WE M16 GBB OB Hop up? Gas?

[Anthony]

Not sure if this topic belongs in this category. My apologies if it doesn't!

Hey all, my friend and I decided to switch to GBBR's recently and I chose the WE open bolt gbb M16 (hopefully some of you have or have experience with this gun). The gun is beautiful and hits pretty hard. The accuracy is great and the distance is pretty far considering that I haven't even touched the hop-up. The reason I haven't messed with it is because I can't figure out how to adjust it! I've looked online everywhere and even in the manual but I can't figure out where the heck the adjustment hole is! Is there anyone that can help me with this? Pictures would help a lot!

And for gas... The gun came with green gas/propane mags so I figured that's what the gun is built for. I've heard of co2 being to strong for blowback guns such as pistols and I'm wondering if it would be ok to use co2 with my m16, since there are co2 mags available and co2 is easier to find than green gas (not to mention less expensive). Propane is probably the cheapest but I just wanted to know what you guys had to say or advise since most of you are probably more experienced in gbbr's.

Thanks for the help!
Anth