I've used the Hatsan Vortex 44 grain pellets a long time and can see no difference in performance from JSB pellets. If you are looking for a deal on pellets, Field Supply has the Vortex on sale for $10.50 per tin and free shipping over $50. I think the normal shipping is only $4 and change anyway.
https://www.fieldsupply.com/airguns/ammo/hatsan-vortex-supreme-pellets.html
https://www.fieldsupply.com/airguns/ammo/hatsan-vortex-supreme-pellets.html