Barrel/hopup upgrade
 

ok, so i have a King Arms Colt metal M4 AEG. I replaced the 368mm inner barrel with a 363 Madbull stainless steel 6.03 inner barrel and i installed a Madbull metal hop up ( with the single adjustment gear). Now, as I fire, I seem to get a side spin going and I can't maintain a tight group (and yes I know proper firing techniques). Can anyone make a suggestion to what I could correct in the weapon to improve my groupings ??

You likely installed the hop up incorrectly or assembled it incorrectly. It could also be that you're using low quality BBs. It's too difficult to tell without more information.

Before doing any of this, obviously make sure the gun is not operable (battery out, safety on, etc.)

First thing I would do is disassemble the gun, and look down the hop up and barrel (with it apart from the gun, don't look down when it is assembled). Check to see if the hop up is centered. If not, that is your problem, center the nub and reinstall.

Your problem could also be an air seal issue. Disassemble the outer barrel and blow down the inner barrel with everything together. You should feel extreme resistance (like blowing into a straw with a closed end). If you don't feel resistance, then air seal is an issue. Fix this, and it could resolve your issue.

If you're using low quality BB's. Like Crosman or some other Wal-Mart/Canadian Tire no name brand, then this is likely the issue. Stop, spend $20 and get a bag of quality BBs, this should improve your accuracy/groupings