First of all, I prefer rivets, and do not care to do any welding on my receiver. However, there is "more than one way to skin a cat", and if folks prefer to use screws or welds as an alternative means of assembly then so be it. Apparently these other methods do work, hence the interest in utilizing them. The question about welding posed by bulletslap really didn't address cost issues but rather which welding process would be the better choice. As a welder myself in an industrial environment, I feel that I can offer my opinions from a more technical aspect rather than which one is cheaper. First of all, there is nothing wrong with MIG welding as it relates to this particular project. With the proper constant current/constant voltage setup, the proper slope adjustment in relation to the wire diameter will enhance the quality of a MIG weld. My reasons for preferring TIG has to do with the DC straight polarity setup, which allows for more penetration due to the increased allocation of heat at the positive pole, as compared to MIG welding. If the welds are to be ground smooth, you'll have a much better weld joint with a TIG weld, as most of your weld will be intact instead of being ground off. You are right; I doubt that anyone can tell the difference between the MIG and TIG weld after grinding smooth...it's what's beneath the surface that counts. Something else to consider...some receivers may be hardened in which case you may want to avoid welding altogether. Steel that has more than .30% carbon can harden excessively around the weld area, causing brittleness and subsequent cracking. Additional annealing procedures would have to be utilized in addition if hardened receivers are welded.