Reinstalling shotgun long mag tube springs can be tricky- here's a tip...video
Shotguns that have uncaptured mag springs require removal and re-installation. Removal is pretty straight forward - unscrew the cap/tube and the spring comes flying out. BE SURE TO WEAR EYE PROTECTION - you only get one set of eyes for life.
Getting a long spring back in can be difficult, frustrating, and a wee bit dangerous if the spring suddenly comes flying out. Here's a way to reinstall the spring easier and safer. The dowel I used in the vid is unnecessarily long, but that was the only length the hardware had and I haven't cut it yet - it really doesn't take one nearly so long.
Remember - use eye protection. If a spring flies out, it comes out with authority and it whips around all over the place.