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Thread: Gas Block Clearance

  1. #21
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    Re: Gas Block Clearance

    I used a machinist ruler to confirm that the rail is aligned properly.

    How can I check the barrel?

  2. #22
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    Re: Gas Block Clearance

    Quote Originally Posted by mtdawg169 View Post
    Dammit, I was getting ready to order a CMR, but I keep seeing fitment issues. Does anyone have Vltor & BCM gas blocks sitting around that can measure them for overall height? I'd order a Centurion gas block, but those are no where to be found.
    I should have done that before grinding the block.
    Last edited by netchemica; 06-10-13 at 17:25.

  3. #23
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    Has anyone tried a LaRue low pro GB with one of these rails?

  4. #24
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    My take on spacing

    Here's my opinion... strictly an opinion based on why we free-float barrel. Keep in mind that I'm talking only about any type of handguard which only connects at the barrel nut area.

    We free float AR barrels because we don't want to put extra pressure on the barrel as we grip the front of the rail system. If the guard is installed correctly, for example DD Lite & VTAC... the rail should be rock solid with little to no flex. That being said, if there is just a tiny bit of daylight between the block and inside of the rail... then the barrel is still free floating. Even if I was gripping the rail in such a way that would put extra pressure on the frontend... the rail should not be able to flex enough to touch the block. And if we are worry about barrel flexing, that doesn't happen until the round has left the barrel.. so it shouldn't affect accuracy.

    My opinion, based on the info I gather above… is that as long as there’s day-light, I think you’re good. Best way to tell, take it out to the 100yd line and do some accuracy testing on sandbag. In all honest opinion… I’ve shot a standard 20” A2 out to 200 yards on sandbags using irons and the standard A2 handguard… it was just as accurate as my free-floated AR.


    dc

  5. #25
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    Deleted
    Last edited by davidjinks; 06-12-13 at 21:40.

  6. #26
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    Just another thought, but the Geissele SGB has a very low profile to it. I just installed the Nitride SGB and I was very impressed with the profile of it, I had the FSP shaved but it was kinda choppy and I was having the same clearance issue and it basically sat against the MK2 rail and I kept thinking is this eventually going to cause an issue, once I got the MK4 rails I had a bit more clearance but still wasn't comfortable with it, I decided that I wanted to go another route then the MK4 so while waiting for them I installed the SGB, after I find the rails I want to keep I do have the option to pin the SGB, the coil pin hole is already present which is a nice feature and comes standard in Geissele's SGB


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  7. #27
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    dremel and grinding wheel is all you need. leave the top and take the bottom down some more. and round off those corners

  8. #28
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    A couple passes with an angle grinder was all I needed to gap the Rainier block. Touched up with a black sharpie, and all is good in my world again.

    Kind of nerve racking for a couple seconds as the grinder spun up though...

  9. #29
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    Gas Block Clearance

    Quote Originally Posted by ROK View Post
    Touched up with a black sharpie, and all is good in my world again.
    Alumablack also works really well for touch up.
    Last edited by munch520; 06-14-13 at 21:23.

  10. #30
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    Quote Originally Posted by netchemica View Post
    Is there a spec I can go by? Will this tiny gap affect my accuracy at all?
    Quote Originally Posted by netchemica View Post
    Is there a "rule of thumb" / clearance specification that I can follow?
    Quote Originally Posted by CGS View Post
    A dollar bill is the rule of thumb used for bolt actions when free floating around the stock.
    I had always heard that if you could slide a business card between the barrel and stock, then that was enough clearance... That was for a normal stock, where any tension from the sling would pull the stock down, away from the barrel. On an AR, where slinging up would pull the handguard down onto the gas block, I would want to maintain that much clearance under tension.

    And yes, I think it matters... what's the point of installing a free float handguard if it's going to contact the barrel at the gas block?

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