1:7 barrels and "proper" bullet weight

[mjblucci]

Just got the ati that I've had on layaway for the last couple weeks and brought it home. Also grabbed a vortex strikefire 2 and mounted it for sighting in this weekend, I've been researching just abut every rifle, handgun, ballistics chart, ammo, etc., that has interested me for the last 4 year's since I bought my first revolver. This is my first ar15. I am not a competition shooter nor do I plan to be because of my poor eyesight. As I research what's best for my new friends diet, I read many reports that heavier bullet weight is necessary for accuracy in the realm of faster twist rates, which I don't doubt, but I must ask, do these reports even apply to a shooter like me? I look around and the most plentiful ammo out there is DEFINITELY 55 grain fmj followed closely by 62 grain. Some boxes are as cheap as they were ten years ago as older forum post suggest.. getting even into the 60+ grain weights starts to get expensive fast... would using a lighter/mid range bullet weight really be affected so strongly as to effect my goals in target shooting? I'm looking for foot wide groups at 100 yards... again I'm not a competition shooter looking half-inch groups. I don't even intend to shoot past that distance very often at all. What say you, the experienced ar gunner?

[mete]

If you're not going to get into serious target shooting then some things are not going to be a problem . While excessive twist may reduce accuracy a bit insufficient twist is going to have more effect to the point sometimes in that the bullet will tumble !Perhaps 45 to 70 gr weight should do fine in your rifle! Have fun.

[Pilot]

My 1:7 barreled Colt M4/LE6920 seems to shoot 62 grain M855 slightly more accurately than 55 grain M193. I compared Federal ammo side my side, and with the 62 grain I get sub MOA groups bench rested while the 55 grain opens up to around one inch, or slightly larger at 100 yards. For informal practice, I don't see this a significant.

[darkgael]

The 1-7" twist will shoot bullets up to 80 grains very nicely. It may well shoot lighter bullets well also. You will need to do some load development or buy a variety of different weighted factory ammo.
Pete.
Note: the 80 grain bullets....the resulting cartridge will not fit in an AR magazine and must be single loaded.

[Art Eatman]

As Pilot noted, a fast twist won't hurt you all that much with a light weight bullet, while a too-slow twist won't stabilize a heavy bullet.

From an ammo-cost standpoint when doing casual shooting, odds are that 55-grain loads would be the least costly.

[Ibmikey]

I guess I am the exception when it comes to twist hype, I own AR's with 1/7, 1/8, 1/9, 1/10, 1/16 twist rates. In the 5.56 rifles I shoot weights from 40 to 62 grains....they all shoot reasonably accurately for dirt clods and soda cans as well as paper punching in an informal style. Serious target shooting is a different matter but from your original purchases I should think plinking is paramount. I find out if the rifle shoots best with 55 or 62 gr, note it in a journal and then if ever I want to get serious I have a reference to ammo. In the winter up here accuracy is secondary to fun while shooting with layers of clothing topped by Carheart insulated coveralls (9 degrees out right now).

[bfoosh006]

Generic bulk Federal XM193, And Federal American Eagle will meet your requirements just fine. 2"-3" MOA groups are the norm.

But... if you order some online... I would suggest some of the Wolf Gold 55gr .223... it costs the same as the Federal stuff and has much better accuracy.

Better accuracy allows you to focus on your shooting skills ( trigger pull, etc )much more easily.

http://www.aimsurplus.com/product.as...=2135&fprdct=1

[kraigwy]

The 1:7 will shoot any thing up to and including 90 gr Bergers and shoot them well.

The exception is light thin jacket bullets designed for the Hornet.

77s are the heaviest that can be used from the magazine. 80 gr. and heavier need an OAL that requires they be single loaded which isn't a problem since they are used in matches fired at 600 & 1000 yards which require single loading anyway.

As an example the Army uses a Mann Device to test ammo. For the 223/5.56 the Mann device consist of a heavy short match barrel in 1:7.

The Army gives these Manns to ammo makers to check their ammo. A while back Lake City was not meeting the accuracy requirements the Army required. They blamed in on the Mann, saying it was defective. So to test the Mann several different loads was tried in the Mann issued to LC. The most accurate was a 25 gr. of 3031 pushing a 52 gr Sierra bullet.

Turned out not to be the Mann but LC's bullet seating which was corrected.

Long story but it points out that 1:7 does shoot light bullets.

The Mann I got from the CMP (Remington action, Kart Barrel)





In this picture I put my Mann in a stock for a little bench rest shooting.

[marine6680]

General use fmj ammo isn't going to be match grade accurate to begin with. So pick up the cheap 55gr and have fun. The 62gr stuff has the penetrator in it, and some ranges do not allow it. If your range does, buy up some of it too.

In that case, the difference between 2moa and 2.5moa isn't really important.


Now if you ever want to shoot for match accuracy, then the 1-7 twist may not like lighter stuff. My personal rifle will shoot lighter match ammo into 1.5moa but it will shoot less than 1moa for heavier stuff like 69gr and 75gr stuff.

Not enough difference for most people to worry over unless they are competing in a match.

[mjblucci]

As always, all of your responses have been most helpful in taking the confusion out of my latest acquisition. Some made it sound like I'd be outside the range of minute of man shooting xm193. The phrase "over-stabilize" is thrown around a lot. Even read a couple of times that bullets tend to shred or fragment in mid flight due to it. Most firearms are more accurate than I am in the first place. With the differences in accuracy stated here, I probably won't even notice.

[stagpanther]

I've shot everything between 55 and 72 gr through 1:7 for years with no issues (except for having to keep an eye on the higher BC big bullets --the COL and compressing of charges). My understanding is that the relationship between bullet weight and twist is not strictly correlated to what you "can or cannot" shoot--the actual bullet contact surface and spin/drag imparted is more relevant. Not sure what "over-stable" means-- but it is possible to spin a lightly bonded bullet so fast that any "wobble" can cause it easily fragment--I've heard tales of some bullets vaporizing in mid-air.

[Rimfire5]

My experience with a 1976 Colt H-BAR 1:7 twist is that the lighter 55 grain bullets do not shoot as accurately as the heavier 75 to 77 grain bullets.

It can achieve under 1 MOA at 100 yds with 77 SMK grain bullets and also with 69 grain SMKs and 70 grain Berger bullets with the right powder loads. Interestingly, 75 grain Hornady BHTP bullets won't do better than 1.7 inch groups at 100 yards.

55 grain ammo shoots around 2.5 inches at 100 yards.

This 1:7 twist likes heavier bullets and relatively slow powders like Varget, IMR4895, H4895, and CFE223.

[Bart B.]

Biggest issue with fast twist barrels shooting light bullets our really fast is their rpm number. Too high of a spin rate increases the centrifugal forces on unbalanced bullets. Maybe 5 to 10 out of 100 bullets may be "perfectly" balanced; the rest jump a bit off their exit angle when they clear the muzzle.

Bullet rpm equals muzzle velocity in fps times 720 divided by rifling twist in inches. 3000 fps with a 1:7 twist spins bullets 308,571 rpm.

[MarkCO]

I've seen 1/7s blow up light varmint bullets. We had a guy shooting 45 grain bullets in a AR15 at a 3Gun match, about every other bullet was a grey puff about 30 yards out.

1 foot groups at 100 yards would be terrible accuracy for 55s or 62s out of pretty much any AR15, so I would not worry about it much. Even for 3Gun, I won't suffer a rifle that won't put 55s and 69s under an inch at 100 yards and I typically look for 69s to be 1 " at 200 yards. If your stock tube is decent at all, 1" at 100 yards with 69s should be no problem for the gun.

[skizzums]

I also have the ATI with the 1:7, in indeed it likes like hornaday or ppu 75gr best, it's pretty darn accurate with anything I put into it. if your shooting less than 100 yards, I don't think you'll notice the difference, but at 100 the difference between 55gr SP and 75gr OTM is about an inch. which makes a big difference when shooting out to 200-500 yards. but if you do not handload, than those bullets really aren't feasible to shoot with any regularity, and 55gr does the job if that job doesn't include the tiniest groups you can get. it's clay pigeon accurate no matter what your shooting.

I have some 40gr v-max bullets that do great on pumpkins and apples out to 50 yards, I do not know how light you need to go, or at what distance they start to come apart, but I like em.

[KyJim]

Disclaimer: I'm no expert but I understand that twist rate is more intertwined with bullet length than bullet weight. However, heavier bullets are typically longer than lighter bullets so we can normally just refer to the weight of the bullet and not the length because that is more difficult.

All that is a preface to saying that if you're not satisfied with the 55 gr ammo, try the M855 type ammo which is can be found at nearly the same price as some of the 55 gr ammo. The M855 is 62 gr. and has a steel "penetrator" tip. Because steel is lighter than lead, the bullet is a little longer than either 55 gr ammo or other 62 gr ammo. It is part of the reason the military switched from barrels with a 1:12 twist rate to a 1:7 twist rate. The M855 is NOT "armor piercing" but you should double-check the laws of your state and locality to make sure it is lawful for you to own. Some ranges might also restrict use of this ammo.

Cross-section of rounds at: http://www.ar15.com/ammo/project/hist_milammo.html

[rickyrick]

I was a 1:9 man up until I ordered my new rifle kit. It's gonna be 1:7, I got a good price on a quality barrel by going with 1:7.... I trust what most of the people that post have to say...

My style of shooting the 1:7 will work just fine. I doubt id notice the difference. I still have my 1:9 mini14 if I varmint hunt again and need varmint grenades... I still may try them in the 1:7 and see

[bfoosh006]

After firing 10K + of rounds through 5 differnet 1n7 barrels, 2 1n9 and, 1 1n12 with mostly 55gr and 62gr.... I can say that the twist rate math results do not seem to really work in the real world. Accuracy from the barrels comes from quality of production.... not the "your twist rate is to fast".

I know most people don't want to hear this... but I have fired numerous light weight bullets ( 36gr-50gr ) and had excellent results with 1n7 barrels. The whole bullets flying apart from a fast twist was with some of the early varmint bullet designs.. ones made for 1n14 twist raes. The "correct" twist rate had no effect on AR15 accuracy at 100-200yds. As a matter of fact the Fed. AE .223 Tipped Varmint 50gr round fired through my 1n7 barrels is my accuracy standard. And always fires a group just barely over 1 moa.
I will admit that at the longer distance 200-500+ yds a heavier, more streamlined bullet is a far better choice... and this is where having the 1n7 twist is absolutely critical. To slow of a twist will cause keyholing.

But , for the AR world with its numerous barrel manufacturers... I do not believe that having the mathematically correct twist rate is critical for 64gr and below. I have seen FAR to more examples of 1n7 barrels shooting tiny groups with a "too fast" of a twist for light weight bullets.

Frankly, I feel the myth as far as AR's is just a convenient excuse from a sub par barrel, or AR15 maker.

Seriously.... do not bite to far into the twist rate sandwich... if you want to get down to brass tacks... all 1n14 twist barrels should shoot ALL 40-50gr bullets perfectly ! ... Right ?
And the same can be said for 1n9 and 1n7 twist rates.... you can see where this is going... there are far more variables then just twist rate involved in making a barrel shoot good.

For those interested... here is the Fed. AE 50gr I am talking about..http://www.sgammo.com/product/223-55...-ammo-ae223gtv

Try some yourself in your 1n7 twist at 100yds.... then fire some match 69gr 77gr or whatever and compare groups...

You will be surprised. ( And save a bunch of money )

Bottom line 1n7 will work with all the standard weights out there... 1n9 won't.

[tirod]

The reality is that some barrels shoot some bullets well. The problem is that the factory making that barrel didn't shoot it and tell you which was the most optimal.

Leaving the new owner to go buy ammo, shoot it, and then determine which worked the best for accuracy. One difficulty is getting the new owner out of the way - likely he's the reason for the group dispersion until he settles in and can shoot that gun consistently. At that, his skill level still affects the groups.

Which makes a good excuse to go shoot. The shooter gets better and he sorts thru the ammo to discover which is really the most accurate for his purposes. Which means he could find a load everyone else disparages that he and his gun can handle. It may or may not be affordable, tho, which is part of the bigger picture.

The same discussion is going on about what can shoot out of 1:9 barrels, the overall result of all these discussions is that for some one cartridge can work, but for another, it won't. Nobody knows until they try.

We can't really say for any certainty what your barrel will do. Too many variables, and those who assert otherwise aren't being realistic. I'd shoot the worst of the lot just to find out for yourself. It's good trigger time and you might be pleasantly surprised at what they do.