M.P.18,I performance using a Lanchester bolt/FP and main spring.

[Rekraps]

Better than the OEM recoil assembly by a mile! The OEM mainspring is just a tad smaller in diameter than the M14 recoil spring, and tends to kink and put pressure on the  bolt causing friction. So.... My C&R M.P.18,I is an original unit, modified by Bergmann in 1932 to a side mount, 20 rd stick mag gun. I replaced the OEM bolt, firing pin and mainspring with my spare Lanchester mainspring, FP and bolt. Dry fire went well, so I took it to the range today and WAMMO that thing ran like a scalded dog! The larger diameter mainspring (like a Swedish K) is the answer. I used OEM magazines (I was lucky enough to find 10 of them on GB... don't ask how much they cost!) and there were no misfeeds or failure to fire/extract. 

Since the original M.P.18,I firing pins, bolts AND extractors are matched to the gun by SN, I can now rest well knowing they will not be damaged.