How difficult is it?  Whose 80% receiver did you use?  Just got a manufacturers license with a friend of mine and considering trying to put one together.  Only true builds from parts kits we have done so far are a couple uzi's.  Are we getting in over our head with the 42?

I watched @53gunner weld one back together years ago. I think he used all the original receiver pieces. It was mostly a Yugo M53 kit.
If he obtained any new replacement sections, they would've come from BRP but I can't remember.

You'll need to make or buy a jig to hold all the receiver sections in alignment (the full length of the receiver) as you weld, and you'll need to TIG.
It's very easy to let it warp if you aren't careful, so tack everything a little bit at a time, then go around alternating with you fill welds.

In the end you'll be grinding, polishing, deburring, and truing it up everywhere to get the bolt to slide smoothly. The better your alignment is during the welding, the less work that'll be.

Doesn't sound overly difficult.  The kit I am eyeballing is an M53 kit as well.  Planning on a .308 conversion.  I just registered over on weaponsguild.  Tons of info over there to dig through.

Or you can just do it by hand tacking it on and checking. Jig is unnecessary.

You don’t need tig. Mig is fine.

The hardest part is riveting the rails on, and getting a good wed that penetrates inside but doesn’t protrude inside jacking up the action. It’s nearly impossible to grind out excessive weld on the inside.

The semi auto parts are almost as expensive as the entire parts kit if I recall. You’ll need a semi auto bolt, grip stick, and FA denial bar.

I don't think he'll need those either.

Well shit then you’ve really got it easy. Less cutting and welding. Go for it.

Inthinknwe are gonna give it a go.  Might be a few months, but we will post pics.

Howdy, it’s not overly hard and you don’t really need a jig but I highly recommend it. Hell you can build one for about 15 bucks so why not.
Doing it with a complete cut receiver is a great way to start but you can use BRP shells. The shells need a ton of work though. Rail riveting is pretty simple so long as you have a river backer. I think it was Robert rtg that sold em. If you can’t find one you can make it for a couple bucks.
Make sure the canning piece is a matching numbers set!
I was gonna suggest weapons guild it’s a great site! Also check out MG42.us.
If you have any questions feel free to hit me up

I built one 15 years ago or so.  If you just take care to line everything up when welding and take your time you'll be good.  Semi autos can be finicky to tune but building it FA will get you past that.  As was mentioned already, careful of excess weld inside receiver.  There isn't much room to reach in and clean it up.

Thanks guys!  I may message you when this project begins.

Yeah no prob man

Its not that hard. A jig is easy to make with allthread and unistrut.  But keeping it straight is the biggest thing to keep in mind.

And the results are well worth it!

If you are gonna do a .308, consider building it from the beginning with a MG3 recuperator and buffer.

You can back up the gaps on the inside with copper.  Weld won't stick to it and it should keep the bead from protruding into the receiver.

Good tip. Thanks!

I started my MG42 semi project many years ago and the one thing that constantly was a pain in the keester was not the welding (I actually used a flux core welder with flattened copped pipe backing) was the area around the cocking handle slots (worked out fine BTW)... Tough with my welder, but doable... Several times, I needed to cut out the entire area and reweld the cocking slot at the back end of the receiver. I used all original M53 receiver pieces with no problems at all. The best way I found to reweld the back receiver chunks was to use the original rails included in the kits as a template (use threaded bolts to secure the rails to the receiver chunks) for spacing the chunks of the receiver correctly. After all of the welding is done, then remove the old rails and install the cheap new ones.