Friends-

I would like to have built for me an AR-15. I am pretty ignorant regarding this rifle platform, as I am a bolt action guy. Thusfar, I have acquired a stripped lower receiver. I am waiting in the wings for other parts to become available. I know I may have to wait on some of the other components. In the interim I want to go ahead and order a barrel from Krieger and hold a spot in their production leadtime. I do want to go with a 5.56 mm a/k/a .223 but, I know there is a wide variety of bullet weights and rates of twist for barrels.

Here's is where I need some guidance. What is the "Standard" Mil-surp round, in terms of bullet weight and what is the recommended rate of twist for a barrel. I know that folks are using a tighter twist for heavier bullets, but, that's about all I know.

Any and all help would be appreciated.

Thanks,

Mark

Depends their is a lot of m855 around 55grfmj also a lot of ss109 around 62gr steelcore.

The early M16 and ARs were 1x14 55gr or lighter

Seems to me the standard twist is becoming 1 in 7 I would chamber it so it can shoot both 5.56 and 223

I shoot a 1x7 in a savage bolt gun and it shoots 52gr matchkings will under .5 I have shot several groups with that load at 300 that go under 1.5 inchs

1x9 could be a good compromise as long as you stayed away from the real heavey stuff 75grs and above.

if you know it's going to be a varmint gun, I'd go 1:9 twist. That will stabilize everything up to and including the Hornady 75 gr BTHP. If you want to shoot bigger bullets, go 1:7. That will handle everything except the 90 grain bullets Sierra and Berger make, but those are only used at (relatively for the .223) extreme range shooting.

It's a common misconception that you need to match bullet weight and barrel twist rate for accuracy. This is dead nuts wrong. You just need a fast enough twist rate to stabilize the bullet and a slow enough twist rate not to blow them up. But most varmint bullets will do fine in a faster twist. The only exceptions are the more frangible bullets like the Sierra Blitz, the Hornady SPSX, stuff made for the Hornet, et cet.

So decide what the heaviest bullet is that you want to be able to shoot from the gun and select a twist based on this.

For a chamber, get a 5.56 or Wylde chamber. 5.56 NATO ammo is loaded to a much higher pressure than commercial .223 stuff. (62,000 v. 55,000 psi, IIRC). You don't want to shoot 5.56 in a .223 chamber.

After that go to ar15.com for all you care to know and then some on AR15s.

LWD

Mark,

The Krieger bbl selection tells us you are prioritizing accuracy. That also means you're not prioritizing sustained fire erosion resistance (chrome-lined), nor are you prioritizing ability to safely digest much milsurp M855.

I would select a twist rate based on intended bullet weight range. About the only reason we need 1:7 is to stabilize M-856 tracer - which would not, logically, be of interest to you.

1:8 handles just about anything else that need be done, if heavies are on your menu. But there is nothing wrong with ordering a 1:12 twist if you intend to use 50-60 grain heads.

Do order a .223 chamber if accuracy is foremost. Just don't plan on using stuff like M-855, or even M-193 (often just about as hot). 5.56 and .223 throat dimensions differ so as to make use of milspec 5.56 ammo in .223 chambers unwise. Consult with SAAMI's website if you wish confirmation.

The RRA Wylde chamber is something of a hybrid (there are others) that would allow you to safely use M-855. There are no free lunches. I'm not sure why I would want to de-prioritize accuracy in what purports to be an accuracy-first rig. But it's your call.

Sam

quote:

You don't want to shoot .223 in a 5.56 chamber

Just the opposite I thought.

http://forums.accuratereloadin...2105729/m/3281091581

The only change I've come to recently is I now think you're best off buying a chrome-moly barrel (krieger is great as are others) and have it melonited. The commercial term is QPQ or quench/polish/quench.

It is a nitrocarburizing process that makes the barrel virtually corrosion resistant (10x better than most stainless alloys) inside and out. Hard as woodpecker lips, too. Cleaning time goes down and the surface is soo hard there is substantially less chance of damaging the bore by accident. Also very slick. I did my 300 Weatherby and th eresults are spectacular and somewhat pleasing to the eye. It should add about $100 to your barrel cost. which is almost what you save anyway by switching to regular barrel steel from stainless.

quote:

Originally posted by p dog shooter:

quote:

You don't want to shoot .223 in a 5.56 chamber

Just the opposite I thought.

http://forums.accuratereloadin...2105729/m/3281091581

My thoughts also

Yes it is in the case of heavy bullet 5.56.

The modern 5.56 penetrators are not good in 223 AR as the 223 is set up for lighter softer bullets and the leade is different.

The Federal/LC design 5.56 (55gr FMJ lead core) will work almost all the time in a 223 AR except the lighter hammer spring will cause occassional misfires (about 10% IME) with the harder milspec primers.(speced for a SAW not an AR)

223s in a 5.56 AR are no issue except the twist is usually wrong for the lighter bullets.

Light bullet results in a 5.56 AR.
L to R 55gr, 50gr, 60gr


Own both, shoot both:

5.56 & 223

quote:

Originally posted by ted thorn:

quote:

Originally posted by p dog shooter:

quote:

You don't want to shoot .223 in a 5.56 chamber

Just the opposite I thought.

http://forums.accuratereloadin...2105729/m/3281091581

My thoughts also

My bad. Don't shoot the 5.56 in the .223 chamber. I'll fix the original post.

LWD

Actually, you are still incorrect. SOME 5.56 ammo is okay in 223s. In a 700/Tikka/Savage etc. bolt action you will never have a problem. In some ARs (like my R15) that have light hammer springs for a decent trigger pull you will have occassional misfires due to hard primers. Just stick with the 55gr lead core FMJ 5.56 as made at LC under the Federal contract (brown 20 round boxes).

In this day and time, I would want an AR barreled with at least a 1 in 8 twist, and be chambered to shoot any 223/5.56mm ammo.