Drilling a tapping a CO2 fw/ a air fitting isnt allthat hard, or dangerous. Back in the late 80's these were all the rage on back bottle/back 12 gram guns. I made a few of them.
The trick is you need a drill press and the proper tap screw to get it right. You cannot hand hold the drill or the CO2 tight enough to make it.
Find one (as listed above) or go to a local machine shop.
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