For CA, add a spring (if you want a higher velocity) and a new piston, and you're golden. Personally, I'm up to about 40 000 rounds on my stock CA piston and no issues with it yet, but results with their pistons may vary. Nothing else required unless you push it up past 375 fps, then a harder type hopup rubber would be a good idea. I'd also throw in a bearing spring guide (which I did) just for better consistency. They already come with hardened gears and a reinforced mechbox, so there's really nothing else you need to do.
Unfortunately, as 'good' as KWA Armalites are internally, their mechbox shells suck ass. If you do go the KWA route, I'd strongly recommend a spring downgrade and a sorbo pad to prolong the life of the mechbox.
Last edited by Crunchmeister; May 11th, 2009 at 18:11..