Discussion of how to get an 8.5" Barrel SBR AR15 to 29" OAL

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  • Hawkeye

    The Leatherstocking
    Jan 29, 2009
    3,971
    Hi everyone:

    This thread is meant as a place to discuss a topic that came up here, on page three:

    http://www.mdshooters.com/showthread.php?t=145142

    Maryland law (or, at least the MSP's current interpretation of Maryland law, which many of us believe to be in error and which Engage Armament is currently suing them over) says that all newly made SBRs in Maryland must have an OAL of at least 29", measured from the end of the fully extended buttstock to the tip of the barrel, not counting any non-permanently attached muzzle devices. If the OAL is not at least 29", the SBR is considered a "copycat" weapon and is banned.

    Currently, this leaves many people just using a 10.5" barrel in order to make the 29" OAL. However, some rounds, particularly .300BLK, function optimally out of an 8.5" or so barrel, and many of us would like to have SBRs built around that barrel length.

    In the other thread, several of us were discussing ways that we could use certain parts or combinations of parts in order to get an 8.5" barreled AR15 SBR to meet the 29" OAL rule. This thread is for a clear discussion of that topic so it will easily be found in the future.
     

    Wayne1one

    gun aficionado
    Feb 13, 2011
    3,127
    Bowie, MD
    This has been discussed at length in other threads. Magpul ACS-L stock with enhanced butt pad and standard flash hider (pinned) will get you there. Or you can use Vltor A5 extension tube with same stock & but pad, no pinning necessary. No need for a dedicated thread......

    Sent from my VS990 using Tapatalk
     

    Hawkeye

    The Leatherstocking
    Jan 29, 2009
    3,971
    Ok.

    Some of us were discussing measurements of various parts in the other thread. I took a tape measure to some of my rifles, and here's what I came up with:

    I have one Rock River AR with a commercial spec 6 position buffer tube (my first AR from years ago) that has a 16" barrel. According to my measurements, with the basic M4carbine stock fully extended, the OAL is right around 34 and 7/8". LOP is about 14 and 1/4".

    I have one homebuilt AR (billet Adcor lower, billet Cross Machine upper) with a 5 position VLTOR milspec tube and a VLTOR eMod stock. OAL with the stock fully extended is right around 35 and 1/2". LOP is closer to 14 and 3/4".

    So... if we subtract 7.5" from all of these measurements to theoretically convert the 16" barrels into 8.5" barrels, we would be left with:

    Rock River OAL 27 and 2/8"
    Adcor OAL 28"

    Some of the solutions we discussed were:

    VLTOR A5 7 position buffer tube. This is claimed to add about 3/4" to the OAL.

    LAW folding stock adapter. This adds 1.3" to the OAL, BUT we would then have to be careful about the other "evil features" on the rifle. A rifle with both a folding stock and a flash hider is illegal as a copycat, so this would preclude using a suppressor or flash hider.

    Adding a thicker buttpad to the stock. This would add varying amounts of OAL.

    Doing some theorizing....

    If you had an SBR with an 8.5" barrel and a VLTOR eMod on it (like my current rifle, but a shorter barrel) and a standard 5 position buffer tube on it, you'd have an OAL of about 28". If you added the 7 position A5 tube to that, you'd be at about 28 and 3/4". Adding a slightly thicker buttpad would get you past 29".
     
    Last edited:

    Hawkeye

    The Leatherstocking
    Jan 29, 2009
    3,971
    Sorry, you guys posted while I was typing and went outside to help my neighbor with the oil in his car. Anyhow...

    A combination of pinned muzzle device, Magpul ASC-L or similar length stock, and a thicker recoil pad should do it.

    I don't want to pin a muzzle device. It kills the ability to add different options to the rifle for suppression and the like.

    This has been discussed at length in other threads. ... No need for a dedicated thread......

    Yes, but as I discussed above it's not always easy to find. Having this thread here with a searchable title will hopefully help others find this information.

    Magpul ACS-L stock with enhanced butt pad and standard flash hider (pinned) will get you there. Or you can use Vltor A5 extension tube with same stock & but pad, no pinning necessary.

    Ok... so without pinning we're looking at the A5 tube and a long stock with an extended buttpad.

    Does anyone have a length comparison between the ACS-L and the VLTOR eMod or other stocks? I'm Googling around but having trouble finding a definite comparison. I'm personally partial to the VLTOR, but I think it'll be about 1/8" short.
     

    Wayne1one

    gun aficionado
    Feb 13, 2011
    3,127
    Bowie, MD
    ACS-L is 7.95" plus another .70" with enhanced butt pad (according to Magpul)

    ACS-L, Mil-Spec (stock configuration)
    Weight: 0.78 lb.
    Weight, w/ Rec. Extension: 1.02 lb.
    Length, Maximum: 7.95 in.
    Width, Maximum: 2.17 in.
    LOP Adjustment Range: 3.25 in.
    LOP, M4 Collapsed: 11.75 in.
    LOP, M4 Extended: 15.00 in.

    Vltor Emod is 7.75" (according to Vltor)

    Length with buttpad: 7.75 inches (at centerline of tube)
    Weight: 14 oz
    LOP fully collapsed: 11.50 inches
    LOP fully extended: 15.00 inches
    Buttpad angle: -5 degrees with decrease to -15 at toe
    Receiver extension is made of 7075 T6 impact extrusion
     

    frogman68

    товарищ плачевная
    Apr 7, 2013
    8,774
    Took the flash suppressor off my 8.5 inch barrel (hardened arms if it matters) from the tip to the end of the lower is 15 7/8 so its 13 1/8 will be the winner
     

    Pinecone

    Ultimate Member
    MDS Supporter
    Feb 4, 2013
    28,175
    I don't want to pin a muzzle device. It kills the ability to add different options to the rifle for suppression and the like.

    I would use a ThunderBeast Flash Suppressor/suppressor mount.

    I would prefer to not pin/weld, but to shorten the rifle by another 2" would be nice.

    Of course, a 9" barrel would not be too bad, and would be right in the range.

    BTW, what do you have to do to amend a Form 1 for a shorter barrel??? :)
     

    Hawkeye

    The Leatherstocking
    Jan 29, 2009
    3,971
    BTW, what do you have to do to amend a Form 1 for a shorter barrel??? :)

    I do not believe so. The Form 1 is initially filled out with the OAL of the firearm when it is made. You are then later free to reconfigure it to other lengths or whatever as long as you stay otherwise legal. The ATF has asked that they be notified of any permanent changes to the length so that they can update the NFA database, but you're not obliged to notify them as long as you can return it to the original configuration (and maybe not even if you can't, I don't actually remember).
     

    pwoolford

    AR15's make me :-)
    Jan 3, 2012
    4,186
    White Marsh
    I would use a ThunderBeast Flash Suppressor/suppressor mount.

    I would prefer to not pin/weld, but to shorten the rifle by another 2" would be nice.

    Of course, a 9" barrel would not be too bad, and would be right in the range.

    BTW, what do you have to do to amend a Form 1 for a shorter barrel??? :)

    :thumbsup: Bingo

    Though if MSP starts carrying tape measures to ranges you could run into problems.
     

    pwoolford

    AR15's make me :-)
    Jan 3, 2012
    4,186
    White Marsh
    When I get time I'll try to shuffle some of my shorter uppers around and record the measurements. Luckily almost all of my SBR lowers are pre 2013 so I don't have to deal with MSP's ridiculous 29" rule.
     

    screamingeagle

    Active Member
    Mar 7, 2010
    507
    Sorry ran out of time to post these last night.

    Here us my LWRC 8.5 first pic is with the Magpul stock with .70 thickest pad,with the VLTOR 7 position buffer tube.

    Makes 29 inches but have to measure from angled portion of the buttpad where it extends the furthest.

    Th second stock is the one that comes with the VLTOR. It measures 29 also from the furthest angled portion of the buttpad.
     

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