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Discussion Starter #1 (Edited)
Now that I have the beginnings of my very first AR I have been trying to find out what length barrel and with what twist rate is optimal for shooting the widest variety of bullet weights with the best accuracy.

A gunsmith friend of mine in Ca. says 'just go with a 1:9 twist rate and that will do just fine. 1:7 twist rate barrels tend to burn out faster'.

Other research states that a 20" barrel provides higher velocity, but there isn't much difference in accuracy if using a 16" barrel. At 500 yards both barrels will hit a man size target and the 20" will give a little bit better grouping. Obviously, this makes sense for longer distances since the 20" barrel has that little bit longer distance from the front to rear sight. Apparently though, the accuracy isn't so greatly improved to be much of an issue.

Other research I have done comes up with a 1:9 twist barrel not stabilizing higher weight bullets in flight though it's great for 55g bullets.

Then there's the question of the metal used for the construction of the barrel since there are a plethora of different choices as there is with types of barrels, fluted, pencil M4, heavy etc. - so, which barrel is going to have the longest life/be the strongest and take any .223 bullet weight happily and do a great job of getting the bullet to the target?

This may be the only AR I ever get to build so I want to make the best possible choices with building the upper. This will be a 'for anything AR'. It has to be.

All advice is very much appreciated.

Thanks everyone,
Will
 

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WHSmithIV:

Your choices are highly dependent on what you want to do with the gun. You do have several choice: Varmint, Target shooting, plinking, hunting. Each probably has an ideal set up. Are you planning to mount a high power scope or a military type sight or a common red dot or go with metal sights?

55gr bullets work best in the slower twist barrels like 1 in 9. Heavy bullets (in the 70 gr class) work best in the 1 in 7. The 1 in 8 is a compromise but my 1 in 8 likes the heavy bullets better than the lighter bullets.

First you need to determine your usage. Then, whether you want to shoot the light bullets or heavy bullets.

Gas impingement operation or short stroke gas operation is also a choice. The shorter barrel guns seem to like the short stroke gas operation. But any of these guns with short barrels are a bit less reliable in operation than the longer barreled guns. It has to the variability of the gas pressures in the short barrel gas port location being so close to the cartridge generating the gas. If you don't need the compactness of the 16 inch barrel then go with a longer barrel.

My varmint AR uses a flat top receiver, with a aluminum floating hand guard, a rigid stock, and a 24 inch Lothar Walther barrel. It has a high power scope too. This is a Varmint or Target setup. It shoots tiny groups. I built it myself with a match trigger and a set of common lower and upper internal parts. It is gas impingement operated. I also have a TacSol 22LR conversion Upper for it that is extremely accurate (recoil operated).

I also built an AR type gun with a 50DTC (50BMG cases reworked to get around the California ban on 50 BMG guns) bolt style conversion upper and a fixed stock. It has no magazine and is single shot feed manually. It has a 6-24 power tactical scope on it and we shoot it at very long ranges.

These AR's are a versatile platform on which to build a gun for almost any kind of shooting you might like to do. You decide.

Exactly what do you want?

LDBennett
 

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We hunt with ARs almost exclusively; all because the short 16 inch barrel and collapsible stock. You don't end up almost getting knocked off the 4 wheeler on narrow trails; those trees will reach out and grab ya. That 10 round magazine is great when ya miss too. I find myself taking shots on the fly and getting lucky more times than not.

So what's the application? If I was shooting targets, I'd have a long barrel, for hunting, short. I also like the 6.8 caliber hands down over the .556. We have killed all kinds of caribou, over 10-12 blk bear, and a few wolves with that 6.8 spc Stag

Truth be told, my .556 Ars haven't been outta the safe in a couple years, the 6.8, 338, and 308s never make it into the safe. I'd really consider a different upper, so many new calibers available.
 

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Discussion Starter #4
Well, I'm going with carry handle, iron sights and a flip up red/green dot sight. The most likely use will be taking out a wolf or a mountain lion when up in the passes or for them being down here attacking the sheep. Thing is, all the mags I have are in 5.56 - seems counter productive to try to sell them all and change them to something else. I had originally thought 6.8 myself but then ended up with 5 Pmags and a couple Israeli mags.
 

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From reading your past posts, and from where you describe the area you live in, for barrel length I'd say go with an M4 length barrel. That's not saying an M4 barrel, because those are milled for the grenade launcher, and I doubt if you want that. Not that it makes all that much difference, but to me that milled portion has to have an effect on accuracy. That difference may be ever so slight that you may never notice it, but if you are building the rifle yourself, why not give yourself a little 'edge'?

On twist rate, if I were building a rifle that I'd want as a survival tool, I'd go with a rifle that ammo would be the easiest to get. There are oodles and gobs of 55 grain FMJ .223/5.56, and worst case scenario that would be more likely available than the heavier bullets. The heavier bullets may have an edge on range, but if they are not available that would'nt do you much good.

I like your plan on getting the carry handle. Again, that rifle looks like it may be a survival tool, and in my humble opinion you are better served by that setup. You can always get optics and play with them, but a solid sight system won't let you down or run out of batteries.
 

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Discussion Starter #6
Thanks for that Jim,
I didn't realize that heavier bullet ammo could be harder to get than the 55 grain stuff. I'm just going to use a simple flat top upper receiver so I can use a removable carry handle with the extra flip up sight. Same with the gas block - flat top gas block and add the front sight. This I figure is the most versatile since what's on those rails can be removed and changed.

I'm going to go with a hand guard that has rails also - again it's a matter of versatility and I am likely to add a light to the rifle at some point for those dark winter nights.
 

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Now that I have the beginnings of my very first AR I have been trying to find out what length barrel and with what twist rate is optimal for shooting the widest variety of bullet weights with the best accuracy.

A gunsmith friend of mine in Ca. says 'just go with a 1:9 twist rate and that will do just fine. 1:7 twist rate barrels tend to burn out faster'.

Other research states that a 20" barrel provides higher velocity, but there isn't much difference in accuracy if using a 16" barrel. At 500 yards both barrels will hit a man size target and the 20" will give a little bit better grouping. Obviously, this makes sense for longer distances since the 20" barrel has that little bit longer distance from the front to rear sight. Apparently though, the accuracy isn't so greatly improved to be much of an issue.

Other research I have done comes up with a 1:9 twist barrel not stabilizing higher weight bullets in flight though it's great for 55g bullets.

Then there's the question of the metal used for the construction of the barrel since there are a plethora of different choices as there is with types of barrels, fluted, pencil M4, heavy etc. - so, which barrel is going to have the longest life/be the strongest and take any .223 bullet weight happily and do a great job of getting the bullet to the target?

This may be the only AR I ever get to build so I want to make the best possible choices with building the upper. This will be a 'for anything AR'. It has to be.

All advice is very much appreciated.

Thanks everyone,
Will
That is the great thing about the ARs. You can dress 'em up and then change them as the objective changes. Kinda like Barbie Dolls for men.

I don't know if anyone has mentioned this or not but there seems to be some debate over direct impingement systems VS a piston system.

I personally don't know enough about it to argue it either way. The two ARs I own both use DI and I have had no issues with them but I am a clean freak when it comes to firearms. Shoot it once, break it down and clean it. I love the smell of Rem Oil in the evening. As I understand it DI systems require a bit more cleaning than a piston system to remain reliable but I could be wrong about that.

Sig makes a great forend grip light. Has a laser sight and a 175 lumen ( I think ) flashlight with a strobe function. The light is either constant on or momentary in either mode. The grip part is a little big because it houses the 4 AA batteries that power it. I like mine but it is pricey.

Mine is a survival weapon and my weapon of choice for Home defense. I use a 16 inch 1 in 7 6 groove barrel. I use an F marked front sight and a Magpul rear flip up iron sight. A also have a Barska 3-9X40 scope and a barrel mounted bi-pod. Mostly the scope and the bi-pod stay in the case, but I have them if I need them. Nearly all of my ammo is 5.56x45 55gr FMJ. I do have a few boxes of .223 55gr FMJs as well and I have about 20 tracer rounds. I got them when I got the Slidefire stock. They are a hoot to shoot.

With the iron sights from a standing position I can make a 6 inch 30 round group from 40 yards. That is enough for me. I don't have to be able to circumcise a gnat at 1,000 yards. ( Not with the Slidefire in the slide position, NO ONE is that good. )

If this is a survival weapon I also highly advise getting a Magpul mag link. At least one but two or three would be better. There are a lot of mag links out there but pay the extra bucks for the Magpul, it is more than worth it.

Of course all of this is just my opinion and is no more valid than that.
 

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The heavier bullets are NOW harder to get than the 55 grain FMJs. The 55 grainers have been around for a long time, and it seems that everyone and their cousin produces them. Now that the current standard issue seems to be the 62 grain FMJ, those MAY get easier to find. It's a hard call.

One thing to consider is that after our Government winds down foriegn operations, there MAY be a glut of the heavier 5.56mm ammunition on the market eventually. That is, of course, based on an assumption that the Government will have a kinder view of releasing surplus ammunition in the future than it currently holds.

My ARs are an old (in years) Colt SP1 and a newer Bushmaster M4 with the carry handle on an A3 flat top receiver. I don't have any intentions of mounting other sights or accessories on either. Everyone has different needs, and the AR is a great platform for just that.
 

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Discussion Starter #9
So, back to the twist rates siplace and Jim..
What I was told was that the 1:9 twist rate doesn't stabilize the heavier bullets enough which is why the military went with 1:7.

That being the case (if it's fact) leads me to the question as to how the lighter 55 grain bullets perform with the 1:7 twist rate?

This also leads to the next questions on barrels. Do I want the barrel chrome lined or not? What was the purpose for chrome lining barrels anyway?
 

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Will. .224" 1:9 will do anything up to about 69 grain at .223 velocities, heavier needs faster. 1:7 is ideal for 70 gr plus.
The barrel burn out factor between 1:7 and 1:9 is measured in the hundreds of rounds. which isn't likely to youll notice given an accurate barrel life of over 10K for either one.

My advice to you for a .223 AR is 16-20" barrel, H-BAR contour, with float tube. Select the twist rate you want and roll with it.
 

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I'm starting to get in over my head here. As far as to the 'why' on those chrome bores, I have not read any tech information from the builders on that one. I can only go back to the 1960s and early 1970s when the AR rifles were first issued without cleaning gear - "They are self-cleaning" was the first thing told to the troops. Being used in a tropical enviornment, as a soldier I heard that and ASSUMED that the idea was to keep the bore from rusting in our hot/damp enviornment after firing.

That is the pitiful sum of my concept as to the 'why' of those chrome bores.

The faster twist rate (1 in 7") is supposed to better stabilize the heavier (62 grain) bullets, and it seems that this idea is correct. It is also my understanding that lighter bullets can blow-up in flight if spun at the faster rates. I've never had it happen, nor have I personally seen it, but from time-to-time I've read reports that this is so.

(Josh answered while I was fat-fingering my note - and his is sound advice as always. I'd agree on the 20" barrel if you are going to do a bunch of long range shooting. For me, a shorter carbine length barrel works because -for me- I'd tend to always have the rifle with me, but that might not always be the case if the rifle were not quite as handy with a longer barrel. Just my two pennies on that one.)
 

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Chrome is a hard wearing surface. Plus its corrosion resistant. Its been proven to increase the service life of a rifles bore substantially.

The 7 twist was adopted for the M4 and CAR15s running 11.5" barrels shooting the then new 62 gr steel core penetrator rounds. The reduced barrel length reduced the velocity which dropped the required RPM the bullet needs to be stable. 7 twist is a fantastic twist rate but you need to run heavy .224 bullets to realize the best accuracy. The bullets spinning apart is mostly a problem of decades past. Bullet metallurgy has advanced to a point that just about all projectiles are stable at any perceivable RPM a bore twist/cartridge combination can put on them. .22-250 thru a 7 twist.. Thats a S***load of RPM and in 1975 would shred any bullet lighter than 80 grains. But today even the 36 gr varmint grenades are built to handle excessive RPM without disintegrating.
 

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Discussion Starter #13
Thanks JLA,
Given the current situation with finding parts at reasonable prices, the actual price I'll have to pay determines pretty much what I will buy. I WILL build this rifle for a grand total of under $700 - I'm going to try to build it for under $600. Parts are starting to show up at original fair market prices but I've been calculating all the rest of the parts also and determining if they are available at fair prices or overblown still. I am trying to buy most parts from on-line auctions because they will ship as fast as I send the payment. The guy I bought the lower receiver from with the DPMS lower parts kit had a 'buy it now' price of $250. He was a bit depressed when I won the auction at $167.77

So, with the shipping it was $190.77 plus the $20 transfer fee my FFL charges - retail the MAG Tactical Systems lower receiver MSRP for about 160.. DPMS LPK for 60 before the panic crap. So, I bought it at fair market value - before the panic.

I'll start putting the lower together this week AND post pictures :)

One very good thing about the AR and AK platforms is that only the lower receiver has to go through an FFL. Everything else ships to your door. For me, this is important because I can not buy parts here. The nearest places with parts are over an hour drive to get there. Lots of gas at close to 4 bucks a gallon. If I have to go to Idaho Falls or Blackfoot it's $40 in gasoline round trip in our pickup - our only vehicle. It's MUCH cheaper to have items sent to our door and pay the shipping. The local post office is only a mile away - I can go on horseback if I want to.

I have no problem with building it myself. If I have to assemble the upper from scratch then I do have to buy a vice block. I already found an armorers wrench for $15 and ordered it. I already have a vice so that doesn't count. AR upper vice block I can get for $24.

I still don't know about the chrome lined vs. not chrome lined barrels. Since 1:7 twist rate happily will handle 55 grain bullets and not burn out with the lifetime of the rifle and the amount of ammo I ever expect to put through it - that's fine. Basically, I'll take what I can find then.

Thanks Josh,
Will
 

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Discussion Starter #15
ejkoechling - that doesn't help - at $239 for a barrel only that blows the budget for the rifle. I already know where I can get 16" barrels for $119 in stock now.

I would really like to know though what the difference is between a chrome lined and a non chrome lined barrel.
 

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The following is from the owner of ArmaLite, interesting explaination as to how we ended up with the 1:7 twist.



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Below is information from the owner, Ret. Lt. Col. Mark Westrom on the subject.

The Facts Behind the 1:7 inch twist AR barrel

There's a lot of buzz around that the 7 inch twist barrel is just the thing for the AR family and that a 1:9 inch twist barrel is second rate.

This isn't actually true, and ArmaLite's President, Mark Westrom, was deeply involved with the matter while a Civil Servant at the Armament Command at Rock Island. It's an interesting story.

In the early days of the M16A2 he received a message that Procurement was set to buy 155,000 M16A1 barrels just when the Army was switching to 1:7 inch M16A2 barrels. The problem wasn't merely poor accuracy or logistics; he was concerned that because the 1:12 inch twist barrels wouldn't stabilize the M855 well enough to prevent wounds that were likely to raise Geneva Convention complaints, it would make both legal and logistic sense to settle for a compromise barrel that would handle both.

He consulted with Col. (Dr.) Marty Fackler, he of the Army's Wound Ballistics Laboratory, who agreed with him and offered to run some pig cadaver tests to verify if a problem existed. Westrom sent the proper request and Fackler confirmed that use of the M855/865 bullets in the 1:12 inch twist left dramatic but somewhat less than effective wounds.

Westrom consulted with ammunition specialists at Picatinny Arsenal and proposed that even though 1:7 was required "to stabilize the M856 tracer" the 1:9 inch twist rate should be fine for both M193 and M855 ball rounds and would be good enough for the usual purposes of tracers: close in fire at night. He was surprised when he was told "No, 1:9 is actually pretty much optimal for the M856 tracer. 8.5" twist actually."

Upon further questioning he was told that 1:7 was used in the M16A2 because it was used in the M249 Squad Automatic Weapon. FN submitted the M249 with 1:7 inch twist and it won the SAW competition and was thus produced with that barrel. They didn't know why 1:7 was used in the M249. (It over stabilized those bullets, which led to decreased long- range accuracy and reduced barrel life.)

Westrom asked the authorities to call FN to find out why they used the odd 1:7 inch rate.

The next day Picatinny called back and said "You aren't going to believe this: FN remembered the accusations the US received over the cruelty of the early 1:14 inch rifling twist of the early M16." They used 1:7 inch twist so they'd never have to answer that complaint.

In other words, the 1:7 inch rifling twist was a political decision of a Belgian civilian, not a technical decision at all. As one foot follows the other, we've gone forward with the odd barrel.

So here's where we are today. 1:9 is great for M193 bullets and to around 70 grains. 8 inch twist is fine for bullets up to around 77 grains. Higher twist rates are sometimes used for even heavier bullets.

But these bullets aren't those used outside competitive shooting, and normally loaded one shot at a time. Some military ammunition uses a 77 brain bullet, but that's rare with commercial arms and is VERY hard on the bolt of the M16.

ArmaLite does make rifles with 1:7 inch twist for those contracts that require it, but for almost all military, police, and civilian use it's suboptimal.

Our customers learned this early on. Years ago ArmaLite sold 1:7 inch twist barrels and the market very much disliked them. It took a long time to sell them. The idea of a chrome-lined 1:7 inch barrel for match-type isn't very logical, but we'll build them when the customer demands.

The bottom line is though, that sometimes what the customer wants is driven by funny advertisements rather than technical facts. This isn't the only issue that falls into that area.

Westrom's idea is that DOD should switch to the 1:9 inch barrel for both the a1 and A2 rifles? He was allowed to convene a meeting on the topic that stunned him. He was savaged for the idea. And this was by friends. He raises the issue later when another 120,000 1:12 inch barrels were being bought, to the same end.

But one of his first actions at ArmaLite was to standardize the flexible 1:9 inch rate.
 

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I thought it might be a budget buster at that price. The reason I sent it is if you go to the link ed page, scroll down an they give a brief explanation of the chromed bore and chamber, and some other brief explanations of the barrel. Thought you might find the info interesting at the least.

Chrome Bore and Chamber
One of the first modifications that were made to the original M16 in the mid 1960’s was the addition of the chrome lined bore and chamber. It is now a world wide standard in the industry for a battle rifle. The chrome bore and chamber is harder than the barrel steel and on the USGI M16/M4 rifles will aid in chambering, extraction, and reliability. It increases velocity, and also resist against fouling and corrosion from extended use in the field. This gives the end user a longer barrel life with less required time in maintenance and cleaning.

Hope you find it helpful.
 

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Alot of good info guys...
 

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Discussion Starter #20
All you guys, thanks very much. That article GunHugger was REALLY interesting. I have the feeling we are all learning from this thread.

So, now I know I will stay away from 1:7 twist rate barrels and try to get a chrome lined one. I will stick with a 16" barrel as being my optimal. Saving those 4" may be quite beneficial since I'll be carrying this rifle on horseback always when I go to the mountains (a whole mile from our home). I'm still fiddling with the idea of going down to a 14.5" barrel. I can get a spot weld put on the bottom of a flash hider or compensator easy enough to bring the barrel length to 16.x" total.

I'll keep diligently searching for parts.
 
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