[e-luder]

So far as I have noticed, adding o rings to compress the spring does have some effect. With the hop up unit fully tightened, the slide will not slide forward all the way, because the nozzle is getting stuck in the bucking. With 6 o rings on, the slide comes forward all the way (the nozzle comes fully into the bucking).

That's because the spring is stil applying "springing out" even when the slide is at rest. Your O-rings are not increasing the power of your spring, it's just causing the spring to be coiled constantly. Thus, "forcing" the muzzle into the bucking even when the slide is in battery.

With the hop up unit a little loose though, the slide comes forward all the way, hence the nozzle slides easily into the bucking. I don't have the plastic anymore. When I get my reaps, Ill try modifying my bucking so that it is a bit thinner on the inside, so the nozzle can slide into it, but I will have to be aware of a possible air leak. I just ordered a chrono, xcortech btw.

See, my concern with your modifications is that, it's not a necessary modification to begin with. Modifiying the bucking, I fear that you may overdo it and ruin the bucking altogether. In essence, the bucking needs to be tight around the BB to create a perfect seal. If you sand it down, you'll increase the chance of the bucking's inability to seal properly.

The fix to your issue is usually a stronger return spring and properly tucking in the bucking into the hop-up unit.

Should the bbh have no movement and be tight in the slide?

There should be no wiggling around. IT should sit tight.

Buy standard issue marui bbh, you mean the one that comes with the marui 17? Where can I buy one? And what nozzle would you say to get? Along with the nineball piston head.

I tend to use the Guarder ones but I stopped using them because they kept breaking on my gun at higher pressures. My Gun shoots at an FPS range between 370-385FPS and it obliterates the Guarder muzzle.

You can buy the Airsoft Surgeon kit. It comes with it's own piston head that's not half as bad as the other aftermarket piston head. It's a pretty good combo.

Or the Shooter's Design Kit. Those are the only three you should consider. Everything else is just crap...

Buy standard issue marui bbh, you mean the one that comes with the marui 17? Where can I buy one?

yes.
I will messege you the link.

I also polished my slide catch and my recoil spring to a nice finish. Is the guarder metal slide catch made up of material / paint that can be stripped and polished? the metal looks different.

That catch is made out of steel. Yes you can strip the paint but polish it right after to prevent it from oxidizing.