I've got an 870 Express that I'm looking to upgrade. So far I'm thinking a new machined extractor to replace the mim'd part and a stiffer carrier dog spring like the police model has. Any thoughts on the sear spring? I see a "competition trap" spring (maybe too light for an hd gun?) and the police model heavy spring (maybe too heavy for a field gun?". Does anyone have experience with either of these parts?