what is louder 25 cal hercules bully or bt65 carnivore 30 cal

According to PA specs the 25 Hercules Bully is 75fpe 4 meduim high loudness vs BT65 Carnivore 30 QE SL is 75fpe and 3 medium loudness.

You are better off with a 30 BT65 Carnivore since you don't want to shoot at 1200fps (in 25) where the sonic crack past 1070fps will sound like a 22 Rimfire in 25 caliber if you worried about loudness.

You stated an $899 Hatsan gun so if it were me I would wait for a 30 FX Bobcat to show up on the classifieds (only buy from long time trusted members with many excellent references) it's a WAY better gun than any Hatsan. Also not as heavy nor loud with a much better resale value 75-79fpe and easy 100+ yard accurate too. They typically go for around $800-$900 on the used market. Origilally cost around DOUBLE THAT BRAND NEW FYI... No tuning necessary just shoot 44gr JSB or FX label 44gr through it.