[Xenophobiac]

Here I sit, month 7 into my G3 build, and I have just borrowed a welder to get my trunnion set into the receiver. Here's the catch: it's a wire feed MIG welder without the gas. Can I use that to get my trunnion welded in? It's a demilled trunnion from RTG. If so, can I also use it to weld on the cocking tube, hanger, and scope rail? Also, this may be a bit naive, but can I get away with headspacing before welding, as I do not have a fixture for holding the receiver in place without crushing it. Or could I weld it in, and use a slap-hammer of sorts to get the barrel headspaced? The equipment I'm working with besides the welder is a drill press that does 3k RPM, an end mill, a bit for stainless steel (match barrel from HKParts), a finishing reamer, and a drill press vise. The 2 jaw hub puller worked for headspacing the last time before the first trunnion got messed up during drilling (long story), but that was with the trunnion not welded into the receiver. This may sound a bit confusing; I'm just as confused at this point, and any guidance is appreciated.

 

[jdonovan]

Here's the catch: it's a wire feed MIG welder without the gas. Can I use that to get my trunnion welded in?

Can you. Yes
Is is a good idea: F&%^ NO!

The right tool for the job is a TIG welder. I __MIGHT__ under desparate conditions use a gas shield mig, with thin wire on some of the thicker parts, but would never use flux core on any of it.

Or could I weld it in, and use a slap-hammer of sorts to get the barrel headspaced?

You should be using a hydraulic press. No a slap/slide hammer is not going to work well... if at all.

The equipment I'm working with besides the welder is a drill press that does 3k RPM, an end mill, a bit for stainless steel (match barrel from HKParts), a finishing reamer, and a drill press vise. The 2 jaw hub puller worked for headspacing the last time before the first trunnion got messed up during drilling (long story), but that was with the trunnion not welded into the receiver. This may sound a bit confusing; I'm just as confused at this point, and any guidance is appreciated.

It sounds like your shop is really not properly equipped to build this rifle correctly. I'm sure you can rig and boddger something that will get you close but its not going to be a nice product at the end of the build.

 

[Xenophobiac]

I was afraid of that. Somehow, I'm thinking this project will take quite a bit longer than I expected. At least I'm learning quite a bit regarding what not/to do, and the workings of the G3, so it isn't a total waste.

 

[jdonovan]

The H&K sheet metal guns are a bit of a challenge to make at home vs an AK.