from the horse's mouth
"What are the differences between the M-870 Police and the M-870 Express HD? (Ref. #000403-0000)
Description:
Can you tell me the main differences between the 870 Express HD and the 870
Police Model (assume that the 870P is one with a synthetic stock and front
bead sight). Are the 870Express and 870P receivers different at all, that
is, other than the differences of inscription ("870 Police Magnum" or "870
Express Magnum")?
Solution:
Structurally the two receivers are identical. The only difference will be that the Police model will have a more durable finish. The magazine tubes will be slightly different. The Model 870 Express HD will have two indents in the magazine tube to accommodate the new style plastic magazine spring retainer. However, this prevents the HD model from accepting a magazine tube extension without alteration to the tube.
Other differences will be that the Police model includes a blaze orange follower, sling swivel studs, a shorter fore-end, heavier shell latches, a heavier sear spring and a heavier magazine spring."
