Are you talking about the locking lug that engages the barrel release? Or a sling attachment lug? The factory T-C Contender barrel locking lugs are electron beam welded. TIG is acceptable if you are willing to risk the likelyhood of bore distortion and decreased accuracy.
Silver solder, in my opinion is a very "iffy" marginal proposition, especially in a muscular caliber. For a sling attachment lug, silver solder, or even soft solder is fine.