I like to collect WWII major powers long arms... but I don't have the pocketbook for the real full auto stuff, so I stick with semi-auto. For the MP40, that meant getting the much-maligned ATI 9mm version. I knew of the reputation going in: it has the basic MP40 look, but a lot of parts that aren't quite right, poor reliability and some junk parts. Either way, it was my only choice since I wasn't going to spend $4K on an DK MP38 clone that I've heard reports of having nearly as many function problems as the $500 ATI MP40P 9mm clone - and I didn't want the .22LR version.
Anyway, I went with the $500 ATI clone in 9mm. Got it used, function tested it (worked without issue - whew), but the trigger was HORRIBLE, the cocking handle would fall out at least once a mag and the overall look was... less than authentic - even to someone like me that wasn't well-versed in MP40's.
After some research I found a way to fix the trigger pull issue and cost was $0. For the charging handle, there wasn't much I could do. ATI was no help, but I did find that MFI has some MP40P parts. I've bought a LOT of stuff from them before for my SIG 556's, MP5's and I ended up getting several MP40 parts from them:
Front sight hood - cosmetic improvement that looks MUCH better and is period correct for the look.
https://mfiap.com/i-23899918-mfi-replacement-wwii-period-correct-front-sight-hood-for-the-gsg-ati-mp-40-mp40-mp38-price-includes-sh-via-1st-class-usps-insurance.html Knurled Safety disk/knob - cosmetic and functional improvement that looks, feels and functions much better than the stock one.
https://mfiap.com/i-23900027-mfi-gsg-mp40-9mm-22-lr-disk-safety-wwii-period-correct-price-includes-sh-via-1st-class-usps-insurance.html Cocking handle - very much needed as a functional replacement since this one won't fall out, and also is period correct for the look.
https://mfiap.com/i-23900013-mfi-gsg-mp40-9mm-cocking-handle-charging-handle-wwii-period-correct-price-includes-sh-via-1st-class-usps-insurance.html Muzzle Nut/thread protector - cosmetic improvement that is period correct. Also, much better quality.
https://mfiap.com/i-23899886-gsg-mp40-9mm-only-muzzle-nut-thread-protector-barrel-nut-wwii-period-correct-super-rare-russian-front-deep-slanted-groove-style-price-includes-sh-via-1st-class-usps-insurance.html threaded takedown pin - both a functional and period correct replacement. The OEM C-clamp pin was horrible for maintenance.
https://mfiap.com/i-23900026-mfi-improved-wwii-style-takedown-take-down-pin-for-the-ati-gsg-mp40-price-includes-usps-ground-select-8-75-off-if-ordering-with-any-other-product-with-sh-included.html Yeah, I spent ~$265 on parts for a $500 gun, but oh man were they worth it in the functional and cosmetic improvements. I also SBR'ed it and bought the ATI MP40 stock.
All-in-all, with the cost of the parts, tax stamp, stock kit, etc - I've turned a $500 gun into a $1K+ gun, but it works (and looks!) significantly better now and the common issues mentioned, like the cocking handle issue, the appearance, and the trigger - are all remedied now.
It goes well with my other WWII "SMG SBR":