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Gunsmithing SureFire SFMB 762-5/8-24 brake/supressor mount

LRI

Lance Criminal
Full Member
Minuteman
  • Mar 14, 2010
    6,314
    7,427
    52
    Sturgis, S. Dakota
    www.longriflesinc.com
    I'm stuck.

    I've got a barrel and I have a brake. After installing literally hundreds of muzzle brakes one would think this would be a no brainer.

    The part is a SureFire SFMB-762-5/8-24. On page 11 of the little manual that comes with the brake there's a generic print and a series of models listed in a table with various dimensions applied. -That part is easy, I got it.

    What's left to sort out is if this particular brake is actually listed in this chart. In the remarks column it lists "XX" as having an "MB" prefix in the part number. This brake has that prefix, but it also has an "SF" superseding it.

    It makes no reference to this particular/specific part#.

    The barrel is big. Bigger in OD than the brake is. I know SF cans often require a clearance on the backside of the brake so that the lock mechanism has the required room to do its job.

    I don't have a can to marry up to it and every time I've called SF to ask for guidance on this I get a very vague "broad sweeping" response. -leaving me feeling less than enchanted.

    In the past shit like this has resulted in some rather awkward conversations with customers because they get their stuff and it doesn't work. Cans don't fit, etc. Its really aggravating as I've devoted a pile of time with the tech support folks at SF and went at it assuming I'd done it right based on what they tell me. Obviously somewhere there's a disconnect. Either I'm explaining myself very poorly, or I'm not talking to the right person.

    SO if someone here has this SPECIFIC brake installed on a heavy barreled bolt gun along with a SOCOM series can I would be eternally grateful if you could post a photo or two detailing how the barrel contour looks behind the brake.

    I'll take my licks, call me a moron, whatever. Don't care. I just don't want to get my ass chewed by a customer again for this.

    Appreciate the help.

    C.
     
    Re: SureFire SFMB 762-5/8-24 brake/supressor mount

    Last I knew, Surefire had 2 brakes/mounts with different Inside Diameters.

    If the largest one still is not big enough, then you will have to turn the barrel down so that the brake/mount slides over. Are you stuck on the Surefire brake/mount because there will be a Surefire Suppressor installed?

    If the OD of the Surefire brake/mount is anywhere near the diameter of your barrel, then you have another problem all together and you will have to find a different brake.
     
    Re: SureFire SFMB 762-5/8-24 brake/supressor mount

    Chad, you have to contour the barrel to .775" for 2.75" back from the muzzle, here are some pics from my SureFire MB762SSAL RE Muzzle Brake which I'm pretty sure is the same demisions as the SOCOM when you are talking about the barrel profile. Also I sent you a PM about a barrel job. Thanks

    PS, IF YOU NEED ADDITIONAL INFO, contact "chucky" here on the hide, he's the Eastern NC SF rep.

    image-5_zps301be11a.jpg

    image-5_zpsf764cb5b.jpg
     
    Re: SureFire SFMB 762-5/8-24 brake/supressor mount

    The customer probably already has a suppressor for his SR25/AR10. I think what Chad is asking for is how much clearance he would need behind the brake because the muzzle diameter will need to be turned down or chamfered for clearance for the can. You boys get your Surefire SOCOM out and measure.

    ^^^ there it is.
     
    Re: SureFire SFMB 762-5/8-24 brake/supressor mount

    1/4" between the back of the brake and where the barrel resumes its normal contour should work with a MTU Contour or smaller, as long as the barrel has been contoured .775 for 2.75" from muzzle.
     
    Re: SureFire SFMB 762-5/8-24 brake/supressor mount

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Special Delivery</div><div class="ubbcode-body">1/4" between the back of the brake and where the barrel resumes its normal contour should work with a MTU Contour or smaller, as long as the barrel has been contoured .775 for 2.75" from muzzle. </div></div>


    Thank you. We'll give it a go! Much appreciated.
     
    Re: SureFire SFMB 762-5/8-24 brake/supressor mount

    -UPDATE:

    In spite of this pending winter storm warning were facing, the heavens opened, the clouds parted, and a little ray of sunlight shined on my fat ugly face.

    "Chuck" from Surefire stumbled onto this post and was kind enough to give me a call. Sorry germs, all you guys were wrong and I'd of installed yet another brake incorrectly.

    The SFMB-762-5/8-24 goes on like this:

    Turn a cylinder to an OD appropiate for 5/8-24 2A dimension.
    Cylinder length should be .625 from muzzle to shoulder.
    Thread to a 2A thread pitch diameter.
    The full thread form needs to be within .100" from the shoulder. Otherwise the brake gets pinched from the thread getting shallower and it fails to clam up against the shoulder.
    Install and time the brake accordingly.

    That's it. This brake has a projection on the back of the shoulder that serves as the standoff. This eliminates the need to turn back the barrel OD/shoulder depth qualified off the crown.

    What was explained to me (and it makes total sense) is that SF customer service center is located in CA. Due to the state's legal restrictions on guns typically fitted with these kinds of products the guys on the phone just don't have a great deal of hands on experience with them. Chuck however is not in CA and has a personal inventory of guns fitted with all sorts of SF wigits.

    I'll toss this out there: If your a known smith and ever need help with this stuff, gimme a call and I'll provide you with Chuck's contact information. He was very helpful and committed to ensuring I got good information.

    C.
     
    Re: SureFire SFMB 762-5/8-24 brake/supressor mount

    Chad, the new Surefire SOCOM Adapter must be very different from their old line, I was told they were the same except for the deminsions on the OUSTIDE of the brake giving it a different way of mating with the suppressor. SORRY FOR THE WRONG INFO, Chuck is GTG and I'm glad he called you before you used my info.
     
    Re: SureFire SFMB 762-5/8-24 brake/supressor mount

    surefire was less than helpful a few years back when i first installed one. this drawing has since been posted on this site a few times.

    Surefirematrix.jpg
     
    Re: SureFire SFMB 762-5/8-24 brake/supressor mount

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: excaliber</div><div class="ubbcode-body">Surefire is very hard to deal with. I have been waiting almost a year for 3 90T ratchets. There is no reason waiting that long. This is my last time with them! </div></div>

    Surefire doesn't make a 90T mount, you sure you don't mean AAC?
     
    Re: SureFire SFMB 762-5/8-24 brake/supressor mount

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: excaliber</div><div class="ubbcode-body">Surefire is very hard to deal with. I have been waiting almost a year for 3 90T ratchets. There is no reason waiting that long. This is my last time with them! </div></div>

    No offense but that is not SureFire that makes that adapter.