the 55gr… the only real difference is the length and weight of the projectile…
Now I wonder why the 75gr would produce tighter groups???? Couldn’t have anything to do with any of that scientific mumbo-jumbo… or could it????

My Spikes middy (1:7) does not have good groups using 55gr, but loves the heavier stuff.



My CMMG 14.7" M4gery (1:7) loves everything.

Well, here is Eugene Stoner’s explanation of an “over stabilized” bullet,
Not that he would know anything about the rifle that he invented…

“As a bullet arches over its trajectory, its axis becomes imperfectly aligned with its direction of motion. Ideally you would like for aerodynamic forces to gently correct its attitude and bring its axis back into alignment. If the bullet is spinning too fast, it's over-stabilized, then the gyroscopic effect prevents this realignment from occurring. After a while the difference will become so great that the bullet will "lurch" unpredictably as it corrects. It's a detriment to long-range accuracy –– something you'd never see on paper at 100 yards, but out at say 400+ you might start to see it happen.”

Actually, Molon has talked about the science of it.  The amount of spin required to "overstabilize" the gyroscopic effect of a bullet is more than a 1:7 twist can manage on a 55 gr. bullet.  The differences you are likely getting in your own guns are likely due to the differences in the guns themselves (barrels, rails, harmonics, etc.) and not due to the difference in the bullets.

I have this upper and shoot 55 gr exclusively, except to find out how the heavier HD/SHTF stuff that I keep on hand does.  It stabilzes all 55 gr that I have shot just fine.  It's plenty accurate too.

75s of cource, but that was not the question in the first post!  The first post asked will 55gr bullets be fine out of a 1:7 twist barrel and they will!

The reason 75s are better in your example has more to do with sectional density, ballistic coefficient, and ability to maintain velocity which reduces time of flight an in turn reduces environmental effects.

Make this simple, you are only shooting at ranges under 100-yards.  Very, very few people would ever notice a difference between comparable 55-gr bullets out of a 1:9 or 1:7 trwist barrel.  The OP didn't ask what was a better match bullet, 55gr or 75gr!

Wrong forum and dupe - it's answered in the ammo forum FAQ.