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":

You can also take all of the slop out of the trigger by making

your own trigger bar. I used the back of a hack saw frame.

It's an easy mod and is totally reversable if you don't like it

but you will. There are plenty of other mods that make the

gun more reliable too. All on YouTube.

Already did it - but I did it using the existing bar, as I found it to be easier and faster.  I used some JB Weld to fill in the oblong hole portions and left only the small hole that fit the pin.  Zero slop and took about 15 mins (minus the curing time of the JB Weld).  Zero trigger slop or take-up.

The mod for taking apart the non-serviceable bolt to try to adjust the spring tension for the ball bearing to hold the OEM charging handle in better...  nope, nope, nope.  It's 100x better to buy the MFI charging handle for many reasons.

I saw someone that cut the receiver cocking tube area a bit longer to make it look more like the real MP40 - but I am not about to cut into the receiver and remove that much material.

As for other mods...  you'll have to elaborate; not sure what else needs to be modded or fixed.  

I also did the spring mod for the bolt handle. Basically you use the

same detent ball but use a cut down 1911 mainspring that adds a

lot more pressure to the detent and holds the handle more firmly.

I haven't had any problems since doing that mod. If I remember correctly

I cut 5 links off the 1911 spring. I like the new bolt handle you installed

and I really like the take down screw. I might order those.

Thank you for sharing your pictures.  I just completed my MFI upgrades as well.  In one picture, your stock looks in the correct position.  May I ask, how did you accomplish that?

It's simply not "locked" in that pic.  

Thank you! I missed that.