I'm an amateur player and I don't practice regularly, only when I have enough time. I manage to practice several times a week. I have two student horns: a Holton cornet made by Yamaha and an older Reynolds Medalist cornet. Both seem to be in perfect working order with good compression. One is at the place I live(Reynolds) and another (Holton) at a different place that I visit from time to time. I notice a significant difference between how two horns affect my endurance. Reynolds feels very free blowing and tiers me up pretty quickly. Holton (Yamaha) on the other hand gives me some nice resistance and feels 'easy blowing' because of that. I can play it much longer and by the end of the practice session I can still -play- notes whereas with Reynolds by the middle of the practice session I can only -squeeze out- notes. Any idea why that may happen?