Ok, I cancelled my order with Bushmaster for a 1/9 Twist Gov't profile upper as I didn't feel like waiting 8 weeks. I'm going to be palcing a new order for a gov't profile upper elsewhere and I've came across a choice between a 1/9 and 1/7 twist barrel. It would take a few weeks to get the 1/7 twist while I can get a 1/9 barrel immediately. I've been doing a search of this board and it seems that the only difference is the 1/7 twist can fire those heavier tracer rounds. Granted Im never going to be shooting tracer rounds from my AR, but I figured if I'm already getting a gov't profile barrel I might as well be 100% authentic and stick with the 1/7 twist.

Any thoughts?

Quoted: Ok, I cancelled my order with Bushmaster for a 1/9 Twist Gov't profile upper as I didn't feel like waiting 8 weeks. I'm going to be palcing a new order for a gov't profile upper elsewhere and I've came across a choice between a 1/9 and 1/7 twist barrel. It would take a few weeks to get the 1/7 twist while I can get a 1/9 barrel immediately. I've been doing a search of this board and it seems that the only difference is the 1/7 twist can fire those heavier tracer rounds. Granted Im never going to be shooting tracer rounds from my AR, but I figured if I'm already getting a gov't profile barrel I might as well be 100% authentic and stick with the 1/7 twist. Any thoughts?

1:7 is the best all-around twist-rate, unless you intend to shoot bullets lighter than 55gr.

What Dave said. Its nice to know that you can stuff some 69 or 77gr bullets in there and go to town, and still shoot 55gr for practice.

.

So even with shooting 55 grain, you would go for a 1:7? Isn't that the reason why they switched to shooting 1:9?

Sammy

Quoted: So even with shooting 55 grain, you would go for a 1:7? Isn't that the reason why they switched to shooting 1:9? Sammy

No. 1/9 was picked when heavy bullets were rare. 1/9 is so you can use 40/45 gr varmint bullets.

55gr works just fine in 1/7.

Thanx Combat_Jack.

Sammy

Quoted: Quoted: So even with shooting 55 grain, you would go for a 1:7? Isn't that the reason why they switched to shooting 1:9? Sammy No. 1/9 was picked when heavy bullets were rare. 1/9 is so you can use 40/45 gr varmint bullets. 55gr works just fine in 1/7.

45, 50, 55, and 62 grain, twist just fine in a 1/9.  I find that 55 grainers are just as accurate (MOA) in my BM 1/9 as my Colt 1/7.  Unless your going to be doing a lot of match shooting with 69 grain match kings or a bigger grain bullet, you'll be happy with with a 1/9.

55's shoot great in my 1:7 and on the flip side of the coin 69gr SMK's are the most accurate round in my 1:9 Bushy Varminter, sub 1/2" 5 shot groups at 100yrds

Personally, I'd go w/ 1:7 for M4 Profile and 1:9 for 24" unless you'll be shooting heavier then 69gr's. In that case 1:7 regardless of barrel length.

Quoted: 69gr SMK's are the most accurate round in my 1:9 Bushy Varminter, sub 1/2" 5 shot groups at 100yrds

I'm going to have to try 69 gr SMK's in my 1/9!

Quoted: I'm going to have to try 69 gr SMK's in my 1/9!

Here's the load info

Temp: 50F
Alt: 60ft
69gr SMK
CCI primers
2.260 OAL
24.5gr Vargat
@ 100 yards I was shooting sub 1/2" 5 shot groups
Couldn't use the chronograph do to rain so no Velocity info to report :(

Disclaimer: Safe in my gun doesn't mean safe in your gun, start low and work up to this load.

I've not had any problems with 69 gr bullets out of my 1/9 bm 16" hbar.  They shoot very well, as a matter of fact the best 5 shot string I've ever shot was 69 gr stuff.  Granted I was using a bench rest to zero it in, but that stuff was the shit.  I have a difficult time finding the heavier stuff anyway.  I'll get a 1/7 one day, when the heavy stuff is more available.  It is my opinion that you won't go wrong either way.  Chances are you'll end up having more than one Ar anyway.

btw if your going to be 100% authentic don't forget the 3rd spot on your selector.

Unless you intend to shoot bullets at the extreme ends of the weight spectrum (lightweight 40gr varmint bullets vs 77gr OTMs) the construction of your barrel is far more important than the rate of twist.

-4150 steel
-Chrome-lined bore and chamber for extended barrel life and ease of cleaning
-Forged FSB

From a standpoint of practical accuracy, with 55gr bullets I can't tell the difference between my 1/9 and 1/7ROT barrels. My SHTF weapons are 1/7ROT only because 75gr Hornady TAP is my zombie slaying ammunition of choice. That being said I would wager that 75gr TAP would be sufficiently accurate at typical defensive shooting distances even in a 1/9ROT barrel.

Some of us even have 1/12...

1/7 here. 55 grainers work good. I bought some Wolff cuz it cheap to shoot steel with, and had no problems hitting the 300m target with irons.

1/7 is FINE for 55 grainers.

Just curious; has anyone here actually shot any of the 40 gr. pills in a 1:7 twist?  I've heard that they would spin apart. I only have a 1:9 twist right now, but was thinking of going to 1:7 or 1:8 in a 16" bbl. later.   btw a coworker has the RRA Varminter with a 1:12 and loves the 40 gr. BT; he's getting .3 moa with it.

Quoted: Just curious; has anyone here actually shot any of the 40 gr. pills in a 1:7 twist?  I've heard that they would spin apart. I only have a 1:9 twist right now, but was thinking of going to 1:7 or 1:8 in a 16" bbl. later.   btw a coworker has the RRA Varminter with a 1:12 and loves the 40 gr. BT; he's getting .3 moa with it.

I'm a reloader, and a while back I tried some 40gr Nosler Ballistic Tips in my 1/7ROT Colt 6601 HBARs. I loaded them primarily to see what would happen, since one of my range buddies assured me that they would break apart in flight, or disintegrate in the barrel, cause the sky to fall, or make me sterile.

I'm happy to report that aside from subpar accuracy (from over-stabilization perhaps??) nothing catastrophic happened. It should be noted that I didn't spend any time "developing" this particular handload. I grabbed the COL, powder charge etc right out of my trusty reloading manual. Had I taken the time to develop the load properly it's probable that my results would have been better.

I don't know if Nosler Ballistic Tips are more/less durable than other lightweight varmint bullets, but they most certainly held together when used in my 1/7ROT barrels. Perhaps Brou or someone else with more authority than I have on bullet construction could weigh in on this.

i just shot black hills 75gr out of my 1x9 chromelined barrel 16" m4 gov. profile and was making nice center mass hits @ 200m...  no signs of key holding at all...

i want to get my hands on some 77gr rounds and see what i can do with it... i'll get another box of 75gr and shoot 300m with it and see what happends...  steve @ ADCO had a forum that i can't find that talked about him shooting at 600m with a 16" 1x9 barrel 77gr......

the main negitive is that a 1x7 twist is faster so your barrel life will be less....  and that you really can't shoot anything under 55gr... and there are some who do still have problems with 55gr...  i almost only shoot 55gr so i wanted to make sure my twist was perfect for that round...  i also love to shoot 45gr HP's are varmits... and i wouldn't be able to do that with 1x7 most likely

i think the same way that 1x7's can shoot 55gr's and lower, is the same as a  1x9 can  shoot 75gr and higher...  it'll shoot it but maybe  not as good as it can...

if i was making an SPR where i was almost always going to be firing match heavy ammo out of it... 1x8, 1x7.7 or 1x7 would be my choices... 1x8 pref.

both twists are fine... its not that big of a deal

the main negitive is that a 1x7 twist is faster so your barrel life will be less....

Jar3ds, I've heard this too but haven't found much discussion about it. It makes sense to me for the reason you mentioned, but I'd love to learn more. Do you know of a resource somewhere that talks more about it?

My thirst for information is never satiated

The miltary uses the 1:7 twist. It would be good to ask a military armorer about the barrel life expectancy of a 1:7. The military puts many rounds through these guns. I am sure the barrel life is just fine.

the main negitive is that a 1x7 twist is faster so your barrel life will be less....


the above statement is true. A spining object gets the angular mementum. As the bullet leaves the barrel, the barrel rifling lines provide the bullet's angular mementum. With faster twist, the rifling lines worn out faster. Therefore, your barrel life gets shortened. Actually, bullet mass is the other factor to shorten your barrel life. The heavier bullet also wears out the barrel faster.

If you just shoot <62 gr bullets, IMHO 1/9 is the best if you consider the accuracy as well as the barrel life. 1/7 is simply too much.

Military uses 1/7 because of the tracer bullets. This is the only reason.

Quoted: The miltary uses the 1:7 twist. It would be good to ask a military armorer about the barrel life expectancy of a 1:7. The military puts many rounds through these guns. I am sure the barrel life is just fine.

A military barrel that is frequently fired fullauto in an M16 or M4 isn't going to wear the same way as a barrel in one of our semiauto ARs. My oldest Colt has 15k+ rounds through it since I bought it new in 1991. From a practical shooting standpoint I can't perceive any measureable difference in accuracy-but that doesn't mean there isn't one.

I'd simply like to know if there is a scientific way to measure or compare friction/wear etc from one versus the other. I'm not sweating it either way, but I'd like to know for informational purposes.

Shorter barrel life and the 55 gr bullets don't work well? Bah, humbug!!!

Ask KevinB, he has some 1/7 twist barrels with over 25k rounds through them and still going strong.  I've got over 8000 rounds through my 1/7 and it's still just accurate as it was when I first got it.

While I have no doubt the 1/7 will wear out sooner than the the 1/9 I believe that unless you are a benchrest shooter who needs to maintain that .25 MOA accuracy the difference in the wear and tear between the two are negligible.

How many 1/7 owners on this site have worn out their barrel?  It's more likely you'll want to buy a new rifle or carbine before you wear it out...

As far as the 55gr not working, I don't think there's one person here who has a 1/7 that has trouble with any 55 grain ammo worth shooting.  In fact I've seen quite a few here who have experimented with bullets all the way down to 40gr and have no problems with them.  The 1/7 twist is really more versatile than most people give it credit for.  

As for me I'll gladly give up the ability to shoot ammo 40gr and below to be able to shoot the better heavier rounds.  

Barrel throats will give out way sooner than the rifling, especially if you are shooting a bunch of 75/77 grain stuff loaded hell for stout.  When the throat goes, accuracy goes with it.  But the barrel rifling will remain fine down stream of the throat.

Good point.