Chopping the FSB vs buying a low pro gas block

Discussion in 'AR-15 Discussion' started by indyfan, Jul 8, 2011.

  1. indyfan

    indyfan New Member

    I wanna put a flip up front sight on my BCM AR-15 which currently has a front sight base. I was told by a friend that it's better to chop off the top of the fsb as oppose to buying a low profile gas block.

    I was originally going to buy a YHM flip up front sight base, but was also advised against it by my go-to AR buddy.

    Any thoughts on this? or what I should do?

  2. Sniper03

    Sniper03 Supporting Member Supporter


    Have you got a pic of your rifle. I am assuming you have the standard front sight assembly on it? And am also assuming that you want a standard style front sight gas block flip up front sight Post? Just so I understand you correctly look at the Rock River Website and check out the RRA Flip Front Sight Gas Block Assembly or the A.R.M.S 41B/L Silhouette Folding Front Sight. Nothing wrong with Yankee Hill or others either. If you cut off the front A-2 Front Sight (A Frame) on yours you will need to make it look decent which requires a little work nothing overwhelming! So then, are you going to get a Free Float Quad Rail and mount the new sight on it? Just want to be sure we know where you are going with your project before we give any direct advise.:)


  3. Car54

    Car54 New Member

    Removing BCM FSB Taper Pins
    From speaking with customers, it seems BCM FSB taper pins are harder to remove than some others. When we do it here, we can knock the pins free in under 60 seconds.
    Here are some basic pointers on the way we remove them.

    1) It takes Two. You will need a buddy to hold the upper group stable as you pound out the pins. You will not be able to get a good concentrated force on the pins if the upper is wobbling around (even a little bit).

    2) Action Jackson. You will need a couple of action blocks (see Brownells for a good selection). These will be great platforms to stabilize the barrel. Also get the Brownells FSB block. You may have to mod the shape of the FSB block if using a free float.

    3) Installed from starboard side. Milspec FSB are drill and the reamed for taper pins. The reamer runs from the right to the left (pointing the muzzle at the bad guy). So BCM pins need to be removed from left to right. Cannot be done the opposite way.

    4) Secure that carbine. Using action blocks and the buddy system secure the upper group so the left side is facing up.

    5) Get a fat one. We do not use those small radius head punches to break the pins free. We use a much fatter punch (5/16”). It’s a meaty sucker. Lots to hang on to, and enables you to put some force on the hammer. Using a 5/16” punch and a 12oz hammer, give her a smack. Anywhere between 1 and 6 smacks, and the pin moves. All you want to do is to get it to move to about flush.

    6) Grab a skinny one. Now get the tiny little 1/8” punch to push the pins out of the FSB. They are already broken free, this just drives the fully out. Tap, tap, tap.

    7) Celebrate. You are done.