AR15 twist rate and incidence of tumble...

[Klacktor]

Okay AR dudes.

What's the heaviest proj.(5.56/.223) you guys sucessfully send through a 1/7 AR barrel? (looking for personal experiences here)
I loaded some 70gr and I'm really not having any problems with them, actually quite the opposite, scoped I'm getting very small groups if not overlapping.

Do you think the twist rate/grain weight stigma is overstated or do you find heavier projectiles to need differing twist rates?

I'm considering building another upper with a 1/9, but if its no different I just wont bother. I'll say that I do use the rifle for varm hunting in ranges up to 400-500yds.

Thanks for any input.

 

[Klacktor]

I wrote that backwards =(

I HAVE a 1/9.
Considering building a 1/7 for the versatility.

oops.

 

[The_Hunter]

I had issues with my 1:9 stabilizing any other than 55gr. I have shot up to 70gr rounds out of my 1:7 twist bbl

 

[M. Sage]

I wrote that backwards =(

I HAVE a 1/9.
Considering building a 1/7 for the versatility.

oops.

Depends on how you define versatility. 1/9 will stabilize lighter bullets down to 40 grains or so and up to around 70. If you ever plan on firing lighter bullets, then the slower rate is for you. If you want to get heavy, 1/7 works great up to around 80 grains. You can even get barrels with faster rates for longer, heavier bullets. But these come at the expense of shooting lighter bullets accurately and faster barrel wear.

It turns out it's actually bullet length that determines optimal twist rate. However, since they're all the same diameter and pretty much the same density, heavier = longer.

Some good reading is found at the Ammo Oracle: http://ammo.ar15.com/ammo/project/perf_twists.html

 

[codygjohnson]

My 14.5" in 1/9 would stabilize hot 77 grain loads to at least 100 yards (furthest I ever shot them), but it's a real rarity to see one do that. I sure did take down a lot of hogs with that combo though...

 

[codygjohnson]

The 18.5" 1/8 on my precision AR will stabilize 77 grain to 400+ yards, but I get much tighter groups with 69 grain, so thats what she gets fed.

 

[MR Redneck]

here is some more reading on twist and the .223 round in general
it also has a twist to gr guide on there.

223 Rem + 223 AI Cartridge Guide

Thats a good find..
Now I just need to figure out what twist is on the barrel of my new truck gun. I bought from a guy that needed money so I have no Idea. Wonder if I tore it down if it'll be stamped on the barrel. I do know it will shoot 55 grain out to 100 really good. Im just not sure about SS109 62 grain and haven't tried any in it yet.

 

[M. Sage]

Thats a good find..
Now I just need to figure out what twist is on the barrel of my new truck gun. I bought from a guy that needed money so I have no Idea. Wonder if I tore it down if it'll be stamped on the barrel. I do know it will shoot 55 grain out to 100 really good. Im just not sure about SS109 62 grain and haven't tried any in it yet.

Should be stamped on the barrel near the gas block.

 

[M. Sage]

here is some more reading on twist and the .223 round in general
it also has a twist to gr guide on there.

223 Rem + 223 AI Cartridge Guide

Excellent article!