AR-15 Front Sight Base Installation Question

[coloradokevin]

So, I've built an AR-15 in the past, originally because I wanted a rifle that was built to my exact specifications, and couldn't find what I was looking for on the market. I used a pinned low-profile gas block on that build, and the barrel and block had already been drilled for pin installation by the barrel manufacturer.

I'm now eyeing another build, and I've been thinking of doing an f-marked A2 style FSB on a mid-length gas system chrome lined ultralight/pencil barrel. Problem with this build idea is that it seems like drilling the FSB/barrel for taper pin installation isn't an easy task to do at home, and I haven't seen this barrel setup sold with the FSB pre-drilled.

Have any of you completed this task with home shop tools? I'm not really big on the idea of a screw-on, clamp-on style FSB, and would prefer to pin this build. But, I'm not sure how to go about making this happen in a home shop (certainly don't want a crooked sight post!).

If all else fails I may default to another build with a low-profile block… But, I was kinda eyeing a bayonet lug for this particular AR-15, and that simply isn't available in the low-profile blocks.

 

[444]

I went through the same dilemma as you are.
I am sure it can be done but I decided it was beyond me because I wasn't sure I could get it exactly straight.

I sent my barrel to Adco and had them do it.

https://www.adcofirearms.com/shopservices

 

[badkarmamib]

Without a GOOD drill press and bits, I wouldn't even consider attempting drilling the pin holes, I would send it to someone who does it for a living. Also, you definitely don't want to use a bayonet with a clamp-on base, it wouldn't hold up to that kind of pressure.

 

[adcoch1]

I did one a while ago for a friend's upper(xm177 clone) and even with a drill press it was a hassle. Check with the company listed above, or any local build shop and see what they charge to do it. I have a lot of machine tools and have built a ton of ar15s but its still tedious without a proper jig for it.

Sent from my LGLS740 using Tapatalk

 

[coloradokevin]

Yeah, that's what I was afraid of… seems like this isn't an easy task to do at home, nor is it a cheap task to farm out to someone else.

It's tough when you know what you're picturing in a rifle, figure it should be cheap to put together, then find that it isn't going to turn out that way (hmmm… that sounds like every gun build I've ever been a part of, LOL).

I did find this product online, but I'm not sure how easy it is to use in a home shop:

http://brdengineering.com/products/front-sight-base-fsb-jig

I don't currently have a drill press, but have been thinking about getting one. My concern is that I may need a milling machine to do this kind of work accurately. Hmmm.

 

[atblis]

I just did exactly what you're asking using a drill press. It's not an easy task, but you don't have to be an expert machinist to do it either.

First, you don't need that jig. Do this instead.
1) Attach the barrel to the upper
2) Sight in the rifle using a reddot like an Aimpoint attached as far forward on the reciever as you can go leaving room to put a rear sight on. I have a cut down carry handle which is basically the LMT rear sight. You can shoot the rifle with no gas block. If it makes you feel better, use a clamp no/set screw block temporarily.
3) After sighting in the reddot, using a windage centered rear sight, put the front sight on and adjust so it cowitnesses with the reddot. Use green bearing retainer loctite on the front sight(few different flavors, but 609 should work). I've done this a few times, and there is no better way to get the front sight perfectly lined up. With the loctite, the sight will not move while you're drilling and pinning. I shot a gun for several months in matches using a sling on the FSB using only loctite. While you're at it, you can also adjust the front sight post for elevation using the reddot.
4) Drill, ream, and pin away!



I watched this guy's video it was the most helpful. I recommend using the spacer he makes as the handguard retainer got in the way of my drill press when trying to drill.
https://www.youtube.com/watch?v=O6BlViDghKY

It's real easy to over ream. Go slow and check often. Nothing worse than putting in a lot of effort, and then screwing up on the last step!

I simply squared up my drill press using a dial indicator. Used V blocks on the barrel. A Drill bit in the sling swivel compared to a chucked bit to orient the rotation of the barrel. Eye balled the locations of the holes. Hand reamed. Done.
https://www.youtube.com/watch?v=jdQ7Uo7oG7I
https://www.youtube.com/watch?v=_yWdZAC1w2I

Really the hardest part was figuring out a way to line up and then secure the barrel on the drill press.

There's nothing special about the reamer. I bought it either off Amazon or Ebay for less than $10.

 

[444]

So when you got done, how close was it ? In other words, after you got done, did you have to adjust the rear sight very much to zero it ?

It sounds like you did a great job and I like the thought process. But, that is beyond me. I would screw it up somehow.

I had a buddy that built a semi-auto HK91 from a parts kit. He had basically nothing but common hand tools but he is the kind of guy like you that can work his way though something like this and improvise. He had some kind of set up in his garage with plumb bobs and levels and what-not. I thought the whole thing was ridiculous. When he got done, we took the rifle out to test fire it and the sights were dead nuts, right on the money and required absolutely no adjustment. It was very impressive to me. He didn't really think much of it.

 

[mjsdwash]

its not too hard, the easiest way is to tap out the hole for the gas port under the sling swivel and put in a set screw to hold it. Ive seen it done by putting vice grips on one part very tight, and drilling and pinning the other side with them in place too. to get alignment, I wrap a string around the carry handle, and the front site ears, and get the gap between the front of the carry handle and string the same on both sides. without an a1/2 upper it would be more difficult. The last time i did it, i used a hand drill, and carbide bits for 1/8 dowel pins. Its not the easiest thing, but i cant see paying$150 for someone to do it for me. whatever you do, do not drill using those gold colored drill bits, or any other "better" type, they are junk for steel. Start the drill by hammering with a punch to keep the bit from walking, and if necessary cut the bit so that its short enough to not flex when you start, and progress to longer bits when you bottom out.

 

[FL-NC]

You are really better off finding a barrel that you like with the sight already installed. Check PSA, Brownells, Model 1, and DPMS.

 

[adcoch1]

You are really better off finding a barrel that you like with the sight already installed. Check PSA, Brownells, Model 1, and DPMS.

This is ABSOLUTELY the easiest and quickest way to go. If you want to do it yourself go for it, but just about every idea under the sun is available at a discount nowadays...

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[ApacheCoTodd]

I made these from G.I. front sights and higher quality front sight tools.

Turn a dead center point for indexing after confirming concentricity of the permanently attached front sight post.

Confirm level of barrel assmbly in "V" blocks.

Confirm radial indexing using the pin on the barrel extension as your radial reference.

Set and fix your barrel assembly in "V" blocks.

Reconfirm level and radial indexing.

Confirm sight base radial indexing with the tool and set.

Be sure to confirm an alignment of the gas port in the barrel with the sight base and note whether a handguard ferrule is expected in any forward offset.

I like #0 x 7/8 taper pins.

Drill to established guide size and ream with established guide reamer.

A simple, appropriately sized, nail set punch is all you need to keep from mushrooming the ends of the taper pins.



Todd.

 

[Zach S]

I converted my 9mm and .45 AR15s to dissipators. I took the cheap route by doing it myself, and the easy route by using set screws...

Based on that experience, I would by a barrel that fit my needs, or have Adco pin the FSB for me.

 

[atblis]

So when you got done, how close was it ? In other words, after you got done, did you have to adjust the rear sight very much to zero it ?

3 or 4 clicks.