If someone would just write a decoding book on what all the various model numbers mean, it would be more helpful than Perazzi's own website.
The decoding is really pretty simple. Functionally the only difference is fixed trigger/vs. dropout trigger. And the majority of the pieces interchange in those. Two basic styles of actions, and two different forend hangers. Big whoop, eh?
The rest pretty much comes down to what the one in your hands has in the way of conformation and whether or not you find that to your liking. Lippard doesn't really get into the T1/2/3/4 thing enough to make that clear and it's not all that complicated either. There's always someone around w/ free advice if there are questions about a particular gun hahahaha
have a day
Dr.WtS
