Preferred 5.56 SBR length

[OJ didnt do it]

I’m looking to build a MK18 style SBR and I don’t care about staying true to the original specs I just like the general setup.

I’m wondering what you folks prefer in terms of length for 5.56 SBR; 10.5, 11.5, or 12.5?

I’m not a fan of .300BLK although Im not closed off to it. I will probably get one at least 10.5” or shorter in the distant future so for this purpose I’m looking at strictly a 5.56

I would be putting some type of break or flash hider, undecided, and a Surefire warden on it first. Later on I’m hopefully putting a can on it but that is less certain so I would like something that’s nice to shoot in the meanwhile.

Everything I read seems to say the 11.5/12.5 does everything a 10.5 can but better. I’m sure it does but there’s a big group of people that say 10.5 is the preferred setup.

Anybody have something like this that I could shoot and try out before I invest? I’ve never shot shorter than 14.5 so I don’t know what to expect really besides what I’ve researched. Willing to provide ammo or pay of course if my ammo isn’t the correct type. I’m in Mass.

 

[LakeTrout]

If those three were my only choice, I'd go with the 12.5". The shorter you get with a 5.56, the more unpleasant it is to shoot. Bigger flash, louder noise, etc., and you really begin losing critical velocity that this round needs to perform. Maybe its a range toy or a gun you are keeping incase you get in a fight in a bathroom and you're not worried about the loss in velocity affecting range. Actually, that brings up the question that should probably be asked first. What is your intention for this setup? Its intended use really is going to determine what barrel length is ideal.

One thing that always gets me is guys that go ultra short on these setups and need to put a can on it just to make it somewhat enjoyable to shoot. Some people don't mind all that blast, and thats fine. I think the majority of us probably want it tamed a bit. But 5.56 in a short barrel isn't going to supress all that well. And you end up introducing a whole set of other issues/variables with your setup by sending that much extra gas back at your face. So its funny because you end up seeing a lot of folks with 5.56 SBRs and a can which gets them somewhere around that 16-18" length that they would have started at, a lot more weight, and not really too much quieter than if they had gone with a 16-18" barrel.

Some of this is an exaggeration, but I hope you can see the point. You can start chasing things around like shorter length barrels to make it set up for what you want in your mind, but you end up chasing all of the issues you created until you are back where you started in terms of length, only with a smaller bank account and less velocity.

This doesn't mean SBRs in 5.56 don't have their uses or aren't fun range toys. Just food for thought and a suggestion to think all of these things through and build deliberately to a speciffic purpose.

 

[Da_lucche]

I’m looking to build a MK18 style SBR and I don’t care about staying true to the original specs I just like the general setup.

I’m wondering what you folks prefer in terms of length for 5.56 SBR; 10.5, 11.5, or 12.5?

I’m not a fan of .300BLK although Im not closed off to it. I will probably get one at least 10.5” or shorter in the distant future so for this purpose I’m looking at strictly a 5.56

I would be putting some type of break or flash hider, undecided, and a Surefire warden on it first. Later on I’m hopefully putting a can on it but that is less certain so I would like something that’s nice to shoot in the meanwhile.

Everything I read seems to say the 11.5/12.5 does everything a 10.5 can but better. I’m sure it does but there’s a big group of people that say 10.5 is the preferred setup.

Anybody have something like this that I could shoot and try out before I invest? I’ve never shot shorter than 14.5 so I don’t know what to expect really besides what I’ve researched. Willing to provide ammo or pay of course if my ammo isn’t the correct type. I’m in Mass.

I have two 12.5 uppers and my 12.5 FSB upper is my smoothest and most comfortable shooter (even more than my 14.5). I love my 10.3 DD MK18 barreled upper as well, but the 12.5 FSB upper has always been my favorite to shoot.

 

[Mass-diver]

I wish there were more 12.5s on the market as it seems like a really useful length.

I recently purchased this 11.5 BCM lightweight that I am very happy with so far and I thought handled well in a carbine class.

And of course my old school commando build is a favorite.

 

[Grendizer138]

10.5” or what’s the point?

 

[xtry51]

10.5 or shorter. We have some 7.5" pistols the kids learned to shoot with.

Yes you lose velocity, but you gain weight savings and maneuverability, while maintaining controls, shared ammo and magazines.

My only other recommendation would be a 9mm AR platform in <10". You then get heavier bullets and there are Glock mag variants to maintain commonality of ammo/mags.

 

[Compooky]

Exactly what do you mean when you say "MK 18 style"? Is that like using a RIS II rail with a mix of whatever for everything else?

 

[Da_lucche]

I wish there were more 12.5s on the market as it seems like a really useful length.

I recently purchased this 11.5 BCM lightweight that I am very happy with so far and I thought handled well in a carbine class.

And of course my old school commando build is a favorite.

View attachment 691763View attachment 691764

I had a spare Black Hole Weaponry/Crusader Arms 16" M4 Profile cut down to 12.5 by Adco. The chop and thread ended right before the first cut in the barrel, so it worked out perfectly.

10.5” or what’s the point?

Get both.

10.5 or shorter. We have some 7.5" pistols the kids learned to shoot with.

Yes you lose velocity, but you gain weight savings and maneuverability, while maintaining controls, shared ammo and magazines.

My only other recommendation would be a 9mm AR platform in <10". You then get heavier bullets and there are Glock mag variants to maintain commonality of ammo/mags.

I had a 7.5" upper for a brief period of time. Never had any issues with it. Was actually a really soft shooter for the barrel length. Had a KX3 on it so that probably helped.

Exactly what do you mean when you say "MK 18 style"? Is that like using a RIS II rail with a mix of whatever for everything else?

yea, he probably means he isn't worried about creating a clone correct of version of a CQBR/MK18/MOD 0/1 upper.

 

[bondsman333]

Do you ever plan on sticking a can on it?

If not go 11.5" or more.

I have a true MK18 upper from DD and its great. I have a hodge podge of parts in 10.5" and its less reliable (DD alters the gas port on the barrel).
My favorite rifle is 11.5" BCM.

 

[DW357]

10.5” or what’s the point?

This.

I love my 10.5" 5.56 and 7.62x39 upper.

 

[SJan]

10.5, because it's a SHORT barreled rifle...

A quality barrel and adjustable gas block will negate any reliability concerns vs 11.5 or 12.5.
The flash, noise, or unpleasantness will be affected more by your choice of ammunition and muzzle device than that 2" of barrel.

 

[JenkkiMike]

No option for 9.3"? Yeah I know it doesn't make the most sense from a ballistics standpoint but it sure is fun and cheaper than an actual Krink.

 

[appraiser]

just because the topic interests me as far as the ballistics go, what weight bullet would one use in different SBR lengths and what twist rate for that weight?

 

[Da_lucche]

just because the topic interests me as far as the ballistics go, what weight bullet would one use in different SBR lengths and what twist rate for that weight?

I think popular opinion is 75/77 grain is optimal in 1/7 twist 10.3/10.5 barrels. Personal experience is that I have had no issue with using 55 grain out to 100 yards with my 10.3. My 12.5 FSB is a 1/9, so I use 55 grain for both target and defense ammo, but 12.5 in a 1/9 should be totally fine with 68 grain and under. Others will correct me if I am wrong.

 

[OJ didnt do it]

I have two 12.5 uppers and my 12.5 FSB upper is my smoothest and most comfortable shooter (even more than my 14.5). I love my 10.3 DD MK18 barreled upper as well, but the 12.5 FSB upper has always been my favorite to shoot.

What brand/model is your 12.5? I’m very partial to the pinned FSB

 

[OJ didnt do it]

I wish there were more 12.5s on the market as it seems like a really useful length.

I recently purchased this 11.5 BCM lightweight that I am very happy with so far and I thought handled well in a carbine class.

And of course my old school commando build is a favorite.

View attachment 691763View attachment 691764

I would love a BCM 11.5 with a pinned FSB but they seem to be sold out on all the common places. Great looking setups man.

 

[OJ didnt do it]

Exactly what do you mean when you say "MK 18 style"? Is that like using a RIS II rail with a mix of whatever for everything else?

I intend on throwing a spare KAC RAS on it and I like vertical grips so I’d buy a broom handle. I like pinned FSB as they had on the original MK18s (please correct me if I’m wrong). I’d like to get something “higher end”, it doesn’t HAVE to be DD, im open to colt, LMT, BCM.

 

[OJ didnt do it]

I think popular opinion is 75/77 grain is optimal in 1/7 twist 10.3/10.5 barrels. Personal experience is that I have had no issue with using 55 grain out to 100 yards with my 10.3. My 12.5 FSB is a 1/9, so I use 55 grain for both target and defense ammo, but 12.5 in a 1/9 should be totally fine with 68 grain and under. Others will correct me if I am wrong.

It was recommended to me that I try out Hornady 75Gr which I guess they made specifically for SBRs.

 

[Bt74]

I have a 7" PSA Marauder pistol that is a blast to shoot! Throws a nice fireball, and pisses off the Fudds at the range at the same time!

 

[Caveman]

All of them! All suppressed!

 

[MaverickNH]

Shorter Barreled Rifle - just file a bit off the end...or go 10.5 for a Short Barreled Rifle. If you don't need it as short as it can function, you don't need a SBR

 

[Compooky]

Just buy a LMT 10.5 barreled upper while it's still on sale now. Stick the handguard and brake on it then put it on your lower of choice and call it a day.

Should be easy to find someone in whatever part of Mass you're in with SBRs to try out .

 

[larueminati]

If you care about ballistics get the 12.5

 

[PappyM3]

It’s all a trade space. They’ll all work in tight quarters. They’ll all put bad guys down out to a few hundred yards. Just preference.

10.x” will have a faster maintenance cycle and has a sharper drop in velocity compared to the drop from 12.5 to 11.5. But if you want as short as possible, it’s your bag for 5.56.

11.5 gets you 40% more dwell time than 10.5, with only 4% longer overall length. Plus a bump in velocity.

12.5 gets you more velocity, obviously, and depending on the ammo, it can get you closer in velocity to 14.5” than to 11.5”. But 12.5” also allows you to start using a mid-length gas system. You might be able to do that with 11.5” and a silencer.

They’re all loud indoors though. I wouldn’t base your decision on noise.
11.5” is a good middle ground that balances length, velocity, and maintenance. And I think 12.5” is a great general purpose carbine length if you don’t have a longer upper too.

But if you want to do a Mk18-ish, then you need to go 10.3/5. Cloners will get upset if you don’t do a 10.3”, but whatever.

 

[OJ didnt do it]

It’s all a trade space. They’ll all work in tight quarters. They’ll all put bad guys down out to a few hundred yards. Just preference.

10.x” will have a faster maintenance cycle and has a sharper drop in velocity compared to the drop from 12.5 to 11.5. But if you want as short as possible, it’s your bag for 5.56.

11.5 gets you 40% more dwell time than 10.5, with only 4% longer overall length. Plus a bump in velocity.

12.5 gets you more velocity, obviously, and depending on the ammo, it can get you closer in velocity to 14.5” than to 11.5”. But 12.5” also allows you to start using a mid-length gas system. You might be able to do that with 11.5” and a silencer.

They’re all loud indoors though. I wouldn’t base your decision on noise.
11.5” is a good middle ground that balances length, velocity, and maintenance. And I think 12.5” is a great general purpose carbine length if you don’t have a longer upper too.

But if you want to do a Mk18-ish, then you need to go 10.3/5. Cloners will get upset if you don’t do a 10.3”, but whatever.

I was really hoping for a 11.5” and I’m hoping in the future I’ll be able to find one. For now I went with the LMT 10.5” (bUt iTs nOt cLoNe CoRrEcT) as they’re on sale for a very fair price.

Time to order some other parts and get the paperwork cooking.

 

[OJ didnt do it]

I was really hoping for a 11.5” and I’m hoping in the future I’ll be able to find one. For now I went with the LMT 10.5” (bUt iTs nOt cLoNe CoRrEcT) as they’re on sale for a very fair price.

Time to order some other parts and get the paperwork cooking.

View: https://m.youtube.com/watch?v=blljOiEtHec



Fat chance as it hasn’t been touched since September but I like the thumbnail

 

[42!]

I've got a 5.56 (well actually a 223 wylde) SBR in 10.5, very manageable, not too much flash. Some of this might be the BRN180 upper, I don't have a short AR15 upper to compare it to.

You'll need to post a location if you want anyone to try out what they have, can't take an SBR over state lines without getting permission from the ATF. And any built in NH probably have too many scary features for MA.

 

[MGnoob]

You never stated what the purpose of the rifle is.
Ill assume it’s not for distance. So I’d say 7.5” , 10.5”… Without a suppressor I don’t even understand the point of your SBR..
So as a generic Massachusetts answer. I’d say 14.5 with a pin suppressor making you 16”

It’s not like you’re entering and exiting vehicles with a tactical roll.

If you’re gonna go short for the purpose of going short. 7.5” the way to go… Perfectly accurate out to 200 yds

 

[Bodhisattva]

Can or no can? Can, 11.5. No can, 12.5.

 

[42!]

You never stated what the purpose of the rifle is.
Ill assume it’s not for distance. So I’d say 7.5” , 10.5”… Without a suppressor I don’t even understand the point of your SBR..
So as a generic Massachusetts answer. I’d say 14.5 with a pin suppressor making you 16”

It’s not like you’re entering and exiting vehicles with a tactical roll.

If you’re gonna go short for the purpose of going short. 7.5” the way to go… Perfectly accurate out to 200 yds

assuming you didn't mean that