Is there any other way to make an 870 express accept tube extensions, other than pressing, drilling, or filing out the dimples? Is there any way to order a new "police tube" and just install it? I dont want to rig anything if i dont have to.
Brent is correct. The magazine tube is a factory installed part on the 870.
Just drill them out and dress the edges with a round needle file. The holes will not be visible once the barrel is installed as the barrel ring will cover them. Otherwise, use a dremel and a sanding drum bit and go to work from the inside. I've done both and both came out well. No long term risk to the gun. I do not recommend using the "socket method" that some propose to press the dimples back out. too easy to screw that up and knock the mag tube out of round.
See above where the mag tube isn't user replaceable..........
IMHO it's best to leave 'dimpled' Express guns alone. The plastic piece the dimples hold in place retains the magazine spring, and also keeps the magazine cap tight. Now if you're never going to use the gun as a sporting gun again, I suppose it would be no big loss to drill out the dimples and negate the use of the magazine cap detent. But it will be necessary to jury-rig some way of keeping the magazine cap tight if you ever go back to the standard magazine.
If you want an Express with a magazine extension, best bet IMHO is to buy the factory version from the gitgo instead of trying to jackleg something. You get a good magazine extension into the bargain that way. Or buy a used, older version of the Express that doesn't have dimples to start with.