As far as the original post and trying to figure out the failure to feed. As I mentioned before the extractor is worth looking at. I have a Kahr CW380 that had the same feeding problems so I slightly radiused the bottom edge where the extractor makes contact with the round and polished. I have never had a failure to feed since. As the diameter of the 9X18 round is slightly larger than the .380 the extractor will have an effect on feeding. I am hoping that will eliminate your problems as it did mine.
When I first got my G42 and was having ammo sensitivity problems with light bullets (the PolyCase 65gr Inceptors), I filed the extractor claw edge down a little and also the magazine feed lips.
With the Mak bullets being larger, it makes sense about the extractor binding. I ordered a spare extractor and will probably give it a serious filing.
Why go through all the trouble? Why make a perfectly good G42 into a freakish Frankenstein?
It's a fun hobby and I enjoy the process. The G42 isn't my primary (or secondary, or tertiary) carry gun. It might be for my wife down the road, but I'm hoping she'll opt for one of our small 9mm.
It's mainly because I'm curious and I enjoy learning about different firearms, components and cartridges.
If over the next few months of tinkering and playing, I can get a system in the G42 frame that is able to ballistically beat the Underwood +P 90gr 380 XTP with 100% reliability in torture tests, I'll be happy.
My first test will be seeing the difference between the Underwood 90gr 380 +P XTP and the Underwood 95gr Mak +P XTP. If the ballistics are pretty similar I won't work very hard to make the system work. If they're much better... then I will. But I'm not fooling myself into thinking it'll be better ballistically than any of my small 9mms that I usually carry. It's just for fun and education.
Looks like you have a perfectly good paperweight now. Why would you do something like that instead of buying a Mak for a bit more money. I understand the multi caliber aspect, but why else? Maks can be had cheaply if you look around...
Do you even read, brah?
Again:
I'll help you out. Hint: This isn't so much a Makarov pistol or cartridge thread as much as it is a G42 thread.