Like “oil” and “Powerplant” threads, this will probably start a huge debate… nonetheless I use RG45 for acetylene on 4130 – why, it was recommended to me years ago, seems to do all I could ask and I have a large supply of it…
I am not a professional welder, I’ve never seriously thought about becoming a professional/certified welder -- I do envy the work the pros can do, but I don’t know any professional welders personally, so take this with a grain of salt.
"RG45 is a general purpose, copper coated, gas welding rod used for welding low carbon steels up to ¼” thick. It is a great selection when ductility and machinability are most important. You do not need a flux when welding with this product. This product is embossed on both ends for easy identification."
I always used commercial grade mild steel rod for 4130. My parts always passed all the lab tests. I talked to a long time A&P the other day who insisted that you need to use 4130 rod. You do not. Unless you can heat treat it afterwards, it leaves a fairly brittle joint. The low carbon mild steel stuff makes for a better joint in most applications.
The nearest welding supply is 60 miles from me so I did some practice welds with what I had, coat hanger and Er70s2. I took my samples in to the guy who does the annual on my J3 and he liked the coat hanger weld the best,LOL.
The welding supply shops did not have any RG45 but I was able to order some in for later in the week.
My A&E gave me some RG60 and some 4130 to try out I don,t like the RG60 it does not seem to flow out very well. The 4130 is strange it almost seems plastic, it welds nice and has a good looking bead
I use ER70S6 because TM Tech thinks it is the best for non-heat treated joints in 4130 airplane tubing. It is mild steel rod with more deoxidizers, and it works very nicely for me on both mild steel and 4130. YMMV.