drill and tap older Mossberg 500?

You will have to drill through the receiver. As a general rule you want to have at minimum the screw diameter in thickness of the receiver metal. I have an '80s 500 too and it came d&t'd from the factory. You should have enough thickness for your rail. If its boarder line then it would be best to drill a third hole in the rail so you can get more thread contact.

Just checked to be sure , if you would rather not drill, Brownells sells a saddle mount for the 500. Easy install.

New BBL;

jim-analog said:

Greetings,

I'm like to install one of the small holo sights on my late '80s model 500, which would require a short pic-rail section. The only "sights" it currently has are a small bead at the muzzle end and a rib going longitudinally along the receiver top. Reading about the newer 500 series versions, seems they are factory drilled. Any tips for locating the holes (figure I'd use the actual rail section as a marking template) but not sure about the best area to drill into, depth of drill, etc.? The receiver seems to be pretty thin and I'm not sure how much thread I can get. Thanks in advance!

Regards, Jim

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I have found through my experience that it is cheaper in the long run to buy a new barrel with a cantilever scope mount. I suppose the "holo sights" mount like a scope on the rail. I have mounted scopes to the receiver of a 500 and found it difficult to keep the scope sighted in. Mounted on the bbl the scope stays zeroed in. Not that old 500's are of much value but you wouldn't depleat any value with a new bbl.

Greetings,

Thanks everyone!

Regards, Jim

I was able to drill and tap my Mossberg 500 for Picatinny rail

This is how I did it.
UTG MB500T rail with screws from Amazon.
A9 aluminum tapping fluid, Amazon
Remove the barrel and receiver from the gun. Used the rail to layout the holes. The screws are M4 so I used a #28 drill bit (~3.5mm).
Using plenty of A9 I drilled the holes and removed any burring on the inside emery cloth. The cap screws have a 36 tpi (.7 metric) thread pitch so use the proper tap(4M/.7). Go slowly, use A9, and back the tap up and out and clean it as you go. I run the tap the through a second time and then run a Qtip through to clean all of the oil and debris. Use copious blue loctite and don't over tighten the screws. The rail snugs down nicely with the 4 cap screws. I'll post a follow up after more rounds but after 50 she's still tight.

I had a Mesa rail put on mine and mounted a red dot. When the Zombie's attack the ones wearing "O" shirts will take a precision shot to hit the tiny brain.

I think the side mount is a better option. But that is just my opinion. http://www.brownells.com/optics-mou...gun-bases/shotgun-saddle-mounts-prod1779.aspx

philip26p said:

I think the side mount is a better option. But that is just my opinion. http://www.brownells.com/optics-mou...gun-bases/shotgun-saddle-mounts-prod1779.aspx

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not to jump on your thoughts, but, to me a side plate is a pain to pull the trigger group out in the field if needed. I have used them and went to a pic rail also. A local smith would probably charge around $50.00 to do it if you are not comfortable on your own.