Hop up problems with E1 Scar-H and C-Tac M4

[DropTheBomb]

Alrighty so I have two guns which seems to be having hop up problems.

First off with the C-TAC M4;
This thing has huge problems, air is leaking out of the hopup where the mag and hop up meet, double feeds like no tomorrow. Gearbox/air nozzle is fine, its apparently been having this problem for a while and i managed to get it working but then when i disassembled the gun and put it back together problem appeared again.
The hop up has a new 50 degree Lonex rubber and the hop up is a Pro-win hop up (not stock).

Echo 1 Scar-H;
Only problem ive had with this is the original hop up was engaging too much even when completely off, so I picked up a Lonex rubber swapped it and it definitely helped with the excessive hop issue but now on semi it double feeds every 1-3 shots. I swapped it to the original rubber and same problem, everything was perfectly fine before the swap. Did I just put something together incorrectly?

Lots to read but any help would be great!

[DropTheBomb]

Ok update to the issue, Scar is fixed and shooting great. Turns out the barrel needs to be pushed into the hop up very tight.

As for the C-Tac i did a test where i held the hop up against the gearbox and it fired beautifully so im now guessing its the hop up not being pressed against the gear box hard enough or the spring isnt keeping it pressed against the gearbox?

[Darklen]

ProWin AR hopup should have a long set screw where a spring would usually be. It hard sets the chamber against the mechbox, preventing movement.