Make Your Own; A2 Sight Base

[98Z5V]

Well, Armalite discontinued their clamp-on A2 Front Sight Base; I don't know when they did it, but it was an excellent piece of kit. Ive used two of them in the past, and they really work well. Alas, they're gone forever now...

This is the old Armalite setup... you can still find old-stock, but even Optics Planet wants $75 for one.  I used to pull these things for $40 on sale (no sight assembly in there)...

So, I've got a project coming up, and I NEED an A2 FSB that I can use on a barrel.  The search for clamp-on versions will eventually lead you to Daniel Defense.  Wow!  What a NICE A2 FSB!!!

Another one that you'll probably find is the JP A2 FSB, that's got adjustable gas - again, Wow!  What a nice piece of hardware!

And... on both of those - Wow!  What a PRICE on those things!!!

So, into the parts boxes I go. I found an old Colt F-Marked FSB in there, complete.  Still had the front sight post,spring, detent in it.  Bayonet lug and front sling swivel, too.  So, out with the front sight assembly, off with the sling swivel, and it went to work with me.  I chopped off the bayonet lug and the sling swivel ears, and ran the bottom over the belt sander to smooth everything out.

There are 5 holes in this thing already - the bottom hole was there between the sling swivel ears, because that's the hole they use to drill the gas port in the FSB. The other 4 holes are 2 each side, where the tapered pins went through.

We're off to the races now - you'll need a #29 drill bit, an 8-32 tap, and (6 each) 8-32 set screws.

You WILL need an automatic center punch, as well.  You should have one of these in your toolbox, anyway, so you can "stake" your carbine endplates into their lockrings - one guy that was here called that "mangling" your parts.  I just call it "the right way to do it..."

Your choice - I had a bottom hole at the back, and also wanted one at the front - you mark it's proposed location with the center punch, drill it, and you're set.

You should pass the #29 drill bit through all 6 holes - you'll find that it barely touches the larger sides of the tapered holes, and barely touches the bottom hole, that was already there - that's okay.  You will need to drill up the smaller sides of the tapered holes, and that new front hole that you just made.  After drilling everything, tap them all with the 8-32 tap.

This is the front, where you'll need the new hole...

These 6 set screws will lock this thing onto your barrel like nobody's business - have no fear of it shifting or twisting...  unless you're trying to beat someone's a$s with your rifle... 

Edited July 1, 2018 by 98Z5V

[Robocop1051]

Fuckin genius!!! Six set screws, with a bit of red dabbed on the threads, will be solid AF! A half dozen dimples (although I doubt they’d be necessary) would make it even more solid. 

 

FWIW.. PRI has a clamp on version as well. I’ve used it successfully on several LW builds. 

[Robocop1051]

This is ? worthy!!!

[98Z5V]

16 minutes ago, Robocop1051 said:

Fuckin genius!!! Six set screws, with a bit of red dabbed on the threads, will be solid AF! A half dozen dimples (although I doubt they’d be necessary) would make it even more solid. 

 

FWIW.. PRI has a clamp on version as well. I’ve used it successfully on several LW builds. 

I've got two of those PRI crossbolt units - Mk12 Mod 0 and the 16" 300BLK with the PRI rail - love those things, but I wanted a fixed front sight base on this M4-gery...  

The PRI:

15 minutes ago, Robocop1051 said:

This is ? worthy!!!

Sweet!  

[Robocop1051]

There’s also the ARMS 41-BL Flip up A2

[Robocop1051]

Don’t give me wrong though. The PRI and the ARMS do not detract from the level of genius of your A2 modification. I love it. 

TBH, When I first started reading this thread, I half expected you to split the two bottom lugs with a linear cut, drill and tap them, and run your own crossbolt system

[98Z5V]

14 minutes ago, Robocop1051 said:

TBH, When I first started reading this thread, I half expected you to split the two bottom lugs with a linear cut, drill and tap them, and run your own crossbolt system

My initial thought was to do that, but there's not enough meat there to run a crossbolt through, unless you do cut into that barrel, and "channel" it for the crossbolts.   I didn't want to cut into the barrel, which is why I didn't just get a taper-pin reamer and go that route. 

Set screws!   Ding, ding, ding!  ...when the light finally went off in my brainpan...  I don't know if the barrel has any dimples on it yet - it get's here next week.  If it's not dimpled, those two bottoms will get a dimple for this sight's bottom set screws, and the sides will just get snugged up.  They'll all get a dab of red loc-tite, or Vibra-Tite, or just some Rock-Sett.  Any way you slice it, this thing isn't gonna budge.  

Edited July 1, 2018 by 98Z5V

[Robocop1051]

Excellent plan

[Mjolnir]

Well played 98Z5V! 

[blue109]

Nice mod!

I havnt seen much feedback on the DEZ fsb but it might be an option if you want a bayo lug

https://shop.deztacticalarms.com/A2-Fixed-Front-Sight-Clamp-on-750-w-Bayonet-Lug-DEZ-1035-GB.htm

 

On the other hand, a bayonet is a bad idea if the fsb isnt pinned. 

 

I really want one of those ARMS sights for my 14.5 with the CASV

Edited July 2, 2018 by blue109

[308kiwi]

Great idea, and a whole sh*tload easier to do than drilling, reaming and pinning.

[survivalshop]

$hit 98 , DEZ ripped off your Idea ! ?      Ya a Bayo lug is a bad idea on that type of attachment .

[jtallen83]

11 minutes ago, survivalshop said:

    Ya a Bayo lug is a bad idea on that type of attachment .

Bad idea to use it, nice to have just because it scares snowflakes. 

[98Z5V]

1 hour ago, survivalshop said:

$hit 98 , DEZ ripped off your Idea ! ?      Ya a Bayo lug is a bad idea on that type of attachment .

I saw that - bastards...  

[98Z5V]

Zapped it with some Cerakote this morning, and tossed the front sight post back in it. Goes on a barrel Friday.

[392heminut]

I like the serrations on that Daniel Defense FSB! Never thought of doing something like that but then again, I don't mess with FSB's like that much.

@98Z5V, I can do that serration stuff if anyone wants it but you'll have to put a finish on it afterwards. Just mail the FSB to me and I'll knock it out and send it back the next day.

[98Z5V]

59 minutes ago, 392heminut said:

I like the serrations on that Daniel Defense FSB! Never thought of doing something like that but then again, I don't mess with FSB's like that much.

@98Z5V, I can do that serration stuff if anyone wants it but you'll have to put a finish on it afterwards. Just mail the FSB to me and I'll knock it out and send it back the next day.

I'll Cerakote the hell out of it, too, and make it FLAT FLAT, so there's not a chance it will ever glare on you...   The DD serrations are brilliant.  You see it on front sights on bolt guns all the time, and some pistols - but DD is the only one to pick up on that and offer it on an AR front sight base.  That kinda shiit should be standard issue, it's so damn smart...  

 

Edited July 24, 2018 by 98Z5V

[JSullivan]

Has anybody ever thought of finding the drill & tap size for threads closest above the small side of the taper pin holes even if having to up drill slightly and also creating a flat-bottom countersunk hole for a hex socket cap screw of that size tap on the large end size of the taper pin holes and then splitting the rings on the bottom side (perhaps with a hacksaw or similar) to create a clamp on version.  Obviously depending on the size of the ole location a round file will likely need to be used to create cross-channels in the bottom side of the barrel for the space where the threads of the caps screws would interfere as long as the cap screws do not protrude too close to the barrel bore and compromise integrity.

[StarWolf]

On 7/1/2018 at 2:00 PM, 98Z5V said:

My initial thought was to do that, but there's not enough meat there to run a crossbolt through, unless you do cut into that barrel, and "channel" it for the crossbolts.   I didn't want to cut into the barrel, which is why I didn't just get a taper-pin reamer and go that route. 

Set screws!   Ding, ding, ding!  ...when the light finally went off in my brainpan...  I don't know if the barrel has any dimples on it yet - it get's here next week.  If it's not dimpled, those two bottoms will get a dimple for this sight's bottom set screws, and the sides will just get snugged up.  They'll all get a dab of red loc-tite, or Vibra-Tite, or just some Rock-Sett.  Any way you slice it, this thing isn't gonna budge.  

Glenn Zediker goes through a very similar evolution to produce a set screw A-frame front sight in his 2010 book The Competitive AR-15 Builder's Guide. I think he set it up for two set screws however. Apparently he passed away during the late unpleasantness.

The first couple barrels I dimpled were cake.
The last couple barrels I attempted to dimple were a cast iron pain in the posterior.
I'm not certain if a cutting  punch to break through the Nitride would have helped out or not.

Edited April 26, 2023 by StarWolf

[Disguntled]

To really make the FSB stay put, I file 2 small flats on the bottom of the barrel for the set screws make a solid contact.  You could also dimple the barrel as well like they do for the low profile gas blocks.

[98Z5V]

On 9/11/2024 at 12:24 AM, Disguntled said:

To really make the FSB stay put, I file 2 small flats on the bottom of the barrel for the set screws make a solid contact.  You could also dimple the barrel as well like they do for the low profile gas blocks.

Provide pics of that, the finished work, and we'll definitely incorporate that into the process.  That would be badass, with pics of the finished product.