I've noticed alot of people having trouble with their Pump Mags in regards to their springs. Some of you guys may be using the Wave Springs provided by Smalley, however I have found in my own testing that this Wave Spring from Lee Spring Company is far more reliable. This is what I was using with great success in my old Chord Pump Mag before I foolishly sold it a couple years back.

Lee Part # LW 100 18 0250S

This particular spring adds another .5 waves per turn versus the Smalley. This simple change adds enough resistance to use a new Gold Main Spring with zero issues and no noticeable change to the pump stroke or reset. No more looking for a "beat to crap" or trimmed down Main Spring, plus it is stainless steel so it'll match your valve!

They work great but require a minimum order of 10, and @ $6.36 a piece that can get a little pricey - but you do have another option as far as Wave Springs are concerned!