Cant remove end cap from S200?

[HW90Guy]

Yes, you can get an adaptor to fill the cylinder off the rifle.

I meant is it ok to remove the cylinder and fill it the normal way using the brass cup? I can't see how I can attach the brass cup while the cylinder is attached to the rifle without scratching the underside of my barrel. Maybe my brass cup is a large size, although I assume they are all a standard size Also I think the T bar might be a bit funny as even if I could get the brass cup on and twist it, the hole on the cup and air cylinder wouldn't line up

Thanks for the rest of the info! Going to give it another go. Maybe I am just being too careful