Very low FPS with my Modify M24

So, brand new Modify M24,

Out the box, stock (I'm assuming id a 50 because of the color) 50 D bucking and stock spring the FPS, w/ .20s is 425 FPS.

- Stock Spring 70 D Bucking 430 FPS.

- M150 Spring 70 D bucking 437 FPS

- M170 Spring 70 D Bucking 437 FPS

- M190 Spring 70 D Bucking 447 FPS

Every other sniper I have had with a 140 spring I get 500-515 FPS with a 70 bucking, ASG SSG, Sportline MA, JG/ Double bell BAR and TM even the cheap JG M700. With a m150 Spring I get 530 + and never have had to go past that to get 100 Yards with.40 BBs.

This very pricey sniper is driving me crazy. I have checked for leaks and I get the bolt to stay back the bucking is not out of place.

I'm beginning to think it's a volume issue because of how thin the cylinder is but but hey, I'm not doing math to verify my assumption based of a comparison to the other platforms I mentioned.

Any ideas would help, I will fidget with it more and see what I can get.

As a back up, any ideas on what HPA will fit in this bolt system would also help.

Thanks