I was getting a couple other things from tinmantech.com & I noticed they sell ER70S6 for welding 4130 instead of the RG45 that I have seen recommended elsewhere.
Since I was getting other stuff anyway I bought a pound to play with, this is what they say on the website:
"Our filler rod for 4130 Chrome Moly is NOT 4130 alloy. Rather, we offer what engineers, welders, and experience shows to be the best choice for welding structures of tubing and sheet: ER70S6. I know we recommend something a little different on the 4130 Airframe Video, but I can't help making little improvements as I discover them, or as they become available. So it is in this case. This filler has great penetration and little spatter, flows evenly, and is reasonably priced."
Anyone have any opinions on the difference between the 2?