If you're wanting an fps boost, I'd suggest the spring guide for a slight fps boost and a tightbore.
I've been experimenting recently with
Tbb's:
I have a tm aug high cycle and didnt want to destroy the tm magic but wanted an fps boost from it's out of the box 265-270.
It came with a stock barrel of 260mm. I swapped for a zci 340mm and got a 30fps boost; now chrome's 298-302.
If the mk18 has a 275mm standard barrel, you could potentially upgrade to similar barrel length based on the piston, just dont go over 350mm or you will need a different ported cylinder and that would mean gearbox work. I put a Prommy 363mm in my stock tm scar H, expecting a 20-30 fps boost and got no change at all, I beleive that's because the inner is too long for the piston and so there is a drag effect on the bbs and it negates the gained fps from the longer barrel.
In theory, new barrel and the spring guide could give you up to "not guaranteed" 20-30 fps boost that shouldn't add any stress on the gearbox. Please someone correct me if I'm wrong!
Tl;dr - I might not understand airsoft physics so ignore me!
I've been experimenting recently with
Tbb's:
I have a tm aug high cycle and didnt want to destroy the tm magic but wanted an fps boost from it's out of the box 265-270.
It came with a stock barrel of 260mm. I swapped for a zci 340mm and got a 30fps boost; now chrome's 298-302.
If the mk18 has a 275mm standard barrel, you could potentially upgrade to similar barrel length based on the piston, just dont go over 350mm or you will need a different ported cylinder and that would mean gearbox work. I put a Prommy 363mm in my stock tm scar H, expecting a 20-30 fps boost and got no change at all, I beleive that's because the inner is too long for the piston and so there is a drag effect on the bbs and it negates the gained fps from the longer barrel.
In theory, new barrel and the spring guide could give you up to "not guaranteed" 20-30 fps boost that shouldn't add any stress on the gearbox. Please someone correct me if I'm wrong!
Tl;dr - I might not understand airsoft physics so ignore me!