As Claven2 mentioned they require a specific method ........I copied a lot of info from members on CGN and M-14doc / 45ACPKING in particular
From 45ACPKING
Gas System Unitizing.
A really FAST way of tightening up your groups.
We have to unitize this to prevent more rattling around of the barrel components. 2 methods are advocated in the US: USARMY drills and taps 2 screws (can't recall if they are # 8 or # 6) from the rear of the (annealed) front band into the rear of the STAINLESS STEEL gas cylinder, around the permanently immobilized spindle valve.
The second way is the USMC method which involves TIG (not oxy-acetylene) welding the front band to the STAINLESS STEEL gas cylinder body.
NOTE: Norinco Gas Cylinders are NOT Stainless steel but Chro-moly.
Oh yeah, clamp the 2 pieces together.... I emphasize that the gas cylinder is stainless material so that the experienced welders lurking in the group will get a "heads up" on the TIG. I've been advising my welder buddies to locate the relief hole "tab" and "tack" (just a little bit) on the front band. This is the vital operation.... Now the remaining tacks can be ABOVE the gas cylinder body, up in the surrounding barrel band at 1000 hrs and 1400 hrs.
Now take a round file and dress/clean off the alignment of the interior of the front band, hopefully the "C" clamp holding the front band and gas cylinder did not shift on you while welding.
I forgot to mention to anneal the front band (before welding) and bend up the steel "tabs" for the handguard..... Fat barrel soon to be located there. I use a pair of pliers for this one. Don't scratch the front band and if you do, file off the scars and touch up with Birchwood Casey's cold blue.
Assemble your rifle tightly with everything centered and as you want it once it is welded. Using a prick or center punch, make mate marks. Try to make the marks in the areas where the welds will go (10:00, 2:00 and 6:00). That way, they will be welded over and you won't have divots in your newly unitized gas system.
Disassemble the rifle. With a wire wheel, buffing wheel or sand paper, clean the areas around where the welds will go. Do a final wipe of the area with acetone on a rag. Clean, shiny metal is what you want to see. Any oxidization or oils will make your welds weak.
Mount the barrel (with or without receiver) pointing upwards in a vice. Ground the vice or bench, if it is metal. Install the barrel band and gas cylinder, lining up your mate marks. Clamp the two parts together with the gas cylinder lock.
Because the steel is a chrome-molybdenum alloy, it's a good idea to preheat (it's always a good idea to preheat) with a torch. Preheating burns-off oils in the metal, promotes penetration (a weld sitting on the surface may as well be caulk or bubblegum) and it reduces the likelihood of crystallizing the metal around the welds (which is where weldments usually fail). You don't want to melt everything together, you just want it warm. It shouldn't glow and the clean metal shouldn't change color.
Get some filler rod. Smaller diameters are easier to control and need less heat (smaller puddles). Big filler rods need more heat to melt and leave larger deposits. That means more heat on your barrel and gas system - not good. I used a 1/16" dia. ER70S-2 rod. It is specifically for joining chro-moly steels. If you don't have any of that handy you can use stainless filler rod. If you really have to, you can chip the flux off of an E309 stainless SMAW rod and use it.
Starting at 6:00, tack the joints in all three spots. Let it cool and see that it is straight. If everything is level, make three 1/16"x3/16"lg spot welds. Work quickly and make good welds, being careful not to put too much heat into the barrel and assembly.
When all three spot welds are finished, post heat with a torch, so that there is even heat in the assembly. This prevents warping from uneven cooling. Take some old welding mitts, aprons or any other rawhide and wrap the assembly around the weldment, this keeps it from cooling too quickly and warping and forming micro-cracks. Leave the barrel pointing upward as close to vertical as possible. Remember, the barrel took some heat and needs to cool too. By being vertical, the cooling will be even along the longitudinal axis of the barrel.
