Hey, I have a 4130 receiver blank I screwed up on last year (misdrilled a hole). I buddy of mine just said, "I think I can weld that." He thinks he can fill the hole so I can redrill it in the right location. I told him about this forum, and he wanted me to ask you guys some questions:

Those of you who have welded on 4130 metal....

1) What kind of welders are you using? Arc, Tig, or Mig?

He has an Arc welder and a Mig welder. Another buddy of his has a Tig welder that he can use if that is what's necessary.

NOTE: Sorry on this next question; I'm not a welder (other than spot welding) and I forgot the term he used.

2) Q: What kind of "flux" [i think that was the term] do you use?

He is going to go buy the flux/sticks/coil or whatever, but was wondering what kind to go buy for the 4130 attempt.

Anyway, let me know.

And, as always, any info. is greatly appreciated.
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"If you want to be a fool, do what fools tell you to do"

"If you are going through hell, keep going." -- Sir Winston Churchill

I finished mine up last night with my gas MIG welder.  You can weld 4130 with no problem with MIG or TIG.  I wouldn't try Arc welding, the metal is too thin.   TIG is the best, then MIG, then Arc.  A TIG isn't necessary, just make sure to get good penetration with the MIG.

I'll answer the "flux" question about MIG because I don't have enough experience with TIG to know.  For best results and control with MIG, use fluxless wire with 75% Ar/25% CO2 gas.  Flux wire will work fine and just requires more cleanup (you're grinding and sanding smooth anyway).   You can easily weld this properly (well, properly enough to fill in a hole) with a very cheap "pocket" gasless MIG welder.  

If you have access to a TIG setup I would go with that.  As for the filler rod, use a 4130 vacuum melted low alloy rod.  This high quality welding rod is produced from vacuum melted material. This rod has ultra-low levels of oxygen, hydrogen, and nitrogen and is extremely low in trace elements. This rod is cleaner than standard rods and is the best available for 4130 welding.  However, we are not talking about the aircraft industry, which is where a lot of 4130 is used...any low hydrogen rod will work for what you are wanting to do.

If you have to weld a hole, will the welded spot take bluing okay?? I need to take a siderail scope mount off.  I thought of having the holes welded closed.

I want to use the correct finish which is bead blast and blue.  If the welds won't take bluing then I'll have to use rivets.

Yeah, it should as long as you use a rod that is designed for low carbon steel.  A lot of your alloy rods that have some nickel and chromium will not blue very well, if at all.  

Thanks!  I will check into that.

Quoted: I finished mine up last night with my gas MIG welder.

I don't suppose you could post pictures of your welds? I have screwed up my holes royally so I was thinking of having a friend weld my kit together for me.