How about a heavy 12.5 inch 5.56 AR for accuracy?

[brunop]

OP can carry his own water, but...

I said "...it's barely moving at 600", and "FCC GMM starts out at 2340 from a 16" barrel"

he said, "I don't care: I like punching holes in paper."

Fair enough. I know guys who like silicone boobs, too (looks almost the same, not at all the same function or feel...). No judgement from me, and everybody gets to do their own thing.

 

[brunop]

resource over on AR15.com (one guy with a chrono and a lot of different load data...) has MV from both 16" and 20" barrels because of the box-labeled MV from a 24" barrel in some commercial loads. https://www.ar15.com/forums/ar-15/V...s-16-Middie-and-20-Rifle--223-5-56/16-676005/


Basic deal on various loadings of XM855 = 2965 fps. MV, and 2-3 MOA. Notable exception = IMI 2013 2-digit ammo: "very accurate for XM855."

Fed. 62gr XM855............ NATO LC 13......................16" barrel = Av. 2967 , ES 73.................20" barrel = Av. 3040 , ES 82........... "Typical Milspec 2-3 MOA"

Federal ballistics table says ~2380 fps @ 200 yards with ballistic coefficient of .307, so basically almost all .223 bullets are going to "not perform" at 200 or more - even out of a 16" barrel, whether green tip, 'match', or whatever.

 

[Firemedic8998]

"1/9" twist will outshoot any 1/7 twist with bullets under 70 gr. across the board". "I very much expect that this is not true across all bullets and all loads, so your fave ammo purchase or 'recipe' is going to figure into this question."

I should have made this more clear. When we were doing accuracy testing in the mid 90's at Bushmaster we spun up multiple barrels on 1/9 and 1/7 chrome lined blanks in the same profiles from 11.5 inches up to 20 inches, as we were pursuing a government contract at the time. In our testing which involved eliminating as many variables as possible and testing twist rates only head to head, we found in our testing that using the same ammo in the same barrel length, a 1/9 twist barrel will outshoot a 1/7 twist barrel regardless of the barrel length being tested. This testing was the primary reason Bushmaster stayed with the 1/9 rifling twist for so long.

Obviously the 77 OTM grain ammo was not available back then and the heaviest projectile we tested with was a 69gr Berger IIRC, as we knew the 1/9 would not stabilize anything heavier in a short carbine barrel. We ended up winning the Department of Energy contract with our chrome lined 1/9 twist M16A2 barrels as they were not going to be using tracers, and our submitted 1/9 barrels won the accuracy competition portion of the testing by a substantial margin over the 1/7 barrels being fielded by the other competing manufacturers. So there's that factual information and it can be researched and verified if anyone's interested. I don't recall the GSE contract number but it was one of the few U.S. government contracts that Bushmaster ever actually won, and it was for the DOE nuclear material guard teams. (We also made a few for the State Department security folks as they also liked the accuracy of our 1/9 barrels better, but mostly they were buying our Uzi barrels at the time.)

And of course there are many more heavy bullets available today than back then, and there were no nitrided barrels or Wylde chambers at the time either. 1/12, 1/9, and 1/7 were the only available options in chrome lined barrels back then, and the M4 was still in the process of being tested. The green tip SS109 was the only military ammo at that point, and it's accuracy sucked. (Still does from what I understand.) So while this barrel twist information is probably dated now I've never seen anything as definitive published since that would make me disbelieve those results myself.

But my experience is mine, and other folks have other experience. I'm just putting mine out there for folks to consider since it comes from a manufacturer, YMMV and all that.

 

[brunop]

When we were doing accuracy testing in the mid 90's at Bushmaster we spun up multiple barrels on 1/9 and 1/7 chrome lined blanks in the same profiles from 11.5 inches up to 20 inches, as we were pursuing a government contract at the time. In our testing which involved eliminating as many variables as possible and testing twist rates only head to head, we found in our testing that using the same ammo in the same barrel length, a 1/9 twist barrel will outshoot a 1/7 twist barrel regardless of the barrel length being tested. This testing was the primary reason Bushmaster stayed with the 1/9 rifling twist for so long.

Got it - thanks for the clarification.

Also, I'm wishing I'd just bought 1/9 twist barrels for the 55 gr. stuff. I almost never shoot 75s or 77s because I don't want to spend the money and I don't think the juice is worth the squeeze.

Good info - thanks again.

 

[NFADLR]

How about a 20" 1/8 whats the proper projectile weight ?

Correct with green tip, 62 grain ?

 

[Firemedic8998]

A 20" Wylde chambered 1/8 barrel will shoot pretty much anything you can buy over the counter, but reloladers might want an even faster twist if they plan on using very long, very heavy VLD bullets for extreme long ranges. (I prefer a 55 grain boattailed projectile in a 20" 1/12 barrel myself, but I'm pretty old and cranky and feel like Stoner and Sullivan kind of got it right the first time so I don't mess around much with this newfangled stuff in my own guns.) A 1/8 twist should prefer heavier bullets of around 75 grains and should stabilize a 77 gr OTM just fine from a full length barrel.

Stability in flight depends more on the bullet length than the bullet weight, and the velocity has to be high enough for the bullet to reach a certain rotational speed, which again varies by projectile. This is a separate number from the ballistic coefficient, which mostly measures atmospheric drag. External ballistics is an extensive field and you can go as deep into it as you want, there's always more to learn. There are a ton of folks out there that know way more than I do about that, but I have been part of some testing along those lines.

In the past Green Mountain Rifle Barrel has made experimental 5.56/.223 barrel blanks with twists as fast as 1/5, and they currently are offering a 1/6 for folks that really want to have some rapid rotation in their projectiles. I'm not sure what other barrel makers like Krieger or Bartlein are doing for their twist rates. There are makers that manufacture 90+ grain .223 bullets these days, and those really stretch the envelope for the cartridge both for range and for physical size, as at least some of those loads are too long to fit in a standard magazine. Those might need a very fast twist to stabilize, although I wonder how far those heavy projectiles can really go before dropping back through the sound barrier and losing some accuracy in the process.

I have read that the various Blackout cartridges all can use a very heavy bullet and a very rapid twist for their subsonic specialty loads but I don't have any firsthand knowledge of those. I have to wonder about the projectiles though since early in the 1/7 days there were issues with some of the thinner jacketed varmint bullets actually disintegrating in flight due to the rotational speed exceeding the material strength of the projectile. Modern varmint bullets are now made with thicker jackets to withstand the strain.

Sorry, it's late and I'm wandering. Again, a 1/8 twist should prefer heavier bullets of around 75 grains and should stabilize a 77 gr OTM just fine from a full length barrel. Hope this helps.

 

[raubvogel]

Funny you mentioned 1/12 out of a 20" barrel. This is what I got. As soon as I get my upper back -- M1A1 upper and front sight -- I would like to try it out for distance.

 

[hueyville]

I have two 12.5" AR 15 builds that shoot sub 1 MOA and with my test scope they shoot 5/8" to 3/4" five shot groups from the magazine though one wears a aluminum chassis 2 MOA dot size C More at present and the other wears a Leupold 2-7x illuminated reticle in PEPR mount with Burris Fastfire II on top for CQB work. I believe (actually 95% sure) have two more of the same barrels in locker at work. From one of my box of factory blems, test barrels and over runs from WOA.

Back when buying barrels almost daily during late Obama/early Trump Administrations when we were living in the best times for builders ever seen or to be seen again. Called WOA and asked Jan if she had me anything? She said she had a couple of test barrels each with 50 rounds down bore along with pair of 26" 5.56 barrels the engraving department put wrong twist rate on tube (I care not as that's hidden under handguards but actually scrubbed the twist, Cerakoted then built both. She also had four 12.5" 1:8 twist Bartlein single point cut rifled air gauged tubes from a special order for an alphabet agency that wanted shortest barrel that could still make precision shots.

I built both on SIG upper receivers I hand selected for suggest possible fit to barrel extensions. Squared the uppers then used my ultra secret bedding compound and torque method John had told me about him using when wanted best precision from an upper assembly. One got a 3.5" KAK flash can (very similar to Noveske Flaming Pig) and with an extra thick washer it made 16.15" from bolt face to very end of device using my "no lie" AR barrel length gauge that goes down bore and had my machinist make a scale with small tick marks every tenth of an inch and larger mark with number stamped at every inch. Used a Colt M16 full auto carrier with a carrier weight to increase mass even more. Used a JP high pressure bolt.

Used a machined billet lower with Tubbs flatwire buffer spring, Hiperfire Hipertouch 24E trigger with their 2.0 pound spring kit and my digital trigger gauge always shows those Hiperfire Hipertouch springs to give exact pull advertised from 2.0 to 4.5 pound in 0.5 pound increments. Installed test scope (Horus 8-24x with H25 reticle) and went to range using Tubbs 69 grain DTAC ammo. (Use the Tubbs DTAC as my test ammo for most 5.56 builds) This group of barrels are fairly fat for stiffness as contract was for accuracy in a short barrel and they were never sold as a company "product" to my knowledge. They always make a few extra on such deals, test one or two then hold a couple extra in case customer complains about one they don't have to retool for a single barrel. I buy all the over run/blem/test barrels at a flat rate but have to take every barrel in the pile.

Went through a break in cleaning after each round for 1st five shots then every three round for five cycles then pushed a wet then dry patch down bore every ten rounds for thirty more rounds to make sure was not seeing any copper fouling indicating a rough spot in throat or bore. As I did break in I swapped in a buffer one weight heavier, then two weights heavier watching where brass landed so rifle was tuned at end of break in.

After the break in got serious and began running five round groups and all were 1 MOA or less except shots I knew I had made a mistake as the operator, not the rifle. It was easy to shoot 1 MOA and when I accidentally didn't mess up a string it was shooting 5/8" at least one of three groups, 3/4" one in three and one in three groups I threw a shot, actually pushed them using too little finger on the trigger which is my nemesis of trying to hard to be easy and don't get enough pad on a light trigger where I can hook a 4 pound or heavier and just let fly.

After ran 100 rounds had at least a half dozen 5/8" groups and same number holding 3/4". Before left range pulled trigger and put a 3.5 pound spring kit in it, pulled test scope and installed my C More 1x red dot. Was able to shoot 1" with red dot a couple times but was just blind luck as 2 MOA dot at 100 yards center of target is obscured as are any bullet holes unless way off point of aim. Built a second of these barrels when my Form 1 came back for an SBR and terminated barrel with a quick change suppressor adapter. With test scope, 2.0 pound trigger and no suppressor it shot basically same as the first once broken in. With can snapped on best groups (not best group but best aggregate of smallest groups) went to 7/8" with 1 1/8" being next node of group sizes and 1.25" being about worst unless I called a shot bad second rifle barked.

When finished break in, tuning and testing of the second I put a Vortex Viper PST 1-6x on it then a 3.0 pound spring kit in the trigger and it shot 1.5 MOA off the bench like a machine. I seldom go under 3.25 pounds on short barrel rifle triggers so eventually swapped the springs from 3.0 to 3.5 pounds like it's brother. Was not liking the 1-6x as at 1x the eye box was too small and when added a half pound of trigger pull was harder to work longer shots so put Leupold 2-7x in PEPR mount with Burris Fastfire II 1x red dot on top and if do my job it shoots 1".

They were able to get two of these barrels out of each Bartlein 1:8 blank so they sold me the 12.5" tubes a bit cheaper than my normal price and plan to build the other pair when I can afford to SBR them and top them with a nice 1-10x LPVO or maybe a compact 3-12x or 3-15x with a red dot on top. If you can find the right 12.5" barrel you can most definitely get sub MOA accuracy.

 

[hemcon9]

I had several Bushmaster barrels back in the day, early 90’s.
I bought several select fire bushmaster carbines with 14.5” length and 1/9 twist.

Also had a couple 20” govt profile barrels.
Bushmaster was often mocked as their quality was hit and Miss but the barrels I had performed very, very well.

I still have a 14.5 barrel that I replaced after about 10,000 rounds, mostly full auto fire. I sectioned the chamber on the mill so I could examine the chamber and throat.

The throat, lead and beginning of the bore look like the back of an old alligator but that barrel was still shooting quite well when I pulled it.

Say what you want about Bushmaster’s hit/miss quality and crappy fit/finish. The only issues I had with their select fire guns was their crappy bushmaster branded magazines and their extractor springs.

The extractor springs would heat up after a few full auto mag dumps and go soft, putting the gun out of commission.
Replaced them all with Wolffe extra power springs and never had an issue after that.

 

[hueyville]

Funny you mentioned 1/12 out of a 20" barrel. This is what I got. As soon as I get my upper back -- M1A1 upper and front sight -- I would like to try it out for distance.

Twist rate of barrel is not as important as the quality of the men who meticulously make them. Then if compare apples to apples on quality then longer is better to reach out and touch things.

1:12 twist you say? I have two of these Krieger 26" 1:12 twist 11° target crown rifle +2" gas single point cut rifled air gauged...... barrels built and have two more put back. They will stabilize 77s just fine but currently both are sighted for 52 grain SMKs and can get on an active prairie dog field where start heating up bore of one and swap to the other then back always keeping a warm rifle but not throat burning rifle to kill the little buugers wholesale. With any good quality 52, 55, 62 or 69 grain bullet both will shoot five rounds into basically a single hole at 100 yards.

Honestly unless hunting varmints neither are even fun to shoot paper at 100 yards because they are so stinking accurate, a group big as 3/8" just shows I am having a bad day or it's windy and not reading wind speed at target well enough to know when to break each shot. These shoot at 250 yards like some of my factory 20" HBARs shoot at 100. It's why I have so many 24", 26" and 30" straight taper barrel single point cut rifled AR 15s and AR 10s with +2", +3" and even +4" gas systems. Take a super well made bore, precision cut chamber in a fat stiff long barrel, as near perfect cut crown machines can cut (sometimes threads for flash hiders or suppressor adapters take away that last bit of good) with lazy gas system to ensure longest possible lockup time and it's possible to cobble together gas guns that run like custom bolt guns.

Most of these barrels were never part of some vendors normal inventory bot the extra units from some special order or a barrel someone made their 50% deposit and never paid the rest after it was finished. I like mine FAT!!!



Six plus pounds of AR 15 barrel and have some AR 10s that go heavy as eight.

 

[raubvogel]

@hueyville you do have a point. And some nice barrels. I have always been told the two most important parts of any rifle are the barrel and the bolt (and how these two lock against each other); the rest is there to support them. I too prefer longer heavier barrels, and rifle (did not know you could get them longer) length gas systems, if I can get away with. Case in point is the first barrel I bumped into for my M16 parts kit: it sure looked amusing in the picture but I quickly realized it would not work out because I did not want to modify the original bits.

Honestly, I have no idea what who made it or what it was supposed to be for as its barrel dwarves the poor gas block. But, it looked mostly unused (the threads look clean but as the second picture shows, it looks a bit shiny in a spot) . And it has the straight profile for most of its length you mentioned. With that said, I ended up getting the thinner (hopefully right profile for the kit) 20" barrel you have met. Which did not have the sight pinned, but that is another story.

I think my AR in 308 barrel is also 26" long and thick (.936 gas block; would like to find an adjustable one but it seems they stop at .750?), and it shoots better than me (not that hard); no clue of who made the barrel though. But, I would not want to be running with it on my shoulder...

Impressive collection of barrels you have!

With that said, I remember you said that properly installing the barrel in an AR does make a difference if you are going for accuracy. In addition to having a well-done barrel, that is.

 

[STG_58_guy]

If you are shooting from a bench, a 20” rifle length gas system with a heavy profile with an A3 upper and quality glass is the cat’s ass man. Smooth, compliant, and at peak ballistic efficiency for the cartridge. As you go shorter, the compromises gain amplitude. You know there is no free lunch.

You contradict yourself, so it’s hard to read what you are really asking. You say you don’t need a 20” but you only shoot from bench, then you say short ARs feel wobbly but you have a 12.5” in your title. Seems your wants & practicalities aren’t on the same plane. Accurate ARs come in all configurations, just depends on your application, skills, & ultimate objectives.

Not at all. I have awhole bunch of 21 inch rifles and three in the 26 heavy barrel category. I like short rifles too. I haven't quite mastered them off the bench yet. They are a lot easier to bang steel with at 50 - 100 yards. I can't hardly hold a full size rifle still shooting offhand.

 

[STG_58_guy]

"1/9" twist will outshoot any 1/7 twist with bullets under 70 gr. across the board". "I very much expect that this is not true across all bullets and all loads, so your fave ammo purchase or 'recipe' is going to figure into this question."

I should have made this more clear. When we were doing accuracy testing in the mid 90's at Bushmaster we spun up multiple barrels on 1/9 and 1/7 chrome lined blanks in the same profiles from 11.5 inches up to 20 inches, as we were pursuing a government contract at the time. In our testing which involved eliminating as many variables as possible and testing twist rates only head to head, we found in our testing that using the same ammo in the same barrel length, a 1/9 twist barrel will outshoot a 1/7 twist barrel regardless of the barrel length being tested. This testing was the primary reason Bushmaster stayed with the 1/9 rifling twist for so long.

Obviously the 77 OTM grain ammo was not available back then and the heaviest projectile we tested with was a 69gr Berger IIRC, as we knew the 1/9 would not stabilize anything heavier in a short carbine barrel. We ended up winning the Department of Energy contract with our chrome lined 1/9 twist M16A2 barrels as they were not going to be using tracers, and our submitted 1/9 barrels won the accuracy competition portion of the testing by a substantial margin over the 1/7 barrels being fielded by the other competing manufacturers. So there's that factual information and it can be researched and verified if anyone's interested. I don't recall the GSE contract number but it was one of the few U.S. government contracts that Bushmaster ever actually won, and it was for the DOE nuclear material guard teams. (We also made a few for the State Department security folks as they also liked the accuracy of our 1/9 barrels better, but mostly they were buying our Uzi barrels at the time.)

And of course there are many more heavy bullets available today than back then, and there were no nitrided barrels or Wylde chambers at the time either. 1/12, 1/9, and 1/7 were the only available options in chrome lined barrels back then, and the M4 was still in the process of being tested. The green tip SS109 was the only military ammo at that point, and it's accuracy sucked. (Still does from what I understand.) So while this barrel twist information is probably dated now I've never seen anything as definitive published since that would make me disbelieve those results myself.

But my experience is mine, and other folks have other experience. I'm just putting mine out there for folks to consider since it comes from a manufacturer, YMMV and all that.

I appreciate first hand data. Thank you. Is it possible your tools were efd up for making the 7 twist barrels? Probably not.

 

[Firemedic8998]

Not within the limits of our air gages and optical comparator equipment, no. Those bores and chambers were all as good as they get with button rifling and CNC lathes. Don't know if Wylde chambering would have made any difference or not, it hadn't been invented at the time.

Tangentially, it seems there aren't too many match rifles being made in 1/7 from what I read. 1/8 seems to be much more popular rifling for the heavy match bullets. I suspect it's related to our findings.

 

[hueyville]

Earlier in thread I posted about getting 5/8" five shot groups out of one of my 12.5" Bartlein's and 3/4" from the other at 100 yards. In testing they were still shooting well at 250 yards but velocity drop was becoming an issue to point I would not expect bullets to properly expand or do whatever are designed to do by 400 yards. Comparing velocity of a 12.5" barrel (length OP was specifically speaking of) to that of a 20" may not effect accuracy on a very good barrel horrendously but it is going to affect velocity to point bullet may not be terminal at distance. Using chart rather than actual measured velocity of single load in single barrel since all barrels are different and all loads are different I would say a 300 fps velocity loss at muzzle between the two at muzzle. That loss at muzzle is going to translate to even larger losses at extended ranges as its not linear, a slower bullet at muzzle usually loses velocity at a more pronounced rate than a faster projectile.

I have found significant like nearly 100 fps velocity difference in same length barrel with 5.56 shorties if compare a match wylde chamber and air gauged single point hand lapped barrel or 3R compared to some slightly oversize chamber through a rough button rifled barrel with a rough surface. Then add lock time into equation and someone has done their build with not only a rough/generous size chamber tube but has a super light carrier/bolt that unlocks way sooner than say a full auto carrier possibly with carrier weights added and maybe even a "rate reduction" buffer to really slo0w down the cyclic rate and bolt in the over sizce hamber/rough bore is unlocking about as fast as bullet reaches muzzle while the better barrel has a bolt that is locked up tight till bullet is cooking own range and then you can have two 12.5", two 16" or two 20" shooting the same bullet at significantly different muzzle velocities.

Think about that bullet going down a six or seven groove bore that's rough as sandpaper (bit of exaggeration) and chamber not sealing as quickly or completely compared to a tube case chamber seals in chamber about the instant primer lights and bullet runs down a precision single point or 3R bore that's smooth as glass. Add in the better fit chamber/smoother bore without any constriction points and there are a ton of variables that come into play. The only lightweight carriers I own are in the parts lockers and more likley to add weights or heavy buffer to slow my bolt unlocking than one of those lighter carriers. I will through an MGI Rate Reduction Buffer in without hesitation to slow rifles 50 to 150 rounds per minute. Unless its a quality barrel made for military fighting rifles I put match grade barrels in most lengths,

I do like FN CHF melonite barrels for fighting carbines but if can score a Lothar-Walther 5R with their version of melonite I will and its noticeably faster velocity and more accurate than the FN made for military service. Have worked with barrels others provided and thinking of one particular heavy taper 20" HBAR that I knew was going to have issues when did my bore scope inspection out of the box. I built his upper, took it to range with barrel as shipped to range and every round could see it copper fouled from throat to muzzle and after twenty rounds cleaning after each round it was not getting better on fouling and could tell it was not getting good accuracy. I took it back to shop, hit it with a throating reamer which proved my suspicion the neck was slightly out of square, hand lapped it and touched up the crown. Took it back to range and it was definitely fouling less and shooting faster (was using a chronograph from shot one in break-in process) but I decided to use a few (not the complete kit) Tubbs "fire lapping rounds" and then finally saw the copper fouling issue really improve along with the pores in steel in that first half inch or so of rifling smooth up enough bore was not pulling jacket of the bullet from the instant it made the leap across the free bore to rifling.

Just like triggers I have found some barrels can be helped greatly with hand lapping and some touch-up work from the get go. Having some finish reamers, throating reamers, know how to hand lap or fire lap and touch up crowns if a good inspection with your bore scope shows evidence of issues you can take some lower to mid quality barrels and help them immensely. Its like going to the effort of squaring the upper receiver which is huge on some uppers, bed the barrel into the reciever properly, use correct torque on barrel nut and sometimes change torque value on muzzle device or swap to a totally different muzzle device that calms your barrels harmonics down a person can take mid grade parts and build pretty nice rifles. I have broken in OEM mid line to upper line rifles then tore them down and spent a couple days hand fitting parts from trigger to upper and barrel then with nothing more than possibly a spring kit and buffer swap increase its accuracy 1/2 MOA or more.

While you can get accurate short barrels you can't recover all the velocity los between a 12.5" and 20" tube. I have more 14.5"/14.7" and 18" AR 15 barrels than all other lengths. I am not a fan of 16" and only buy them when they are super deals. @0" heavy taper barrels are just enough forward heavy they give me some issues shooting off hand for long now and found that a good 18" barrel balances much better for me and shoots to withing 95% or more of what a 20" shoots except for big long fatties plan to shoot off a rest of some sort 18" is my barel of choice for distance work with my 6.8, 5.56 and 22 Nosler ARs. I have a few medium weight 20' builds I still carry as general purpose, especially one medium taper 20" 3R 22 Nosler and one of my medium taper 20" 5.56s but if have the choice I grab 18" tubes now if plan to hump it around and shoot it off hand on occasion. But overall accuracy is most affected by using a good barrel then eliminating every bit of tolerance stack possible.

Anyone building ARs or has built more than a handful and not squared their uppers then bedded extension into upper and used a torque wrench when snugged the barrel nut needs to buy a Wheeler tool to square uppers, some beding compound and torque wrench. then one at a time test accuracy of your builds as they sit now then again after they go through the process of pulling off the front end and going through these three steps. Bet after you do this to your first unit and test it will be in a hurry to do the same to your others. Because of collector value my old Colts are only rifles that don't get this done.

 

[STG_58_guy]

@hueyville 12.5 because my modeling software says 5.56 with 55 gr - 62 gr pills burns up 100% of the powder well before 12.5 inches, which I can hardly believe. According to models, 12.5 should be very efficient. 2400 fps out to 100 yards is 'splody for most V-Max type bullets. Nosler BTs. Anything from Barnes. Tipped SMKs. Pooof. These will change a fellow's mind... into pink mist.