The mod is not very hard at all. If you have access to a drill press and a tap, your set.
i am sure the first to document the process was a fellow by the name of ALMIGHTY...
great guy and has groves of airsoft info in his head.
well, back to the job...
- remove the fill valve
- drill out valve position
- clean up drill job ( drill bit size determined by fitting thread choice)
- Tap for appropriate fitting ( 1/8 npt might be too big... try 10 -32)
- screw in instant fitting...( look for 10-32 instant fitting) ( PS, located here http://www.palmer-pursuit.com/cart/index.php?main_page=product_info&cPath=11&products_id=41
- and you should be fine...
the instant should be linked by a 1/4 or 6mm hose, and the hose should be capped off with a 6mm barb fitting.
that fitting i linked should work with all 1/4 or 6mm tubing. basically what the classic users use most ( some use 4mm or 8mm too)
since you are only running the gun at 125-130 psi or so, the guns are fairly good with co2... you might be able to get away with a stock mounted mini reg like the one i use on my 10/223.
Side note, I am not sure if the ACM m500 has a pressure relief valve, My Marushin 6mm did when i had it...be sure to plug it up with super glue/bondo/ JW weld... you dont want to experiment with higher pressure and have it all hiss out on you.
you can shoot us an e-mail at airsoft advantage and we can take care of that for you...