Installing a front sight on a plain barrel shotgun


October 29, 2005, 11:40 PM
Years ago I had a smith cut my home defense Mossberg for choke tubes, which left only a few threads to retain the original bead sight. It didn't last long. I plan to drill and tap a new hole behind the choke tube and install a simple replacement sight. Put the hole in the right place, trim the shank of the new sight so it doesn't protrude into the bore, Loctite, etc...

I'm wondering how a replacement sight, such as the Marble Arms ( or Meprolight (, is timed so it aligns correctly with the shooter's perspective?

The gun has a light, so I really don't even need tritium. I like the easy installation of the MMC front sight (, but I don't think I want such a busy sight picture. It looks pretty high, too, but POA/POI might not be a big deal for across-the-room application...?

Any advice would be appreciated.

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November 4, 2005, 06:51 PM
Bump to add another specific question:

What thread size for a new sight? It's going to be a new hole, so options are wide open. I'm leaning towards the Marble Arms sight, with the following thread options:



November 4, 2005, 07:32 PM
I would start out with the smallest hole. If you mess it up or it needs re-tapped in the future all you have to do is re-drill and tap the next bigger hole

November 5, 2005, 01:14 AM
" options are wide open..." not really. You'll have to drill and tap for the thread on the sight. 6-48, I think. The trick is to get the hole absolutely dead top center on the barrel. I was always able to eye-ball it, but I had done that sort of thing many times before. The best way is to measure the diameter of the barrel where you want to drill(No hand drills. Drill press and a Vee block only), half that and with the barrel dead square to a flat surface, make a wee scribe mark and drill the proper size hole(a # 31 drill) for a 6-48 screw. Tap, Lock-tite and screw the sight in.
You'll have to re-pattern anyway.

November 5, 2005, 04:20 AM
What I meant was I don't have to select a sight with threads that match the existing hole, because I won't be using that hole. I can make the new hole fit whatever sight I choose. Drill press and blocks for sure.

6-48 and a #31 drill. Thanks!

How about timing the sight? The Marble Arms sight, for example:

When it's tightened down, the tritium end has to face toward the shooter, and I don't imagine that's something I can control by starting the tap in just the right orientation. I'm guessing I'll have to shim the sight by trial and error until it lines up correctly, unless there's another method.

Thanks for the suggestions, guys.

November 5, 2005, 04:40 PM
You need a shotgun bead facing cutter from Brownells. It cuts off the bottom face of the bead/sight. Check out the following link:

November 6, 2005, 11:01 AM
Well, there's a fly in the ointment. Thanks for the link.

November 7, 2005, 03:58 PM
An alternative that might look better would be a solder-on sight base:


November 7, 2005, 04:31 PM
Looks aren't a big priority, the gun is in "hard use" condition. ;) A base and sight combination is a good idea, though.

I need to pattern some more loads, but it looks like the gun tends to shoot high. If so, I'd like to correct the POA/POI difference. And for consistency with my other guns, I'm looking at a squared rifle sight instead of a round bead. Hmmm...
November 13, 2005, 01:18 AM
I have the Trijicon on my Mossberg. I filed the base until the glowing portion of the site was facing me. I squared it in a v-block. (Not necessary; mainly for looks.)

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