AR-15 (suppressed) SBR Length?

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AR-15 (suppressed) SBR Length?

10.5"
46
38%
11.5"
44
37%
12.5"
30
25%
 
Total votes: 120

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AR-15 (suppressed) SBR Length?

Post by 700PSS » Fri May 07, 2010 10:24 pm

Cutting back RRA 1/9 twist heavy barrel from 16". Plan to use 55gr.

Many respected opinions like all 3 lengths, but I need a clear winner. Feel free to offer reasons why your choice is best for you.
Last edited by 700PSS on Fri Jun 04, 2010 1:46 pm, edited 3 times in total.

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Post by continuity » Sat May 08, 2010 1:00 am

If you're gonna do it, make it as short as you can with the round still being effective.

2 cents worth.
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Post by chp5 » Sat May 08, 2010 8:32 am

My vote is 11.5.

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Post by Kramer » Sat May 08, 2010 3:34 pm

I voted for the 11.5 as well even though I have a 10.5 since that is what LWRC was selling at the time.

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Post by BISHOP » Sat May 08, 2010 6:06 pm

Since I own a 7.5, and AAC won't let me shoot the thing with their suppressor on it, I vote for the 10.5.
I LOVE the compactness of the 7.5 so the 10.5 would be the next best thing.


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Post by TypeR632 » Sat May 08, 2010 8:40 pm

It would be great if AAC or someone would make a takedown can just for a 7.5". I don't care if it's not as quiet as a M4-2000. Then if the baffles start eroding send it back and have the baffles replaced.
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Post by Chinerd » Sat May 08, 2010 9:55 pm

I have a 10.5 and love it. But you might get a little better accuracy with a 11.5

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Post by BWT » Sun May 09, 2010 11:18 am

Chinerd wrote:I have a 10.5 and love it. But you might get a little better accuracy with a 11.5
A little bit more fragmentation at range as well. (I don't know exactly how much, but, more fragmentation is more fragmentation.)

If I was building an SBR AR today, it would be an 11.5'' BCM.

I found that 12.5'' was getting too closer to 14.5'' and losing the real appeal (at least to me) of having an SBR.

Where I felt that 10.5'' was getting too short.

I'd go with 11.5'' these days, maybe 12.5'' if I for some reason couldn't get 11.5'', but I'd go for the longer barrel as a second choice if I couldn't get 11.5''.

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Post by dcmdon » Wed May 12, 2010 1:54 pm

continuity wrote:If you're gonna do it, make it as short as you can with the round still being effective.

2 cents worth.
If you want the round to still be effective, then leave it as a 16 and save yourself $200

I don't remember the exact numbers, but my 10.5" LMT SBR gives up a lot of muzzle velocity to a 16. You don't have to be shooting very far out before you reach a point where the .223 does not tumble and come apart.

Before anyone can INTELLIGENTLY recommend a length, you need to tell us what you want this gun for.

If its just a toy, then go as short as you dare.

If its going to be a suppressed toy, I wouldn't go shorter than 10.5. This is based on recommendations from a suppressor rep I spoke with.

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Post by -k- » Wed May 12, 2010 3:27 pm

Need more info on the intended use.

12.5" for an all around type carbine SBR.

10.5" if it's for compactness and will supplement a 14.5"/16" carbine.

To me the 11.5" is pretty much the red headed stepchild, unless you have a specific need like mounting an SPR-M4 etc. Reports of the 11.5" being so much more reliable than a 10.5" are based on low quality samples, wrong buffer, cut down without gas port work...

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Re: AR-15 SBR Length?

Post by BAYOU » Fri May 14, 2010 6:57 pm

I'm going over the same delima now, sent my paperwork off on a 10.5 before I decided to go with a SureFire FA556AR and now I'm limited to a 11.5 or 12.5. Do to the different mounts I'm only coming up with .5 difference between the two because of the mounts. Didn't want a 12.5 because I wanted a 10.5 or 11.5 but .5 isn't that much, 3.5 inches for $200.

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Re: AR-15 SBR Length?

Post by dcmdon » Fri May 14, 2010 10:03 pm

BAYOU wrote:I'm going over the same delima now, sent my paperwork off on a 10.5 before I decided to go with a SureFire FA556AR and now I'm limited to a 11.5 or 12.5. Do to the different mounts I'm only coming up with .5 difference between the two because of the mounts. Didn't want a 12.5 because I wanted a 10.5 or 11.5 but .5 isn't that much, 3.5 inches for $200.
What do you mean you "are limited". If you want to go shorter, send the ATF a letter certified telling them what you are doing, and you are done. You just need to notify. Not ask permission.

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Re: AR-15 SBR Length?

Post by BAYOU » Sat May 15, 2010 12:52 am

Limited because of the FA556AR can thought I purchased, not a big deal to go 11.5 but due to the different mounts for 11.5 and 12.5 its only a increase of .5. The FA556AR is a reflex style can, the barrell has to be atleast 11.5.

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Re: AR-15 SBR Length?

Post by dcmdon » Sat May 15, 2010 8:27 pm

I still don't get it.

is the gun longer or shorter than on your Form1?

Whatever it is, just send the ATF a letter informing them of the change. If you are going longer, you don't even need to send a letter.

Again, you are not asking permission, you are notifying.

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Re:

Post by chp5 » Sat May 15, 2010 11:00 pm

-k- wrote:Need more info on the intended use.

12.5" for an all around type carbine SBR.

To me the 11.5" is pretty much the red headed stepchild . . .
What is the advantage of a 12.5 over a 11.5?

I've read opinions - including opinions of the guys who own Bravo Company and Pat Rogers - that the 11.5 has better dwell time and better reliability over a 10.5. Please explain your reasoning for your statement. BTW - I'm not trying to prove a point or argue with you. You obviously have industry experience - just interested in your reasoning. Thanks!

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Re: AR-15 SBR Length?

Post by BAYOU » Sun May 16, 2010 12:49 am

I understand that I'm not asking permission but I'm simply stating the difference between a 11.5 and 12.5 with a FA556AR. I realize that I will need to notify the NTF but I was just speaking of the diiference of a 11.5 and a 12.5 due to the adapter for a FA556AR

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Re: AR-15 SBR Length?

Post by dcmdon » Sun May 16, 2010 10:26 am

is the adaptor going to be welded on?

Also, from my understanding, if the form 1 has a certain length, and you lengthen the gun, you don't have to do anything. You only have to communicate if you shorten the gun.
Please don't take this as truth, check with the ATF. But thats what I have been told.

Don

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Re: AR-15 SBR Length?

Post by chingon » Sun May 16, 2010 6:36 pm

I SBR'd a Professional Ordnance 7.5'' pistol
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Re: AR-15 SBR Length?

Post by dcmdon » Sun May 16, 2010 8:18 pm

I was asking about Bayou's post. its pretty hard to understand. Like he typed it on a blackberry durring an earthquake.

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Re: AR-15 SBR Length?

Post by -k- » Mon May 17, 2010 11:34 am

BAYOU is dealing with what barrel length will allow mounting his reflex can.
If you use a 1" long gas block/Switchblock and a 7"-8" rail you can mount the 556AR on an 11.5" barrel without the 203 mount.



As to the 11.5". Testing on the MK18 (10.3")show reliability and service life very close to a 14.5" M4.
The longer the barrel the more you can get away with things like inferior carbine buffers, worn out springs and sub standard ammo.
Last edited by -k- on Fri May 21, 2010 10:49 am, edited 1 time in total.

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Re: AR-15 SBR Length?

Post by BISHOP » Thu May 20, 2010 10:51 pm

Image
My 7.5 is a PWA lower with a M1S pistol kit.
Nothing is left from that kit but the barrel, handguard and front sight.
Every year I put another accessory on it that isn't too ugly, but more utilitarian.
It currently sports the Magpul pistol grip with spare bolt and fireing pin unit, a MS1 sling and a loop plate on the stock for the sling to attach to.


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Re: AR-15 SBR Length?

Post by BWT » Sun May 23, 2010 2:24 pm

http://www.ar15.com/forums/topic.html?b ... 764&page=2

I don't know SBR's, don't pretend to.
Q: Why BCM chose the 11.5" SBR over the 10.5"

I get this question a lot. It is a good one. When we spec our program we can build anything we would like, so we sat down and looked at the pros and cons.

First Statement: I know a good 10.5" SBR can run very well. I personally own a semi MK18 type and it runs great. No problems.

A: Dwell time.
Dwell time is the time that your gas operated weapon maintains pressure to continue the cycling of the weapon. It primarily exsists from the time the bullet passes the gas port in the barrel to the time the bullet exits the muzzle. When you pull the trigger and fire the weapon the movement of the bolt carrier group unlocks the bolt, extracts, and ejects the spent casing. Then it cocks the weapon, feeds, chambers the next round, and then locks again. One of the thing that can make SBRs finicky is the dwell time (or lack of).

The 11.5" carbine is approximately 4% longer weapon than its' 10.5" counterpart, but this extra inch gives the barrel a 40% increase in length for dwell time. IMHO, this is an excellent trade off. This additional dwell time (all other things being equal) will allow the carbine to be more forgiving to different ammo types, extremes in air temperature, weak or worn extractor springs, worn extractors, buffer weights, etc.

Last Statement: For those folks who have a 10.5" that works very well, I would reply; me too. (see first statement)

If I had to "go to war" with a AR15 Carbine, I would grab the BCM 11.5".
The BCM 11.5" Runs Like a Dream.

Hope this info helps,
Paul
Originally Posted By kap_x:
Originally Posted By Croft32:
Originally Posted By Mopseydocks6014:
What advantages would the 12.5 have over the 11.5 if any??


More dwell time (not sure how significant it is in regard to reliability), ability to mount certain cans that wont fit on the 11.5", more velocity to shoot a little further, and, of course....more weight!

Not sure if 12.5 will give much benefit over 11.5 in regards to dwell time.
There's no marking on the graph, or dedicated line for 12.5" in the table, but you can kinda rough your own

http://ar15barrels.com/tech/pressure-time.gif


12.5" would give about .148 net time. Nice compared to a mid length 14.5" at .139 net time.
Can you put dwell time into perspective for us? The significance of it?

I'm curious, and genuinely ignorant, is more dwell time a good thing or bad thing?

I get the impression more is better, especially as you look at the longer gas lengths, the longer dwell times are the more reliable systems, typically.

At what point is it 'Good" or "Bad"?

What's the most desirable?

Thank you.

I'm asking for two reasons

A) I'm finishing up my Mid Length BCM AR (I don't have enough of it done really to post pics, but we're close) I've shot over a hundred rounds through it, just because I couldn't wait any longer. :lol: But that's hardly any kind of real test of reliability. (110 rounds at a pistol range with no rear BUIS... I felt pretty tacticool, but it was done... I lasted a little over 24 hours before I broke down and had to shoot the newness off of it.) and I'm considering an SBR down the road.

B) I also like to shoot Wolf, because it's cheap, as you can see illustrated in the above section A), I'm a broke college student, I shoot wolf, and I can't afford a BUIS yet. :lol: But, how tolerant are SBR's of lower powered .223 rem used for practice?

I know rob_s advocates wolf ammo and he shoots it through a 6933 he has (11.5'' Colt SBR), but I'd like a bit more info, and I figure for posterity, it'd be great if we could get an explanation, maybe educate us more for what to look for. Thanks.

I voted for 11.5'' SBR AR's... which is what I thought I would want, but I'm torn between that and a 12.5'' SBR, way down the road.

Thanks in advance.

ETA: I was thinking about it, since this is also a forum that obviously likes suppressed AR's, I'm guessing 12.5'' might be best, because that dwell time is only going to decrease, speeding up bolt speed when suppressed, whether it be in a 10.5'', 11.5'' or 12.5''.

Do you have any statistical figures to explain the difference between 10.5'', 11.5'' and 12.5''?

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Re: AR-15 SBR Length?

Post by misfit762 » Sun May 23, 2010 11:03 pm

Currently saving for the Noveske 12.5. Shoots more accurate than my issued M4 at 14.
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Re: AR-15 SBR Length?

Post by BWT » Mon May 24, 2010 12:45 am

misfit762 wrote:Currently saving for the Noveske 12.5. Shoots more accurate than my issued M4 at 14.
Are you the only one that's maintained that M4? (Just trying to get an idea of kind of care it's received... people do stupid things to guns, especially when they don't pay for them, I.E., issued weapons... had a friend shoot his M249 in training purposefully to get the barrel to glow, just saying)

Was the Novekse you shot Stainless Steel? I know their Crusader models are Stainless Steel.

Most of my questions are pertaining to reliability and the flexibility and which would serve best.

But I do appreciate the info, Noveske puts out quality, without a doubt.

I appreciate any info, honestly, I also think it'd be good for posterity.

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Re: AR-15 SBR Length?

Post by misfit762 » Mon May 24, 2010 1:01 am

BWT wrote:
misfit762 wrote:Currently saving for the Noveske 12.5. Shoots more accurate than my issued M4 at 14.
Are you the only one that's maintained that M4? (Just trying to get an idea of kind of care it's received... people do stupid things to guns, especially when they don't pay for them, I.E., issued weapons... had a friend shoot his M249 in training purposefully to get the barrel to glow, just saying)

Was the Novekse you shot Stainless Steel? I know their Crusader models are Stainless Steel.

Most of my questions are pertaining to reliability and the flexibility and which would serve best.

But I do appreciate the info, Noveske puts out quality, without a doubt.

I appreciate any info, honestly, I also think it'd be good for posterity.
I do take care of my M4. My life depends on it. I make sure my Soldiers take care of their weapons. During a fire fight in Afghanistan, my Soldier's M249 was the only one that fired through the whole fight.

I have not had the pleasure of shooting a Noveske yet. From what I've read and heard the issued M4 shoots at 3MOA. The Noveske shoots much better, around 1MOA I believe. The Stainless Crusader is the one I want.

I hope this helps. I'm sure someone on this site can provide better info than I can.
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