They come with 6.04mm ID inner barrels with a 10mm OD, and have since Sept. 2006, all models.
I can adjust my hop up to make it perform poorly, too.
Funny, after about 45-50K rounds at 420 fps, I haven't had to change my $3 hop-up (US retail), nor done anything but clean the barrel a couple of times per year. But I did do a 2008 version up kit for them, since I virtually gave away my boards to fix other guys' messes. I wouldn't call that an "upgrade" though, rather the cheapest way to get the most parts.
I have yet to have any AEG, stock or heavily upgraded, that lasted as long, and didn't require alot of work. And I've had alot, no clones either.
Age verifier Northern Alberta
Democracy is two wolves and a sheep discussing what's for dinner.
Freedom is the wolves limping away while the sheep reloads.
Never confuse freedom with democracy.