You have to upgrade the units yourself. I use a heavier guage spring and a spacer to increase the guns tension. I also replace the inner barrel with a tighter bore one. I"ve gotten as high as 250fps on one of my guns (stock HL tank will shoot about 75-90 fps) I used to sell them on ebay (airsoft gun/lengthened barrel) so all you had to do was install the gun/barrel combo and you were off to the races.