For the basics, some other gun can work, but for really good focussed practice, it all has to be the same-- ESPECIALLY when practing the longer-range stuff for Pueblo.

With something as simple as a chair as the prop, you can do drills that exercise most of the Pueblo skills, e.g. shoot through legs ("port"), over top (low kneeling), off side of back (barricade) and then mix in the "bounce" - standing - s/k/s - and prone.