Bullet weights for 1/7 twist


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12Pump
October 17, 2013, 01:11 PM
Could someone tell me what they use for bullet weights when you have a 1/7 twist barrel? That's what I have. I googled this subject and found different answers so I don't know which one to go by. First, I heard anything 55 grains and up, and also 62-77 grains, while 1/9 is for 55 grains.

I'm mostly interested in shooting 55 grains, since that it the cheapest, which isn't cheap at all, but sure beats the price of everything above it.

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On An Island
October 17, 2013, 01:18 PM
What caliber?

ugaarguy
October 17, 2013, 01:20 PM
I'm assuming you're asking in regards to .223 Rem / 5.56 NATO cartridges since you just got your first AR-15.

You can shoot pretty much any .224" bullet weighing 80 grains or less in a 1:7 twist bbl. If you want to shoot really thinly jacketed varmint bullets you'll have to limit the velocity to avoid tearing the jacket.

MtnCreek
October 17, 2013, 01:21 PM
Any bullet weight (you may have issues with 90gr+ bullets, I don't know). For cheap plinkers, I use 55gr Hornady FMJ reloads.

Shooters Pro Shop has a pretty good deal on Nosler 77gr HPBT seconds right now. After shipping I'm a hair over $0.16 / bullet. Worth checking out if you reload.

12Pump
October 17, 2013, 01:31 PM
What caliber?

That info would have been helpful, right? My mind has been so one-tracked lately about AR15's that I forgot there's anything else out there! Caliber is .223.

You can shoot pretty much any .224" bullet weighing 80 grains or less in a 1:7 twist bbl. If you want to shoot really thinly jacketed varmint bullets you'll have to limit the velocity to avoid tearing the jacket.

Thanks! Sounds like 1/7 twist is pretty universal when it comes to bullet weights. People seem to like 1/7 most. Maybe that's why.

MtnCreek
October 17, 2013, 01:34 PM
AR15's

That limits your bullet selection, assuming you want them to feed through the mag. Not a complete list at all, but as a general rule 77gr HPBT's are as long a bullet that will feed through the mag. 75gr Hornady A-max will not. Anything shorter will work.

gotigers
October 17, 2013, 03:03 PM
My 1:7 likes all weights, but 68 through 77 shoot the best. SMK's best, Hornady BTHP then everytbing else. I have not tried Barnes or Nosler.

556by45guy
October 17, 2013, 04:30 PM
I've only shot 55/64/65/77gr (nothing lighter or heavier) out of my 1-7 AR, but it doesn't seem one weight shoots any better than another. My 55gr and 65gr handloads easily do 5 shot sub-MOA at 100m as do my BH 77gr.

Arizona_Mike
October 17, 2013, 10:21 PM
Generally overstabalization is much less critical than under. That said, I think the main reason the military standardized 1:7 is because of the very long M856A1 tracer which matches the drop of the 62-gr M855 steel tip. As far as dedicated marksman/sniper weapons in the US inventory the Mk 12 SPR did go with a 1:7 for the Mk262 77gr Sierra Matchking, but the Seal Recon Rifle chose 1:8 as being optimum for the same round, AND the Marine SAM-R uses 1:7.7.

One thing I've found from playing with the Miller twist formula or the long version of the Greenhill's formula is that air density (from both temperature and altitude) makes a huge difference without going to extremes of either.

I still think that 1:8 is probably the best civilian twist but you will probably not see major overstabalization effects with 55gr bullets.

Mike

gotigers
October 18, 2013, 08:16 AM
I didn't think you could over stabilize a bullet.

The 1:12, 1:14 twist won't stabalize the heavy stuff. 1:9 can be iffy stabalizing over 68 grains. I've never had a keyhole on paper shooting light ammo, <50gr, from my 1:7. they doesn't have good groups, but they bullets stabalize.

I have 2 1:8 twists as well. They seem to shoot everything well.

MtnCreek
October 18, 2013, 08:38 AM
^ Good reading below. I'd read where several folks mentioned over-stabilization and couldn't get my head wrapped around it. I found the below and I'm not saying I fully understand it, but I at least accept it. :) Despite the info below, I still think a Hornady 55gr FMJ fired from a 1:whatever twist AR is the best range fodder ever devised. :)

http://www.riflebarrels.com/articles/bullets_ballastics/bullet_imbalance_twist.htm

nastynatesfish
October 18, 2013, 08:41 AM
Mine will shoot 55gr so in about a 12" group. It does like the 68-69. Haven't tried any heavier though

joed
October 18, 2013, 12:14 PM
I've owned 2 rifles chambered in .223, one had 1:9" twist, the other 1:7" twist. Both did not like anything under 55 gr. The 55 gr bullet shot mediocre in my opinion and the 69 gr and up were very good.

Lots of people say they have not experienced the above with fast twist. I have and will only shoot the 69 gr or heavier stuff.

Robert
October 19, 2013, 10:33 AM
Mine shoots 55gr, 62gr, and 69gr just fine.

Arizona_Mike
October 19, 2013, 09:20 PM
You want the bullet to turn so that it will stays parallel to the bullet path which is an arc. An overstabalized bullet will try to stay gyroscopicly alligned with the barrel and will end up pointed somewhere in between. This small angle between the bullet pointing direction and movement direction causes excess drag and turbulance.

Mike

gotigers
October 19, 2013, 10:28 PM
At what distance? All of it shoots fairly well at 100 yards. What about past 300, 500, etc?

I feel a good quality heavy match bullet is the way to go for longer distance. The heavier bullet's retained energy for resistance to cross wind is a big help. The 1:8 and 1:7 twists will have a better chance at good results with the heavier ammo.

john wall
October 19, 2013, 10:58 PM
The 77 gr SMK w/c is a game changer past 300 yds in your rifle.

If you are going to shoot beer cans at 50 yds, anything will work.

For serious chores, Sierra's 77 gr offering is the way to go.

MtnCreek
October 21, 2013, 08:54 AM
The 77 gr SMK w/c

Why w/c? Standard (non cannelure) 77smk's and 75 HPBT's seem to do a fine job in AR's. Have you had problems w/ them or just using the cannelure bullets as an extra precaution?

HankC
October 21, 2013, 08:29 PM
I'm mostly interested in shooting 55 grains, since that it the cheapest
Stay with 1/9 then. May do better with 55 gr, bit higher velocity and less wear. Most people probably only shoot 55-62 gr anyway, really no reason to have 1/7 twist unless you want to shoot long distance. If you shoot long distance, you want longer barrel, so I say 1/9 if 16" carbine length.

ugaarguy
October 21, 2013, 09:30 PM
Stay with 1/9 then. May do better with 55 gr, bit higher velocity and less wear. Most people probably only shoot 55-62 gr anyway, really no reason to have 1/7 twist unless you want to shoot long distance. If you shoot long distance, you want longer barrel, so I say 1/9 if 16" carbine length.
He already has a 1:7 twist bbl. There are plenty of reasons for a 1:7 twist in a 16" bbl. They include the superior terminal ballistics of the heavy bullets, and the ability to stabilize the long for weight copper solids that are now required in some jurisdictions that have banned all lead ammunition for shooting on public land, and all hunting. The velocity and wear differences between a 1:9 and 1:7 twist are negligible. A 1:14 twist will stabilize a 55 grain bullet at sea level. A 1:12 twist will stabilize a 55 gr bullet in sub zero temps in the mountains. A 1:9 twist bbl on a .223 Rem / 5.56 NATO rifle does nothing better than a 1:7 twist does. If you want to shoot light bullets drop to a 1:12 twist.

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