Well, I have one of the older non-shrouded bbl Agents as a daily carry piece, and all I ever shoot in it is 158 LSWCHP +P.
Now, I don't shoot it very much at each session(kicks like hell with the factory grips, but they hide the best), but it's still tight after almost a thousand rounds over the years.
I'm sure it will loosen up eventually, but I'm not too concerned. With a little care it'll probably outlast me.