F5MFG MP5 50 round drum mag has been in development and testing for over a year. We’ve found that mag well dimensions vary from different manufactures just enough to make a precision machined part fit loose in one manufacturer and tight in another (HK for example). Given this scenario, we’ve overcome this obstacle to make for reliable feed/function thru an adjustable shim system.
A tighter fit vs loose (loose being 1/8″ max front to back play) is required for reliable feed.
Insert magazine in mag well and observe fitment, the aluminum shim is malleable and witness marks will be visible (normal). This can be considered part of the wear in/break in procedure. If too tight, the shim can be adjusted by peeling back one of 6 layers that are .003 thick to achieve desired fitment.
The procedure for removing layers of aluminum shim are accomplished by using a razor blade to pick up an edge or corner of the material and peeling it back. See attached link for reference – http://www.accutrex.com/accupeel-laminated-shims
Shims are replaceable if needed.
Compatible with these Models
Heckler and Koch
Zenith / MKE Firearms
Please note that we can not guarantee fit with out of spec clone firearms.