Pastor Doogie wrote:Is it likely that the increased/ new spring tension from the sear, and the carrier latch spring were upgrades intended for 12 gauge only, and not a good idea for a 20 gauge like mine?
For me, this gun is about breaking clays, and defending the home when necessary. I thought a heavier trigger pull weight might be an advantage on a defensive shotgun, and that a heavier carrier latch spring might prevent problems feeding.
The heavy sear spring isn't going to affect feeding, and it's a good thing to have in a HD gun. For clays it's not so great, but it's easy to change. I keep a heavy sear spring in the gun at home, and change it out for a lighter one when I go trap shooting.
On the other hand, replacing the 870's carrier dog follower spring with the heavier carrier latch spring from the Remington 1100 was probably a pointless modification for you. I still think your issues were caused because you had something put together wrong, but even so, you'll probably be better off putting the original carrier dog follower spring back in. It's not an issue of compatibility - the 20ga 870 uses the same carrier dog follower springs as the 12ga - it's simply that this is a largely over-recommended modification, usually made by people who don't understand what that spring does, and how switching to a heavier one will change things. They just hear that the heavier spring is used in Police 870s, and assume it must be better for everyone.
A heavier carrier dog follower spring will not make the carrier raise a shell any faster or stronger, because that's not what the spring does. This modification does not replace a "pump-action" part with a stronger "semi-auto" part; the carrier latch spring serves a different function in the 1100, the actual carrier dog follower spring is the same in both guns. It won't make the gun more dependable with heavy-recoiling shells; the spring isn't doing anything when the gun is being fired, and your average hunting load kicks harder than even a full-power LE 00 buck load anyway. All that spring does is hold other parts together so
they will engage and raise the carrier, and hold the carrier down when the action is closed.
Police guns see
very heavy use, and people's lives regularly depend on them being 100% reliable, even if the department armorer forgets to replace springs on schedule, or if the gun gets slammed around during a confrontation. Very few civilian 870s are used that heavily or treated that badly, and anyone who does put that many rounds through their gun either knows to replace springs and other wear parts at certain intervals, or to take it in and have a gunsmith do the same thing. The heavier spring will also make the action stiffer, and make the gun harder to load. These drawbacks aren't issues for a trained police officer in a gunfight, but it's an unwelcome change for most others.
Bottom line: an 870 is just as reliable with a normal-weight carrier dog follower spring
in good condition as it is with an 1100 carrier latch spring, and it functions more smoothly and is easier to use with the former. If the heavier spring worked better, Remington would put it in every 870 right at the factory; it wouldn't cost them any extra to do so. I tried the extra-heavy spring in my gun, didn't like how it felt, and replaced it with a Marine Magnum one (same weight, but more corrosion-resistant).
Every shell loaded by pump jammed between the carrier latch, the bolt, and the top of the barrel. (A real mess) The Forend seemed to bind at both ends of the stroke (I was not short stroking the shotgun). 
