I may be wrong but I think I read that the hw45 was first designed by Beeman as the p1. Weihrauch chose to put in a spring as it was pneumatic to start and so was born the HW45 as we know it. If you want power go for the HW45, if you want to do 10m target the 75 is fine. There is now the 45 star versions too with spring and target grip.