FPS boost when increasing hop?
 

Question for some of the gun docs in here. Running my hopup completely off nets me 350fps on 0.20g, however turning it on slightly, basically to what I normally run it at on 0.28g, but still chronoing on 0.20g BBs it's netting me 386fps.

Gun in question is a G&G RK74 CQB. Hopup forward is completely stock. In the gearbox I'm running an M100 spring, SHS tappet plate and aluminium and it nozzle with o-ring, piano wire 9lb test tappet return spring, A1A Type D ported cylinder and silent double o-ring aluminium cylinder head, Madbull PX-02 piston and Modify ball bearing aluminium piston head.

The gun chrono'd the same way albeit less FPS before I toyed with the gearbox compression components.

Would it be a bad air seal at my hopup with the hopup disengaged?

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This is normal, you need to chrono with hop-up turned on. The hop-up keeps the BB in place, and when you shoot, it won't move until there's enough pressure to move past the hop-up, giving you increased FPS.

With the hop turned off, the .20s are leaving the barrel before they've absorbed all the energy from the compressed air.
With the hop on, the air builds up to a higher pressure before the BB starts moving, allowing it to accelerate faster.
It's an effect very similar to joule creep, and it's why chronoing with the hopup off is dumb.

If your setup is significantly overvolumed, more hop up allows higher pressure to build before the BB is released from the chamber.

Makes complete sense. Appreciate it guys.

I purchased the new cylinder to match the stock brass cylinder in terms of porting (3/4 port). Barrel itself is 233mm. I've seen mixed reviews of people running 3/4 ports and 1/2 ports on barrels this length (MP5 @ 230mm).

Would you suggest swapping to a 1/2 port cylinder or throw in an M90 spring for the time being?

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If you only ever shoot .2g, use a half port. If you use anything heavier, use 3/4.

I normally shoot 0.25g and 0.28g.

With that said, it looks like my best course of action would be to keep the cylinder but drop the M100 And throw in an M90.

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