FYI most inner barrels typically have 0.5 to 0.2mm of play between the inner and outer barrel on AEG's. My buddy's MK46, I shit you not, had 1.5mm of empty space. It could fit a ptw barrel (10mm OD instead of 8.5mm OD).
They're toys, not professional training weapons lol
It's very typical for people to use teflon tape as a barrel bushing.
Anyway, I'd still go with the krytac, they're really impressive.