Optimum barrel length for SBR

[Calico Jack]

What's the optimum barrel length for a 5.56 SBR? I was considering a 12.5" but finding 11" or even 10" free float hand guards has been difficult. I would rather not use a blast forwarding device. Can I run a 12.5" barrel on a 12" rail with a vg6 gamma ex? Or am I better served going with a 11.5" barrel and 9" rail.

[alamo5000]

Optimal barrel length is going to depend on what you want to do and at what ranges you are looking at doing them.

We have had this question come up several times in the past so here are a few notes:

Ammo: Either shoot 77grain or 75 grain ammo for the best reliable performance. Out of a 10.5" 5.56 SBR that gives you a reliable range of around 50 yards for bullet performance on barriers and soft explody smooshy things. Beyond that it's still not going to feel good but per previous data and research by Molon 50 yards is a good effective range for that barrel length. Do not count on 55 grain ammo for anything but plinking. The heavier the better. Like I said 75 or 77 are fine.

A longer barrel even 1" longer provides some more velocity and helps with this and also increases dwell time, which is the time the bullet has between passing the gas port to exiting the barrel. Some people have reported that 10.5 rifles can be finicky but mine runs like a champ. Word on the street is an 11.5 is a very good medium.

Other people swear by it, even the late great John Noveske thought 12.5" was the optimal length for a variety of reasons.

On the rail system it's going to depend on a number of factors. For the most part if you take your barrel length and subtract .7 or .8 inches you would have a tight fitting suppressor with clearance so adjust accordingly.

Some manufacturers are either long or short on their actual numbers, some by design. Say for example one barrel maker that produces 12.5" barrels actually makes them 12.7" or something like that so there is good fitment with handguards and suppressors.

Just because it says 11" on the rail in a lot of cases it might be 10.9 or 11.1 or whatever.

Also note that the trend for ultra slim handguards with a tight inner diameter might dictate what brand of gas block you use, depending on a variety of factors.

The only company that I personally know of (but then again I am not as knowledgeable about products as the other guys here) that makes odd lengths designed for fitment is SLR. They make handguards that are say 10.7" or 9.7" or whatever.

There is no one answer to what is the optimal length of barrel. The quality of barrel and porting will determine a lot more than the length. Most people though have reported from 11.5 and up they have had no issues. I have had zero issues with my 10.5 once I got it all honed in with the right buffer weights and whatnot.

[fledge]

Yes, you can run a 12” rail with a 12.5 barrel. The handguard May cover some threads but the muzzle will be clear.

I run a 12” noveske and SMOS handguard over 12.5 barrels. With a dead air mount, I’m still able to attach a suppressor with almost no gap.

Some measure their hand guards and barrel lengths differently. So be aware of that.

[DISCOM]

You should look at SLR Rifle works. When I built my 12.5 they were the only company that I found that made a 11.7 and, the measurements that they give are true top rail length.

Great guys and LEO/MIL friendly.

https://slrrifleworks.com/index.php?route=product/category&path=135

[Uffdaphil]

11.5 was my fave w/o a can and 10.5 with. But then I built a 12.5 and it is my go-to now in either configuration - great balance and softer recoil. But a lot depends on which components. The 10.5 is kinda chunky with a quad rail while the 12.5 has a light SLR mlok. With others nearby I never shoot an SBR with a brake sans can unless my taper mount blast shield (Recce5/7) is covering it. And even with a flaming pig the 7.5 is an obnoxious critter, but fun.

[alamo5000]

- great balance and softer recoil. But a lot depends on which components. The 10.5 is kinda chunky with a quad rail while the 12.5 has a light SLR mlok.

Good point. If you are shooting with a can (or without) the balance will matter. I've picked up some other supressed SBRs and geez, they were to a point of being uncomfortable because of balance mismatch. I am used to my gun and with or without the can it's 'nimble' and balanced. Those others with those rails and those specific suppressors etc the guns were extremely nose heavy. That would get extremely irritating to me over a long time.

In other words I am glad I went with quality parts and took the time to think through what I wanted.

Even if you go to a really good gun store just eyeball and finger bang some of their various setups and it should give a good idea about what the feel would be. In my opinion an overall slightly heavier gun with better balance is better than a lighter gun with a bad balance.

[BoilerUp]

I like Garand Thumb's video on the topic. Spoiler alert: 11.5" suppressed, 12.5" unsuppressed


https://youtu.be/Mxwi9fAe4s8

[alamo5000]

I like Garand Thumb's video on the topic. Spoiler alert: 11.5" suppressed, 12.5" unsuppressed


https://youtu.be/Mxwi9fAe4s8

I like that video. Very good info.

[Joelski]

You can get sucked into the reasoning that you see better velocity from longer barrels, which is true, however that defeats the point of an SBR. Too short of a barrel and the weapon becomes un-manageable with a suppressor, with burning gases outrunning the can.

The best balance of length and noise/signal control (with a non-k silencer) have been well-established and continues to be 10"-11"" for 5.56, and 8.5"-9" for .300 BLK.

[BoilerUp]

What's the optimum barrel length for a 5.56 SBR? I was considering a 12.5" but finding 11" or even 10" free float hand guards has been difficult. I would rather not use a blast forwarding device. Can I run a 12.5" barrel on a 12" rail with a vg6 gamma ex? Or am I better served going with a 11.5" barrel and 9" rail.

I've got an 11.5" barrel under a 10" BCM KMR-A and there isn't too much room to spare. I love the BCM handguards, btw.

https://photos.smugmug.com/photos/i-CDKXXKv/0/ee66a556/X2/i-CDKXXKv-X2.jpg
https://photos.smugmug.com/photos/i-rhVtt5v/0/d5f32170/X2/i-rhVtt5v-X2.jpg

My 6.8 SPC is a 12.5" barrel under an SLR handguard. I think it's an 11" handguard, but I need to go look:
https://photos.smugmug.com/photos/i-Gc5zqkN/0/2c68ea62/XL/i-Gc5zqkN-XL.jpg

[cjd3]

I’ve had the same question for my current build, thanks for asking, and thanks for all the answers.

[voodoo_man]

LOL @ that video.

MK18 upper is basically the best in the business, both canned and non, as far as price goes.

If you wanna get fancy get a KAC SBR upper 11.5", again both canned and non, best of everything and you pay for it - https://www.knightarmco.com/12012/shop/commercial-firearms/sr-15-e3-cqb-mod-2-m-lok

Everything else is meh and/or niche specific.

Whatever you choose you need to be able to use 77gr OTM to do sub MOA groups at 100y. If it cannot do that get something else.