11.5" vs 12.5" 5.56mm

[Lance Henze]

What is everyone's opinion on 11.5" vs 12.5" when it comes to a 5.56mm duty rifle?

If you'd like, feel free to throw in 10.3"/10.5"/MK18, but I feel the general consensus is 11.5" > 10.5" functionally speaking. Is there any good reason to take a 12.5 over an 11.5?

 

[Matt Landfair]

Thanks @Lance Henze

 

[Lance Henze]

Side note: BCM doesn't appear to offer any BFH barrels in their 12.5" upper line. Not sure why this is. 11.5" seems their go-to.

Not to derail the topic, but for documentation purposes if the 10.5 vs 11.5 debate does come up. Here's the ol' staple response from BCM back in 2009.
http://www.ar15.com/forums/t_2_138/174764__Q__Why_BCM_chose_the_11_5_SBR_over_the_10_5_.html

Back to 11.5 vs 12.5...

 

[Dr. No]

I run 12.5" noveske barrels and I love them. Great accuracy and increased velocity. With a can it's about a 16" gun. I wanted the best terminal performance I could get out of a small package.

 

[Lance Henze]

Velocity Differences:
Obviously there are a variety of factors here, the main one being ammo selection to include powder type, volume, etc. Velocities will vary, but generally speaking my findings with 11.5 vs 12.5 are ranging between 25fps and 90fps. 25 being pretty darn negligible in my opinion, but 90fps (and anything above that) is getting up there. Can anyone confirm with any chrono results and ammo type?

Some other things that would be nice to hear from someone with first hand experience include:
Dwell Time
Chamber Pressures
General Reliability
Suppressed Performance
General Experience

 

[Dr. No]

I saw about 125fps difference between my 12.5 & our 11.5" commandos. Those are older so they may be a little shot out too.

The gun cycles very smoothly - ejection is very consistent at 3 o'clock.

I literally have had 0 issues with my Noveske 12.5 until I put the can on. Before that I could get 1000 rounds through with just adding lube. Once being run suppressed, it went down to about 180-210 rounds before I started to have failures to feed. I put an adjustable gas block on (micro MOA) and I have not had a chance to shoot it to failure yet, but I have gotten through around 400 rounds without a failure suppressed. Ejection is back to being very consistent at 3.

I'm not an engineer, but I would imagine the more dwell time you have, the lower pressures the gun generally has to contend with.

 

[adam_s]

This may be a variable too far, but along similar lines-I've started seeing 12.5" barrels coming out with midlength gas systems, as opposed to the standard carbine seen with a 12.5" barrel. Any input on that course of action?

 

[Dr. No]

More dwell time is good for reducing pressure and cyclic rate. So long as the gas port is the right size it should be great.

 

[Lance Henze]

I hear enough bad things about 13.7s with mid-length gas systems and the occasional 14.5 middy problems too. I'm not sure I'd go for a 12.5 in a mid-length. That is going to make dwell time even shorter - not longer. For the purpose of this discussion it might be best to stick with carbine vs carbine as I'm sure any 12.5" middys are few and far between.

Pulling down the responses on the FB post too. See below:

• 
• John SalingI have several 11.5” (bcm x2 & dd chf) and 12.5” (noveske regular and chf & bcm ss410) and I have used everything from 55g Russian shit to mk262 with boring regularity. I’m no champion marksman but I shoot allot and have seen no appreciable difference...See More
  April 10 at 12:49pm · Unlike · 1
• 
• Matt HelmJohn Noveske said that 12.5 was his idea of the perfect 5.56 barrel length, back when I ordered my first Noveske. Mine ran great with and without a can. Very little it can't do.
  April 10 at 1:32pm · Unlike · 2
• 
• Matt LandfairLance - since this topic has come up multiple times, I task you with posting your exact same question on the forum so we can provide that link to future similar questions.
  April 10 at 1:55pm · Unlike · 1
• 
• Pat DeSarnoI have 2 10.5 inch, Noveske barreled Colt's. I have done several classes with them and have never had a reliability issue with either one suppressed or otherwise. The gas port size Noveske uses with their chrome lined , 10.5 is .071. The original Colt ...See More
  April 10 at 4:24pm · Edited · Unlike · 1
• 
• Pat DeSarno
  
  April 10 at 2:54pm · Unlike · 1
• 
• Corey SherwinPat DeSarno, what is the gas port size?
  April 10 at 3:50pm · Like
• 
  Pat DeSarnoWell, I must be getting old because after consulting with Robb just now he assures me the 2 port sizes were indeed different. Forgive me boys it's been a few years. The Colt Mk18 barrel gas port measured .093 and apparently the Noveske measured .071. I will edit my above post to reflect this.
  April 10 at 4:16pm · Edited · Unlike · 1

 

[rob_s]

Mid-length gas on a 12.5" would be equivalent to rifle-length gas on a 16" gun. Could it be made to run? Sure. Would it take some work? Probably. Is there any benefit? Probably not. Would it be worth the trouble? No, not to me it wouldn't.

To the original question, were I going to own just one AR, and was willing to deal with NFA for that one AR, and was willing to accept the concessions from doing all of that, I'd have a 12.5" Noveske stainless with Switchblock. It wouldn't do any one thing perfectly, but it would do a lot of things well enough. I'd put a 1-6x optic on it and call it good.

To that end, for a "patrol rifle", that might be a good option as well. If a can just isn't in the cards for a patrol rifle, skip the Switchblock. If you're not going to put a magnified optic on it, skip the stainless and get the N4 profile hammer-forged barrel. If you're only going to run it suppressed, get the 10.5" barrel, no Switchblock.

Expanding the scope a bit, for folks that have a 16" gun already, I think the 11.5" barrel is the best compromise when running without a can. Short enough that you get some benefit in the weight/length department that you can actually appreciate, and long enough to that you're more likely to get better reliability. The 12.5" is too close to 16" for my tastes, and the 10.x is still (even in 2015 when we can make 10.x guns run really well) a bit of a ragged-edge gun. 10.x,mhow ever, starts to make sense if you're doing a dedicated suppressed gun, and I'd do an adjustable gas block to get it tuned initially and then "set it and forget it".

 

[rob_s]

Well, color me surprised, Noveske no longer sells a complete upper or carbine with the 12.5" Switchblock barrel, in N4 or stainless flavors.

What they used to have, that I'd go to if I was doing only one gun, was this gun but with a 12.5" barrel with a correspondingly longer handguard with Switchblock cutout.

 

[adam_s]

Coming back to the 12.5" middy gun, I had a chance to run my Triarc TRACK 12.5" fluted middy with my SilencerCo Saker762 over the weekend. Only limited shooting (90rnds all Federal XM193), but no issues at all to report. Using a Geiselle gas block, Triarc NiB BCG, and VLTOR A5 system with the "standard" A5 buffer (5.3oz, so an H3 buffer essentially). Bolt locked back fine, ejection was steady, and no apparent case damage. Recoil was a bit snappy, so it could have been a touch overgassed, but better a touch too much gas as opposed to too little.

I've got a Centurion Arms 11.5" carbine upper as well. I need to fire both uppers (12.5" middy and 11.5" carbine) back to back with the same lower and my suppressor to offer a better comparison between the two.

 

[WDPD8207]

Tagged for interest

 

[CrazyDoc]

I have a BCM 11.5 that I run with or without a can (SPECWAR 556) that runs like a champ. Dirty as all hell but it runs great.


Toole

 

[Dodge37]

Does anybody have times with data comparing both. Like I have short a -2 modified Navy qual with 14.7 Midlength light weight SOOGW w/ A5H2muzzle device Surefire war comp (got lucky). Try the same thing with the 11.5 reduced gas port sionics pistol with A5h2 and SOLGW NOX that I scored a 19 on.

Have no time on 12.5 to give any data on.

 

[Dodge37]

After testing yesterday the 11.5 pistol can run on A5H3 doing the mike pannone reliability test.

 

[shoobe01]

Do not have both so just one point, but I have a BCM 12.5 upper I run both suppressed and not, love everything about it. Works flawlessly, accurate as all get out. How do I tell which type of barrel it is?

I have chrono numbers suppressed (cannot get the magnetospeed on the bare barrel) on a bit of paper... at home.

 

[henschman]

After testing yesterday the 11.5 pistol can run on A5H3 doing the mike pannone reliability test.

What's the Mike Pannone reliability test?

 

[Dodge37]

My understanding of it from an article I can’t find anymore, and read it years ago. How I did it was to have a the chamber loaded as well as a fully loaded mag inserted on first shot and empty mag on second shot to make sure gun locks back on empty. Handguard rest on the open palm of your left hand, and the right hand loosely holding the back end of the gun. (Pulled trigger with thumb) You are standing on the opposite side of the ejection port. Not having the gun in your shoulder makes sure the system can run on its own and should gain reliability once in your shoulder. On one of the modcast Chad (borebrush) talked about doing the man test which is his version of the same thing where you shoot it at full extension and both hands on the pistol grip. Stock not on shoulder.