I'm building up a 16" carbine and I'm trying to decide on which barrel to use.

I am still torn between Stainless or Chrome lined, but before I make that choice, I want to take twist rate into account.

I think it's pretty much the accepted logic that 1 in 9 is a good all-around twist rate for typical ammo.  

I've seen some 1 in 8 and 1 in 7 barrels though that are making me second-guess myself.

I know that the faster twist is necessary to stabilize longer, heavier bullets.  I guess my question is, what makes longer, heavier bullets better than lighter faster bullets?  

Also, considering the outside chance of a SHTF situation where heavier rounds aren't available, is it at all advantageous to fire the typical 55 to 62 grain projectiles through such a fast twist?

Let's hear your ideas on why 1 in 9, one in 7 or any other twist rate is better than the others.

Thanks

Have you read the [url]ammo-oracle.com[/url]?

A chrome lined barrel should outlast a stainless barrel.  The stainless barrel [i]might[/i] be more accurate.  If you're going to do a lot of rapid fire you're probably better off with a chrome lined since it'll take the heat better.  Especially if you get one in 4150 steel from BM or Colt (vs the 4140 steel used by Armalite or RRA).

1/9 has been considered the "all around" twist until very recently when the 75/77gr rounds became popular.  They're fine up to 69gr and I think the 72/73gr match bullets are OK.  75/77gr is a crap shoot in a 1/9.  Many people say it works in theirs, but just as many say it won't.  I've shot 75gr Black Hills blue box in two different 1/9 20" BM barrels and had poor accuracy with both (3" groups at 100yds vs. 1" groups with the blue box 52s & 69s).

The longer/heavier bullets tend to fragment in tissue at lower speeds, so they're above "frag speed" to longer ranges.  They also tend to hold on to velocity better at longer ranges, which is why the match shooters use them.  The military is using them because the shorter barrel on the M4 reduces the M855 velocity so much it drops below frag speed within 50m.  The 75/77gr gets that range back up a bit.

So do a little research in the Ammo forum and decide whether 69-73gr is heavy enough for you, or if you want to be able to shoot the 75/77s.  The 55/62gr will shoot just fine in the faster twist, so I'd consider 1/7 the new "all around" twist.  (Some people will claim they'll shoot worse, but 99.9% of shooters can't shoot well enough to tell.  I can't.)

Personally, I won't buy any new barrels with slower than 1/8 twist because I don't want to limit my options...but I'm not going to go out and replace my 1/9 anytime soon either.  

That is perfectly acceptable accuracy for a defensive carbine.  

I suppose it is, but it's also twice the group size of M193 at that range.

Has anyone ever got an answer from RRA or ARMALITE why they wont use 5150 ?It seams a shame to let COLT and BUSHMASTER corner the market .

DPMS has a couple barrels in 4150.  I would hate to pay $.60 a round and get 3MOA accuracy when all I had to do was get a 1/7 twist and get 1MOA accuracy and sacrifce about .1 MOA with M193 to get it.

My advise is get a chrome lined 1/7 twist barrel.  It will do everything you could possibly want and do it well.

Because there is probably a higher profit margin using 4140 and they're having no problems selling them.

Artifex,

GO with a 1/7 16" barrel in 4150!  The 1/7 will shoot 55gr on up and is probably the best all purpose twist at this time.

I went with a CMMG/DPMS 1/7 16", 4150 with M4 extended feedramps and fully chrome lined.  So far it has been 100% reliable worked like a champ!  

The CMMG/DPMS upper does come with a cast front sight but Steve at ADCO can put a forged on on for $65.

Here's my thinking, I wanted a 1/7 barrel that was 16 inches so I didn't have to weld or pin the flash suippressor.  The little bit of extra velocity didn't hurt either.  

I felt it was better to get the CMMG 1/7 16" upper and replace the front sight than to get a Bushmaster 1/9 16" barrel with a forged front sight and not have the ability to shoot well with the better, heavier ammo.  

IMHO, the benefits of a fully chrome lined 1/7 16" barrel in 4150 were worth the extra expenditure of having to get a forged front sight.

The only other twist rate I would get would be a 1/8 for a SPR, for everythig else I would go with a 1/7.

And your point is?  You don't need quarter sized groups at 100 yards for a defensive carbine - and in a life-or-death situation you won't be shooting them.

I don't know too many people who can shoot 2" groups while the adrenaline is pumping and they are running, not to mention the fact the odds of you needing to shoot as far as 50 yards is pretty remote.  

I'm skeptical about 1 in 7 for my purposes.

I don't often shoot the heavier grain bullets, I shoot the garden-variety 45-68 grain stuff, and I need a twist that will work for a large variety of ammo - which seems to be 1 in 9.

I have used Bushy 16" barrels usually, but want to switch to a mid-length, which dictates a RRA or Armalite.  

I want stainless or chrome-lined, since this is going to be a "tactical" style carbine, reliability being paramount, that stainless barrel will probably give way to chrome lined.  

SO really, I guess my question is, between my choices, which are Armalite Chrome lined 1 in 9 or stainless 1 in 9 and RRA stainless 1 in 8
which is the best choice?

Forest:
I guess my point was that the 75s were barely stable in my 1/9 barrels.  I agree that they're accurate enough for defensive use at shorter ranges.  But while they're 3 MOA at 100yd they may not be 3MOA at longer ranges, and they could get worse as the temp drops.  


Artifex:
I think I'd go for the chrome-lined 1/9 in your case.  You might not be able to shoot the 75/77s, but you said you aren't likely to anyway.  And as Forest noted, they'd probably still be OK for the ranges you're talking about.

Plus I believe the chrome Armalites are thin under the HGs so it'll be maybe 3/4 lb lighter than if you went with either of the stainless barrels.

Mike,
I've gone to 200 yards with a 14.5" 1:9 twist and again I was getting acceptable accuracy for that range (nothing to brag about - but I could keep them on a paper plate no problem).

I do plan on repeating my tests this winter if I can find a cold enough day to go shooting on (then we'll see if 1:9 is enough in the cold).  Unfortunetly I won't be seeing any -40 degree temps so our members in AK may want to try it up their way.

Artiflex,
1:7 works fine with 55gr FMJ which is probably 99% of what you will be shooting.  I have not tried it with lighter rounds.  I have [i]*heard*[/i] of the lighter (45gr) varmint hollowpoints self destructing but I have not seen it, and it may be due to poor QC on the round...

However if you plan on lots of varmint hunting with your 'all purpose' rig then 1:9 should suffice.

In spite of the advise towards 1 in 9 I'm recieving (which I appreciate)  I'm starting to lean towards the Rock River arms 1 in 8 stainless.

I'll just adjust my ammo of choice up to 62 or 68 grain.

Since accuracy is a concern for me (hopefully, all this rifle will be doing is holding good groups on paper out to 200 yds) and the possibility of me being involved in a SHTF is relatively miniscule, chrome lining isn't really something I'm going to lose sleep over.