I've seen Reservoir Dogs a lot of times, and I recently read a book that dissected most of Tarantino's movies, but it's never come to my attention that he even switched guns.
Knowing Tarantino's work I'd say that it's entirely possible this is in fact a hint, or even a metaphor. Then again, this was his first full-feature movie and it might just as well be a continuity error.
In fact, I can't even find it among IMDB's 'goofs' for Reservoir Dogs. I might have to re-watch the movie to see the difference in guns. To be continued.
This page offers some insight in the guns used in Reservoir Dogs: