[MultipleParadox]

If you have a metal 1 piece hopup handy, you probably should use that;

I don't know much about TM's stock 2-piece hopup unit but in general a 2-piece unit is most likely to leak air, so I wouldn't be surprised if the CA would perform better than the stock one.

Also, plastic hopups have some flex compare to the metal ones, which could cause some leaks as well under certain stress.

There's a reason why most if not all after market hopup units are 1-piece metal, I'd say!