what weight bullets for a 1:7 twist AR?

[Pony Express]

Hey everybody,
Just wondering what the minimum bullet weight would be for a 1:7 twist AR. I have been shooting 55 grn bullets but I'm worried about premature throat erosion and Im going to switch to a heavier bullet. I have heard good things about the 75 grain ammo but for the most part it is pretty expensive. will a 68/69 grn bullet work just as well?

Thanks

 

[Canuck-IL]

Bullet quality is more relevant than just the simple weight ... 52gr SMKs are often used in fast twist barrels for reduced course shooting. If the projectile doesn't vaporize (30 - 40 gr varmint bullets), it'll just be a matter of what the gun likes. 69s should be fine.
/Bryan

 

[tju1973]

I shoot everything from 55 grns-77grn. I have a good friend that is going to do a small bath of 90 grain stuff for me to try, but for plinking? 55grn SP-- I do like 62 Grain Silver Bear HPs though-- -cheap, and has never given mine an issue.

 

[TonyAngel]

Shoot what you want to out of it. A 1:7 barrel shouldn't have any problems with 55gr bullets. Or 45gr bullets for that matter.

 

[Mr. T]

With that twist rate I would shoot 75 grain or 77 grain rounds. I've heard others complain that 1:7 twist rate barrels will spin the jackets off of anything under 55 grain rounds. Most of the guys at the range won't go under 62 grain rounds on twist rates like the 1:7.

 

[M1key]

1:7 is a good excuse (reason) to shoot the heavier bullets...

 

[rozziboy18]

mr.t+1
i had a 1:7 twist 20'' ar 15, i couldent figure out why i wasent hiting the target at 50 yards with 50 grain walmart grade ammo the day i bought it, it finaly dawned on me when i got to 15 yards off the paper and figered out that i turned my ar into a very small shot gun.


o and 69 75 77 80 90 grain bullets 77-80 should be about right

 

[briansmithwins]

I've run 50gr varmint rounds thru my 1/7 ARs with no problems. They wern't as accurate as the 75gr OTM but they made holes in the target at 100 yards.

OP, why do you thing that lighter loads are going to erode your throat faster? BSW

 

[benEzra]

OP, why do you thing that lighter loads are going to erode your throat faster? BSW

Also, the cost difference between 55gr and 69-77gr loads will pay for a brand new barrel well before the old one begins to show significant throat erosion, even if there was a difference in erosion rates (which I would like to see evidence of).

Hotter loads will cause more throat erosion than milder loads, but I don't know that typical commercial 55gr loads are necessarily hotter than 69-77gr loads.

As to the OP's question, anything 55gr and up is good to go in 1:7 barrels. You might can get away with slightly lighter bullets than 55gr depending on your velocity and actual twist rate (i.e., is your nominally 1:7" barrel 1:6.5" or is it 1:7.4", since they do vary between manufacturers and few are exactly 1:7.0").

 

[TonyAngel]

The only "problem" you are going to have with a 1:7 barrel and lighter projectiles is when trying to shoot the really light bullets or lighter bullets with thin jackets. They MAY vaporize when leaving the barrel.

I've never seen or heard of anyone having issues with accelerated throat errosion due to firing lighter projectiles. Considering the range of bullet weights that .223 projectiles are available in, 55gr isn't all that light anyway.

You haven't mentioned which 1:7 barrel it is that you have. I know lots of guys, myself included, that have had good success with 52gr hollow points in fast twist barrels.

Again, since your original question was with regard to bullet weight and possible accelerated wear, I will say don't worry about it and shoot what you want.

If you try a load and it vaporizes coming out of the barrel, then don't use that load again. Nothing will get hurt.

 

[MIL-DOT]

From all the digging around that I've done, 55 gr. and up for the 1:7.
I recently got a 1:7 Spikes mid-length. and 55 gr. Lake City has been great out to at least 100 yards ( haven't shot farther) . It also likes the 62 gr. Silver Bear.
Again, from what I've read, I wouldn't shoot anything lighter than 55 gr. through a 1:7, but Tony's report of good results with 52 gr. is good to know.

 

[TonyAngel]

If you want to test it out, go to Walmart and get a box of the Winchester 45gr Varmint rounds. They go for something around $20 for 40 rounds, or something there abouts. If you take your 1:7 AR and scope it and then try to run a bunch of M193 through it and get bad results, don't come to the conclusion that the barrel won't shoot light bullets. M193 is crap ammo, in terms of accuracy and if you can get a 2" group out of it, you're doing really well. The same goes for M855. Military ammo is meant to go bang every time while being used to shoot at people, not for shooting tight groups.

I actually get better accuracy out of Silver Bear 55 and 62gr steel cased ammo. The only way to test accuracy is to use good ammunition.

 

[Canuck-IL]

Again, from what I've read, I wouldn't shoot anything lighter than 55 gr. through a 1:7...

You need to pay attention - length matters and, yes, it's correlated with weight but not one-to-one - simply saying "nothing under 55" is simplistic. Most 55s are relatively crap bullets (Hornady FMJ being among the better) - try a 52 SMK from any twist 1:9 or faster and you'll have a different perspective.
/B