Maybe a necro post, but I think this is usefull infos.
I'm working on a Ares M60 from a friend. It leaks pretty bad (170-190fps w/ 0.20g with a lonex M100, my VFC scar is pulling 390fps with this spring w/0.20g)
I checked piston head/cylinder head/nozzle compression (inside gearbox), I did the teflon tape mod on them so the fps went up to 210-240fps w/0.20g.
Then, I tried a no-name brand M4 nozzle to replace the ares stock one (M4 is longer than Ares' M60). I put some teflon tape around the external diameter of the nozzle getto style (stock ares' is larger) but now it's shooting 315-320fps w/ 0.20g pretty consistently!!!
But for the Ares M60 mk43, it would be this thing :
http://shop.ehobbyasia.com/ares-air-...-mk46-aeg.html
Edit : Yes, I also heard that M1A1 Thompson nozzle would fit (larger diameter) and trim down the total lenght. Let's take one with an o-ring inside!