I am starting a build and was wanting to use a 10.3" Daniel Defense Barrel. I am going to put a can on it eventually and was leaning toward the AAC M4-200, but I have heard good things about the AAC SPR/M4 recently. It is my understanding that the SPR/M4 won't fit on a 10.5" barrel because of the MITER mount that it uses (overhangs the barrel so far that it is obstructed by the gas block). I am not sure how long the barrel would have to be to use the SPR/M4, can anyone give me a definitive answer? This is some info I got from the AAC website:



                         Overall Length   Length Added   Weight (ounces)
AAC-M4 2000          6.625"                 5.100"                 17.10
M4 2000 Mount        2.500"                 1.875"                   4.35

AAC-SPR/M4          8.265"                  4.900"                  18.00
SPR/M4 Mount        4.250"                  1.750"                    4.25


Given the overall length and length added some simple math will give us a "length of barrel overhang" for each unit of:

AAC-M4 2000     1.525"
M4 2000 Mount     .625"

SPR/M4                3.725"
SPR/M4 Mount     2.500"

I guess I have two questions. #1 is a cold hard fact and #2 is your opinion.

1. What is the minimum barrel length required for the SPR/M4?
2. Is this increase in barrel length and resulting increase in overall weapon length and weight worth the benefits gained by the SPR/M4 can?

You need about 2.5" of clearance in front of the gas block to use the SPR/M4. The M41000 or the M42000's would be a great choice. Just depends on how much you want to spend.

I have an M4-2000 and use it on several 11.5" ARs.  I have no complaints.

You already answered the question of SPR/M4 suppressors and barrel length.  The SPR/M4 is a nice suppressor.  It will reduce gas blowback to the shooter more than the M42K does.  But you'll need a longer barrel.

Mark

Just to point something out, AAC warranties their suppressors on bbls as short as 10.5", so the 10.3 may leave you high and dry should there be an issue.

I'd just get the M42K. Seems to be their premier suppressor.

+1 on the M42K

They say 10" is the shortest.

http://www.silencertalk.com/forum/viewtopic.php?f=86&t=58100

But the longer the barrel...the longer the suppressor life.........

A brake has been recommended for shorter barrels lately.

Gotcha. Thanks for the clarification.

A brake is definitely a good idea.  Acts as a sacrificial baffle.  Someone had posted pics of their AAC brake after putting a few hundred rounds through it on a 10.5 barrel and there was a lot of corrosion for such a small round count on it.

Might I suggest an 11.5" barrel instead of the 10.3"?  It will increase the life of your can and will get a lot more velocity for just 1" of barrel (at least 100fps iirc).  Also, for the reasons Bravo Company states here.

eta:  M4-2k ftw

I really like the SPR/M4 on my 12.5" N4.

Here is some chrono data from three different weapons to illustrate the velocity increase between 11.75 and 12.5; we didn't have a 10.5 to try that day:

I agree - a brake is a great idea.  I have an AAC "brakeout" on my 12.5" SBR and an AAC M4-2000
Without the suppressor affixed the brake is stooopid loud and has Hollywood quality muzzle flash.
With the can in place, it's perfectly well mannered.

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another vote for the m4-2000. i am running the brake on my 6933 and its very loud without the suppressor but after only 200 or so rounds i can already see the erosion around the brake baffles like others have posted pics of.

Where did you get a 12.5 N4?  The silly SS barrel on mine is so much heavier than I need.  

OP your stuck with a M42000 unless you get a 12.5 barrel.  I really like the config, its as long as my 16" with SPR/M4 mount.  Compared to the 10.5 M4/2k config, you get significantly more barrel, with the velocity and reliability that implies, and its the same overall length.  Its just 2" longer with no can.  If you arent married to that barrel, get a BCM 12.5 or Noveske in whatever config you like.  Mine has a switchblock set back in the SWS Noveske rail.  You'll be happy with the 10.3/M42k though, if thats the route you want to go.  

(I'm running a SPR/M4 on a 12.5, just some food for thought for you)

I'm in process of SBRing a scar. I wish AAC would make a brake for the SPR/M4 can.

The 12.5" N4 came from a "special" run that Noveske did for MSTN; it is a real nice shooter, and the balance is great.  My wife has a 16" middy N4 which also shoots very well.  To round out our Noveske/MSTN triad, we have a 12.5" 6.8 SS Noveske, that shoots MOA and makes 2900 FPS using SSA 85 TSX TL's.  

Mandatory arfcom gratuitous porn:



For the OP, an SPR/M4 will work on an 11.5 if you use a short [length] gas block, but you won't be able to use a 9" handguard.

A 12.5 Noveske with the SPR/M4 is hard to beat!  

Dang, an extra 200fps outta the Operator verse the LWRC barrel w/ m193?  That's impressive!

I really like my M4-2000.  A Break or Breakout is a must for the short barrel AR's and a can.  Here is a pic of my Breakout at 200 rounds.



Here it is at about 1000 rounds.  Note the coning.



Here is the can with about 200 rounds through it.  Kind of hard to see, but there is no pitting at all.


Here is the gun. (10.5" Noveske)  The whole  thing with can on is still shorter than a standard 16" AR.   It is real nice to shoot too.  5.56 is not a quiet round, but the M4-2000 really does it't job well.  A 12.5" will give you better balistics and down range energy, but I really like the size and overall feel of a 10.5" AR.  Even with adding a can, it still feels great.   A 12.5" barrel with SPR M4 will be only 1" longer, but no break and heaver.



Jeremy

M4-2000, just make sure you get the breakout or the brake mount.

3000 rounds on a 10.5" barrel:

Jeez, that is nuts! How often do you shoot your 10.5 without the can?

About 99% with the suppressor on.

Do you have any pics?

 

heres a pic i just took. this is after about 200 +/- of  american eagle xm-193 100 round packs.

Looks like it will last at least 6000 rounds. That's a good value.



 

I'm really happy with it, when it wears through I'll just put a new one on and save the old one for a training aid.
The speed of the erosion has really slowed down, I bet it will easily go to the 10k mark if I can afford to shoot it that much.
It seemed like the initial 1.5k rounds did the most noticeable damage, but it has slowed down since the impact area opened up.

The biggest thing is the brake is preventing this from happening to my suppressor baffles.