Sigh! I had Boone equipped with my Q-35 Matter Modulator, when I dismissed him using the console next to the elevator in the Lucky 38 in preparation to do the Render Unto Caesar quest chain. I also had and dismissed Ed-e at the same time. Without thinking I left Boone's equipped gear on him. After a night or two of gameplay and questing I re-invited him and found he was back to using his old rifle. No sign of the named gun anywhere. Not in his inventory, my inventory, etc. he did keep the armor he was wearing and several other items. Just the named gun disappeared.