Canted Front Sight Gas Block

Mumbles Marble Mouth

Mumbles Marble Mouth

CGN Ultra frequent flyer
Rating - 100%
81   0   0
Location
Lower Mainland
I have a 20" pencil barrel I installed into my S&W M&P Sport II and when I took it too the range to sight it in, I had to crank the carry handle rear sight all the way to the right to get it zeroed at 25 meters. It's zeroed out to 100 no problem but it bothers me. Its hard to tell but I can see the front sight gas block is ever so slightly canted off to the right. I was going to pull everything apart and inspect the barrel index but then thought maybe I could try taping the gas block pins ever so slightly out and then bash the front sight with a rubber mallet. What do you guys think? Good idea? Bad idea? It works with scope bases when your scope doesn't have enough adjustment so I figured it may work with a front sight gas block. Its already zeroed and works would just like to move the rear sight over so I got some more adjustment rather than being right on the edge of no adjustment.
 
You are SOL on this one, drilling on top of the existing hole you are just making the hole bigger, you won't be able to secure your FSB with the taper pins anymore.
 
Unfortunately that won't work, the taper pins index the barrel, so once you properly orient the front sight and put the taper pins back in, it'll push the front sight off axis again. The taper pin holes are drilled through the sight base and barrel at the same time, so it's sorta a "one time" thing...

About the only way I could think of "fixing it" would be to machine through holes for roll pins instead of taper pins (not the best idea) or get a clamp on front sight base. Armalite used to make an A2 front sight base that clamps on. You could also try shimming the carry handle sight (assuming it's removable) to push it farther to the right side of the gun?
 
You could get a clamp on fsb a2 sight as a direct replacement. It should cover the taper hole once the old fsb is removed. Then you can properly align the sight. I did that one of my rifles, never had any issues. Wolverine supplies should have some in stock, or CTS supplies.
 
Last edited:
Well it worked. Pins are in all the way and I gained an extra 17 clicks according to the boresighter. Won’t know for sure until I shoot it and I marked the post to the barrel to see if it shifted. It did just a tiny bit but it was enough to get 15 extra clicks. Still not centred but having 15 extra clicks is a hell of a lot better than 0. I might think of another way to get a bit more as 45 clicks is center.
 
sgnu said:
You could get a clamp on fsb a2 sight as a direct replacement. It should cover the taper hole once the old fsb is removed. Then you can properly align the sight. I did that one of my rifles, never had any issues. Wolverine supplies should have some in stock, or CTS supplies.
Click to expand...

I might have to give that a try. Just looked them up and it looks pretty good. Some of them are really nice and still have the A2 profile but can fold down. This rifle is a donor gun for an ATRS receiver set so I have time to figure out what I’m going to do. My gas block dimension is also .625 so don’t know if I can find an appropriate clamp on gas block.
 
I found my solution. I found a post from a guy in the US who modifies the gas block to a 6 set screw gas block. Two from the bottom and two on each side of the block. Looks pretty simple.


Stevo said:
Cut the FSB down to retain the pinned gas block, and put a free float over the whole thing.
Click to expand...

I understand what you're getting at but I only like M16 20" barrel AR's with fixed front sight and carry handle. The easy solution is just to convert it to free float and use a scope or flip up sights.
 
Mumbles Marble Mouth said:
Well it worked. Pins are in all the way and I gained an extra 17 clicks according to the boresighter. Won’t know for sure until I shoot it and I marked the post to the barrel to see if it shifted. It did just a tiny bit but it was enough to get 15 extra clicks. Still not centred but having 15 extra clicks is a hell of a lot better than 0. I might think of another way to get a bit more as 45 clicks is center.
Click to expand...

Congrats on getting it sorted. I’m almost certain that US armorers used to use a similar method way back but I don’t believe that it’s in the latest repair manual.
 
The USAMU used to not pin them with the taper pins, and instead glued them on and ran set screws through them from the bottom of the FSB. Not sure if they still do that, but it worked for them, so something worth a try. Keep in mind, they didn't have the hand guards attached to the FSB in any way either.
 
You must log in or register to reply here.
Back
Top Bottom