I have a 12 gauge semi (no rib) that has a blade front sight, but no factory rear sight. It comes from the factory with two 3/8" rimfire dovetail cutouts in the receiver. Anyone know of an aftermarket 3/8" dovetail mounted adjustable rear sight? Preferably one that doesn't cost an arm and a leg?

Try here, thy have lots of parts.

Try here, thy have lots of parts.
https://www.midwestgunworks.com/gun-parts.html

Thanks Old Timer. I'll check it out. (If subsequent posters have suggestions, please feel free to post them)

In case anyone stumbles on this in the future, this is the best option I found:

11mm-Dovetail-to-20mm-Picatinny-Weaver-Rail-Mount-Adapter-10-Slots-Aluminum



https://www.ebay.com/itm/11mm-Doveta...m/274319468842

When I first saw this post I said to myself " I am looking for the same thing". As it turns out, I am looking for a scope mount base IPic or weaver) that fits into a 3/8" dovetail cut perpendicular to the barrel axis. In other words, to replace the existing factory dovetail for the iron sights. Don't wish to high jack the thread, so if any one knows of such a thing, please PM me.

I got that rail and the dimensions are wrong. I'm going to have to get out the ole' dremel to make it work. Sucks, but ultimately it is salvageable, I think. I'll update and post pix when all is said and done.

I was picturing a perpendicular dovetail SLOT, not a rimfire type dovetail rail.

For 3/8” dovetail rails, I have used several of the inexpensive UTG dovetail to picatinny adapters under red dots or even scope rings.

For an iron sight option, a Marlin style rear sight from Tech Sights may work. They assuredly will fit a 3/8” dovetail, but may not be the correct height for this particular front sight blade. Old Marlin 99 rear sights are quite low, and mount on 3/8” dovetails as well, although they’re quite challenging to find, and oft expensive when found.

I tried one of those first, but the sight I was using, a Sig Romeo 5, went flying under the recoil of a 1600fps 1oz deer slug after about 100rds of various 12ga. That said, I only had it mounted on one dovetail, if i used both to mount a more proper pic rail on them and then mounted the Romeo5 to that, it might work.

You can try Numrich arms or Brownells or Dixie Gun Works for the sight that was for your model shotgun.