I was told by my steel supplier that some DOM tubing begin as a welded tube. Some of the heavier wall tubes are obviously seamless. I was ready to order some 2.5" x .375 wall material for a golf ball size barrel until I found out it was a seamed tube. It was to have a 3.25" x .375 wall trunion sleeve at the breech end. I have since switched to 4130 chrome moly. Any thoughts on that?
Agree with George on 4130 being weldable, but make sure you do the required preheat and do it right. 4140 is just beyond that and is tougher to weld right. The issue is cracking and it's a good idea to have a certified or VERY knowledgeable welder do it.
We had a three moulds (for brake pads) made of D2 hardened to Rc60 go bad. Turned out to be a bad batch of steel and the supplier covered the costs - to the tune of several thousand bucks. Cracks showed up in first 10 to fifteen cycles of operation.
Thanks for pointing out the weld before drawing on some DOM. Let me point out that using the steel supplier as a resource is one of the standard industry practices - tap the vendor for all the information you can get.
AND, WELCOME to the forum! Looks like you're starting out on the right foot!