Yes it's just like the chamber for the L96 in that regard and it has been assembled correctly with no bumps or anything in the hop up rubber, in regards to perfect compression what would be the best way to achieve that in this style hop up?
Well, to ACHIEVE perfect compression it's mostly up to the design of the parts and materials used in construction. The only thing you can do to try to improve compression is to:
-use a better fitting O ring on your piston (that's going to be up to you to decide what fits or works best)
-use a better o ring lube, or
-use teflon tape on select positions of the internals (cylinder threads, front of the bucking, etc) to help seal it against leaks.
Do not automatically assume that you need teflon tape, nor that using teflon tape when not needed won't hurt performance. I've found that teflon tape helped compression in my stock cylinder, but it actually hindered performance in my PDI cylinder. PDI tolerances are very tight and precise, so I didn't need teflon tape. That's not me bragging; I am not brand or type myopic, and I don't think PDI is the only quality parts provider, this is just my experience.
With the compression check, all you do is remove your receiver from the outer barrel and stock (body) of the gun. You should have your cylinder, it's internals, the trigger, and the nozzle all still assembled together in the receiver. Cycle the bolt, return it, and put your finger over the nozzle tightly. Pull the trigger. The objective here is to see if you can keep the now pressurized air in the cylinder inside for 60 seconds. If you release your finger after 60s and you hear the piston hit
the end of the cylinder, that's good. Merely hearing a puff of air isn't a good enough indicator.
To test your bucking's air seal, simply assemble your gun completely, remove the magazine, cycle the action, dry fire once in a safe direction
to clear it, then cycle and dry fire again with your finger over the end of the inner barrel. This will test your bucking / chamber for air seal. If you can go for 15 seconds or more, that's good enough (in my experience). If, after 15s you hear the piston impact the cylinder head, you're good on air seal. It will be harder to hear the impact since there's less pressure due to the included volume of the inner barrel when you're holding it closed.
Don't be discouraged if you don't get the 15s on the first try, sometimes the pressure has to build up over a few tries to push your bucking around to make it fill tiny, tiny gaps.
EDIT: also, don't ever lose that silver collar that goes around your inner barrel and seats up against the hop up chamber. It's instrumental in keeping the front end bucking / hop up chamber air seal flush and proper.