BCM Rail Clearance Issue

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  • masterdekoy

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    Feb 12, 2013
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    I have a BCM MCMR on a 300 blackout pistol build. The low pro gas block doesn’t give enough clearance for the MLok AFG I am trying to install. I’m able to get one set screw in but the other doesn’t fit. Is anyone aware of a low profile mounting solution for the inside of the rail? The stock MLok nut is too thick.

    Ive already ground down the screw so it doesn’t protrude.
     

    seedubs1

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    What LPGB? Can you swap it for one with less material on the underside? Go to a taper pin one? Is there extra material under the LPGB that can be removed?
     

    MCgrease08

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    Mar 14, 2013
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    Earth
    I have a BCM MCMR on a 300 blackout pistol build. The low pro gas block doesn’t give enough clearance for the MLok AFG I am trying to install. I’m able to get one set screw in but the other doesn’t fit. Is anyone aware of a low profile mounting solution for the inside of the rail? The stock MLok nut is too thick.

    Ive already ground down the screw so it doesn’t protrude.

    I had this problem on my 11.5" pistol upper. I didn't find a good solution. I did have enough rail to simply install the AFG a couple inches closer to the receiver. It's OK in that spot, but it's not exactly where I would like it. Ideally it would be out to about an inch from the end of the handguard.

    p86FD0a.jpg
     
    Last edited:

    Vigilant

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    I’m assuming the MCMR is all the way out to the muzzle device. I will have to look, but I think I have bought M-Lok nuts that were at least half thickness just so they could be used all the way out on carbines with 15” rails. The drawback is they are not as strong, as only 1 or 2 threads actually engage. Easy button would be to move the AFG back just a bit, but that’s probably not what you want to hear. Stay tuned, I will be back in Indy Sunday, and I will look to see where I bought them. Or, I’m totally misreading this, I’m Irish, and 3/4’s of the way to tomorrow, so...
     

    masterdekoy

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    Seedubs, It’s a superlative Arms adjustable with the set screws. I could probably take some material off the bottom but figured I would ask this before I broke out the dremel.

    Moving the AFG isn’t really doable as it’s an 8” rail. There’s not much real estate rear of where it’s mounted.

    Vigilant, that’s exactly what I’m asking about, thanks. It doesn’t have to be super strong, the AFG is pretty solid with one screw.
     

    d.kaufman

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    Hobart
    I have a key mod rail i was having the same issue with. I wanted to mount my afg in a certain location but gas block wouldn't allow it.
    What i did was remove the nut and screw from the rear of the afg and place the nut in the rail and hold it in place with a 90° angled pick, then slid the afg into position and reinstalled the screw. It was the fact of how loose it had to be to get it to slide into position that wouldnt allow it to go into position under the gas block, but resting in what would be the tightened position it fit under the gas block just fine. Maybe this will work for you
     

    MCgrease08

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    Earth
    I have a key mod rail i was having the same issue with. I wanted to mount my afg in a certain location but gas block wouldn't allow it.
    What i did was remove the nut and screw from the rear of the afg and place the nut in the rail and hold it in place with a 90° angled pick, then slid the afg into position and reinstalled the screw. It was the fact of how loose it had to be to get it to slide into position that wouldnt allow it to go into position under the gas block, but resting in what would be the tightened position it fit under the gas block just fine. Maybe this will work for you

    Interesting. I will try this.
     

    masterdekoy

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    56   0   0
    Feb 12, 2013
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    Columbus
    I have a key mod rail i was having the same issue with. I wanted to mount my afg in a certain location but gas block wouldn't allow it.
    What i did was remove the nut and screw from the rear of the afg and place the nut in the rail and hold it in place with a 90° angled pick, then slid the afg into position and reinstalled the screw. It was the fact of how loose it had to be to get it to slide into position that wouldnt allow it to go into position under the gas block, but resting in what would be the tightened position it fit under the gas block just fine. Maybe this will work for you

    Thanks for the suggestion. I actually tried this already. There isn’t enough clearance between the gas block and the rail to get a nut in place. Going to have to take the grinder to something.

    I don’t have any keymod handguards but wonder if they have lower profile hardware on the inside the handguard. Maybe this is why BCM was so resistant to M Lok?
     

    d.kaufman

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    Hobart
    Thanks for the suggestion. I actually tried this already. There isn’t enough clearance between the gas block and the rail to get a nut in place. Going to have to take the grinder to something.

    I don’t have any keymod handguards but wonder if they have lower profile hardware on the inside the handguard. Maybe this is why BCM was so resistant to M Lok?

    What about sliding the rail forward, installing your accessory and then resecuring the rail?
     
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    Sep 3, 2010
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    Kind of a PITA solution but if you're attached to the gas block swapping the rail out for a keymod would probably work. There are numerous keymod accessories that have less of a footprint inside the rail due to the shape of the key mod mount.

    Alternatively maybe consider a comparable off-brand product? I've used the keymod version of this Ebay AFG before and it's nice. It appears this option has the MLOK mounts further apart, possible avoiding hitting the gas block entirely.

    https://rover.ebay.com/rover/0/0/0?mpre=https://www.ebay.com/ulk/itm/253598792829
     
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