You can improve reliability of your Remington 870 easily and for just $5. Remington 870 Police shotguns have different Carrier Latch Spring(Carrier Dog Follower Spring). It is from model 1100, the Remington part number F16966.

Standard Carrier Dog Follower Spring is silver, Remington 870 Police spring (from model 1100) is black:

Heavier carrier latch spring improves reliability and may fix feeding problems if you have them. The main purpose of this spring is to lift next round which comes out of a magazine tube. Remington 870 Police carrier latch spring (1100) will do this much better.

Remington 870 Carrier Dog Follower Spring (Standard, Police)

Remington 870 Carrier Dog Follower Spring (Standard, Police)

Tool which helps changing carrier latch spring:

How to replace Carrier Latch Spring (Carrier Dog Spring):

You can get heavier carrier dog spring here: http://tinyurl.com/kqug2b5

This upgrade is higly recommended. It is one of those upgrades which are not visible for others but improve reliability of your Remington 870 shotgun and not just for looks.