Machinist / 'smith recommendation for pinning gas block - Mk12 Mod0 flip up sight

[tresmonos]

I couldn't find my unique situation via search:

I'm building a Mk12 mod0 clone and have decided to forego the set screw PRI flip up gas block in favor of pinning it in place.
Questions:
1) Do you know of any gun smiths or machinists that will pin the PRI flip up sights in place?
2) am I crazy to assume the set screw style PRI flip up sight would work (major diameter of the set screw = diameter of through hole)?

I pulled the trigger on the diameter cross bolt sight because I was going to be lazy so I know I'll have to return this (not a problem) as it wouldn't work for pinning unless i drilled out for a larger diameter pin.

Makes me wish I had the gumption to get a good drill press and do this myself. Fixturing would be tricky, but I think I could do it.

[scottryan]

tag for later reading.

[tresmonos]

Rather than mess with pinning through set screw through holes, I'll pin it in the manner depicted in the attached image. Any recommendations for a machinist? I hear ADCO does it. Any others?

Also: If I decide to do this myself, is there a method to pinning / reaming hole to size? Is there a recommended pin size? Is there a preferred drilling location or do I just square up the hole to intersect the plane of the pinning surface?

[tresmonos]

I feel almost assinine answering my own questions, but just in case someone else needs this info and doesn't feel like searching on TOS:
For my base point, Colt's taper pin size are: 2/0 "(.125"/.140"). and come in .375" and .5" lengths.
Drill bit I'll use: .12" (#31), since the small end of the 2/0 taper pin is .125". Most likely I will get a .375" or .5" length and file it down if it's too long. I'll buy a #0 pin in case I open up the hole too much.

For the jig I'll figure something out. I've assembled AK's with home made jigs, so this shouldn't be difficult. I may do some rough measurements with my calipers on the PRI sight to see if I could pick up a jig off brownells to keep the FSB level when drilling. Or I'll rely on it's bolt 'clamp' to secure it to the barrel and fixture the upper receiver in a vice block and drill post assembly. I may come back to this thread with some pictures once I get back to the states and assemble this pile of parts. But all of that is already on TOS.

[scottryan]

Rather than mess with pinning through set screw through holes, I'll pin it in the manner depicted in the attached image. Any recommendations for a machinist? I hear ADCO does it. Any others?

Also: If I decide to do this myself, is there a method to pinning / reaming hole to size? Is there a recommended pin size? Is there a preferred drilling location or do I just square up the hole to intersect the plane of the pinning surface?

You cannot pin the clamp on front sight base. Am I understanding you correctly?

[markm]

Rather than mess with pinning through set screw through holes, I'll pin it in the manner depicted in the attached image.

That's a completely jacked up way to pin. It's correct to pin on the BOTTOM of the FSB so that the pin tension pulls the FSB down onto the gas port creating a better gas seal.

Granted that's a roll pin, and not the same as a taper pin... but I still don't like it.

[tresmonos]

That's a completely jacked up way to pin. It's correct to pin on the BOTTOM of the FSB so that the pin tension pulls the FSB down onto the gas port creating a better gas seal.

Granted that's a roll pin, and not the same as a taper pin... but I still don't like it.

Right on. This is exactly why I posted the question.

scottryan:
There are two PRI flip up sights: set screw mount and bolt clamp style. I was going to keep my clamp style, secure the block via the bolts, then pin at the top to keep it in place. But I want to see if I can use the set screw style and pin that sight/block through the set screw threaded through holes.

I just called PRI and they're going to reference their set-screw style drawings for the locaiton of the threaded holes for their 10/32 screws. So it's a .19" major diameter. I'll need a larger tapered pin.

[tresmonos]

PRI returned my phone call (I think it was Tony and Shaun who I talked to), they pulled up the print of the set screw style mount. .35" from center line of bore to center line of threaded through hole of set screw style mount. That wouldn't leave much barrel if I used a .1875-.19" tapered pin to hold it in place. Both of them didn't recommmend that method.

That picture I found is actually a PRI assembled bolt clamp style front sight. They indicated that is their method for securing the sight for a number of contractors (their words, not mine).
They use a .15625 (5/32)" diameter round pin, .625 (5/8)" in length. Shaun said I could use a .125" if I wanted. I expressed markm's concern about how the sight is anchored to the gas port. He explained that the clamp is the force securing the block. He actually clamps the block on, sights in the rifle then pins it. He recommended that I do the same. The pin is only there to prevent the block from being knocked loose.

So to keep the spirit of the replica build, I'm going to proceed with the clamp style I currently have, and will pin it in the same manner as illustrated in the pic (not with a tapered pin, thank you markm), as I really don't see another viable locaiton to pin either style of sight.

[scottryan]

So to keep the spirit of the replica build, I'm going to proceed with the clamp style I currently have, and will pin it in the same manner as illustrated in the pic.

I don't understand why you don't use the set screw version since this is authentic for a read mod 0 spr.

[tresmonos]

I don't understand why you don't use the set screw version since this is authentic for a read mod 0 spr.

I'll swap the clamp style with the set screw. Pin in same location as pic.