AR-15 Barrel Twist Question (NooB)

[MoDerN_WarRioR]

Ok soo... my AR-15 is a 16" 5.56 cal. 9/1 Barrel twist (Noted on the barrel)

Now i haven't really done any research on barrel twist yet because i am still fairly new with AR's but i am wondering...

1.) I usually shoot 5.56 55g bullets, so what is the max my 9/1 barrel can handle?

2.) What in the heck is the difference of the different ratio's of barrel twists.

I don't know a thing about barrel twist so i honestly don't even know what it is... Does it have to do with the rotation of the bullet? or the velocity?

If anyone at all have like a guide to Barrels for Dummies... Let me know where i can get a copy Any information would be great help! Or if there is already a post about this can some one link it to me?

Thanks for the help!!!

 

[KW]

1 in 9 indicates one turn in 9" of barrel. So a 1 in 7 would be faster, 1 in 12 slower etc. Generally 1 in 9 will stabilize up to 69gr, but some have good luck with heavier 75 and 77gr rounds. YMMV. Technically it's the length of the projectile and not the weight that is important, but generally a heavier bullet will be longer (and thus require a faster twist) in a given caliber.

 

[MarineOne]

Think of it like when you throw a football. If you don't put enough spin on it, (under-spun or under stabilizied) it will wobble really bad.

Now you can't really over-spin a football, but the best way I can think to describe overstabilization would be a rocket with fins that stabilize it in flight through the atmosphere. Once it hits the outer reaches of the atmosphere, there is less air mass (thinner due to altitude) and therefore less force on the fins. This would cause the rocket to flip over and come down bottom first, and the fins would try to correct the rocket's direction causing the rocket to tear itself apart.

Of course with a projectile there is somewhat more leniency with spin rates based on projectile weight. You could shoot a 55g through a 1:12 barrel all the way to a 1:7, but you wouldn't want to do that with say a 75g. The 1:12 barrel will not put enough spin on it, just like if you pushed a super light 40g through a 1:7 barrel and spinning it too much.



Kris

 

[MoDerN_WarRioR]

Ahh So this all makes sense to me now! Thank you very much for clearing it up for me.

Soo having a longer barrel say... 20" with a 1/7 twist would put a heavier bullet further out and straighter? BUT if i where to try to shoot a heavy bullet like a 75 grain with my current set up with the 1/9 twist basically the accuracy and the flight path would be shot to hell right? Like when i think of a wobbly bullet in the air, to me that is scary.

Also is there like a set way the bullet spins? Counter clockwise or clockwise? Or do all barrels differ? I was looking through my barrel and saw the twist or grooves that spin the bullet and it looked like it was rotating counter clockwise.

Thanks!
-Chris

 

[dagger dog]

There are rules of thumb that apply to this in that heavier bullets require more spin (twist), but really it is longer bullets require more spin, and as bullets go longer usually equates into heavier, but not always, looking at thumbs if in doubt, overstabilize the bullet by over rotating. So you can still shoot 55 gr FMJ out of your 1-9 0r 1-7 twist, if the bullet is made to with stand the rotational forces (strong jacket). Right or left spin makes no difference .

You will find a lot of the manufactuers will state the best twist for their bullet on the package or advertisement. Some of the varmint bullets with thin explosive jackets and sintered metal cores are exceptionally long and light for the length of the bullet. If in doubt over rotate.

 

[MoDerN_WarRioR]

Thanks everyone for Clearing that up for me.

One more thing... What are the advantages of using a longer (heavier) grain bullet like a 69g. or a 75g?

From what i know now it goes further but, is it the stopping power, or the accuracy or what? Is a bigger bullet like a 69 or a 75g. better for a specific reason other than the obvious... BIGGER is BETTER.

If i where to go hunting with my AR... what would a 55g. take down and/or what would a 69-75g. take down? I know shot placement is key factor but i know it would be extremely hard to take an elk down with a little AR LoL

I'm full of questions because i need to know what i am dealing with here! Thanks for your time!

 

[Canuck-IL]

Heavier bullets buck the wind better - at 600, ARs generally use 80 or 82gr bullets. Some have fooled with 90gr VLDs but they haven't panned out so far.
/Bryan

 

[C-grunt]

The heavier bullets start out slower but lose less velocity over time due to bigger mass and the longer bullet being more aerodynamic. Thus any cross winds will have less effect on them. Also a bullet becomes unstable and therefor less accurate when it crosses back under the sound barrier. The heavier/longer bullets, generally, stay super sonic longer than the light weight bullets and are more accurate at range.

The longer bullets tend to yaw more consistently than the lighter shorter bullets. The bullet yawing and breaking apart are the main damaging forces of the 5.56 bullet, outside hollow points or soft tips.

As far as hunting here in AZ, pretty much any weight .223 will work on the small stuff like coyotes. The heavier grain stuff would probably work on the southern AZ deer but I dont know if its legal or not, probably not. Any of the bigger game up north, it would be way to light to hunt with.

 

[MoDerN_WarRioR]

Man that's a big bullet! Do 80-90 gr. bullets require special magazines? i heard some one at the range saying that you have to hand feed the higher grain bullets because they are literally too long to fit into a standard 30rd magazine. Is that true too?

Or do they make special magazines for longer .223 bullets?

 

[MoDerN_WarRioR]

C-Grunt nice to meet a fellow AZ'er

Ya i was just thinking of small game up to coyotes at the max. Maybe some rabbit, or ground critters. Just to have a little more accuracy with moving targets. .223 might actually be a little excessive for rabbits so i might stick with slightly bigger game like coyotes.

Grunt do you know off hand if there are any limits or laws against shooting coyotes here in AZ?

I once heard from a friend that coyotes pretty much had bounties on them, like you kill one and you get some cash for it... If that where true... i think i found my next career path!! Hahaha

 

[C-grunt]

Im pretty sure they are open all year long. I have heard the bounty thing too for the pelts. But from what I have heard its only a few bucks. Go to a local store and find out the laws first. Im not an avid hunter.

 

[MoDerN_WarRioR]

Cool thanks Grunt! Ya.. im not a hunter what so ever either. Actually... have never once been hunting with a gun. Only Bow. (Never got Any thing..)

But any ways, Thanks for ur help man!

 

[Canuck-IL]

Or do they make special magazines for longer .223 bullets?

Those bullets are designed specifically for single loading and a relatively (for an AR) small jump to the lands. Single loading is not an issue as long range is shot slow fire.
/B