I have bead sights on both my 870s and want to replace them with tritium (specifically) the Marble tritium unit in my Brownell's catalog - looks like a best option for me as I shoot well and am familiar with the bead sight.  

Are the stock units 6x48?  Any tips on removal and installation? Tools ?
These are an 870 Police and 870 Express both with bead sights.

The bead and base on the barrels are not screwed on, they're brazed on and are a MAJOR PITA operation to get off.  
You have the option of heating the barrel to a red heat to melt the high-temp brazing, or cutting the bead and base off.

If you heat, you run a risk of damaging the barrel, and it will require re-polishing the inside of the barrel, and refinishing the outside.

Cutting the bases will leave a bare spot, which may be covered by the new sight, or it too will require a refinish job.

After you get the beads off, you have to braze the new sights on, or drill and tap for screws.
Drilling for the front requires trimming the screws inside the barrel, since they will be too long, and this also requires polishing the bore.

Here's some options.
1. Just buy new barrels with luminous sights already installed.  
I assume Remington sells Police barrels already with the sights, and the Police will fit the Express.

2. Buy the Wilson type front sight that is epoxied OVER the front bead's base.  The Wilson company installs these with epoxy AND a cross pin to hold it tight.
The problem here is in mixing different manufacturer's sights, which may not be compatible on height.

My advice:  Cut the bead sight off the barrel.  This is less risky and doesn't require a refinish.
I use a jeweler's "wire saw" or a GOOD hacksaw to cut as much off as I can WITHOUT scarring the barrel.

Then I use a bench grinder to take it close, again being careful not to scar the barrel, then finish with hand files.
This works well, and you'll have to do the filing anyway to remove the brazing even if you use heat.

Thanks - ugh!

The product I want to install isn't a ramp sight or anything more elaborate than what appears to be a bead replacement.  How is the present bead installed on the front sight base?  I don't need to remove the base, just the bead itself.  (Thus my query about thread sizes).

Here's the thing:



Is the bead itself brazed into the base?

I don't have experience with the "bead on the block" remington barrels. Some of these setups, the bead is pressed (no threads)into the block and the block is applied to the barrel. You shouldn't have to remove the block from the barrel though..........
I would wait to see if others replied before doing anything. Call Remington and ask a tech person maybe? I dont want to tell you "Yea it is 6-48- go for it"; just to find out they went to pressed in beads!

"AS FAR AS I KNOW" (note the qualifier), the Police gun's bead is threaded in the base.
The Express is pressed in and typically breaks off if you try to remove it.

In the Police gun's case you carefully unscrew the bead.  If the new sight is NOT the right thread, the hole can be re-drilled and tapped to the correct size.

The Express MIGHT be extracted intact.  IF not, the stub can be simply drilled out and the hole tapped.

Note that Remington sells luminous beads for their Police guns that are made to fit the factory bead base.

Remington has an excellent question section on their web site.  Post a question, and a Remington rep will answer.
remington.custhelp.com/cgi-bin/remington.cfg/php/enduser/std_alp.php

Here's what a quick search turned up:

" What is the tap size of the front bead sight on the 870, 1100, and 11-87?

Answer
The thread size of the ivory bead sight on our blued finish barrels is .146x48. A replacement front bead can be ordered direct from the factory by calling 800-243-9700.

Brownell’s also offers Remington Parts. Their web address is:

www.brownells.com

Some models have a front sight that is pressed in. Contact our Parts Department at 800-243-9700 if you need technical support.  

Something like the XS Big Dot might be good for the Express if you can not use the Trijicon since it epoxies over the bead.

870P is threaded 6-48.  I have a Meprolight tritium bead from Brownell's on mine.  870 Express is pressed in.  You will need to drill and tap, which might be better left to a gunsmith.  Actually, might be better off taking both to a 'smith.  That's what I did with mine just 'cause I don't have a drill press and I was concerned about breaking off the bead and having to drill it out.  A tritium bead on an 870 is a great sight.  For home defense, I think it is the best.

+1 on the XS Big Dot sight, if you can live with the fact that it is glued on (I used JB Weld on mine). Looks like a factory job when it is on and the big tritium dot is easy to pick up.

http://homepage.mac.com/jgregjones/.Pictures/Shotgun/870T03.jpg

Quoted: +1 on the XS Big Dot sight, if you can live with the fact that it is glued on (I used JB Weld on mine). Looks like a factory job when it is on and the big tritium dot is easy to pick up. homepage.mac.com/jgregjones/.Pictures/Shotgun/870T03.jpg

Could we get a couple more pics of that front sight? Like from the top and an actual sight picture? Thanks!

Since I posted this, this exact topic has repeated itself twice - the marble sight, 6x48 thread, etc.  Can we get a sticky on replacing 870 bead sights?

Quoted: Since I posted this, this exact topic has repeated itself twice - the marble sight, 6x48 thread, etc.  Can we get a sticky on replacing 870 bead sights?

One of those threads is probably mine. I just got my 870P today and a Marble's Tritium 6-48 sight is already en route from Brownell's. I hope to attempt the install this weekend and if I do, I'll report back on how it goes.