I'm sure that there is nothing I could possibly write that could be of interest to you, so, I won't even try.
For anyone else interested, these parts are made to a universally accepted standard which can be found here:
This spec clearly shows, contrary to popular myth, that the outside threads are not tapered at all. The outside threads are absolutely straight, just like a NPS fitting. The taper refers to the inside thread where the thread become less deep such that when screwed into a 1/8" PT female fitting it will tighten up. If the outside threads actually tapered it would require some sort of strange tapered female fitting.
I used NPT fittings all the time when I worked in an inspection area which had equipment that required an air supply. You put some teflon tape on the end and wrenched the fitting tight. These NPT fittings do not go into a tapered hole. NPT fittings always go into a straight cut hole, just like the fill head on the Crosman.
For use on the Crosman bulk guns, the key specification is L1 (handtight engagement)
L1 is the length of the NPT thread that will screw into the female fitting to hand tight. For 1/8" NPT L1= .1615" So, as long as the engagement needed to compress the washer in the Crosman fill head is less than .1615" then a NPT fitting will work just fine. As I recall, in actual tests it took less than .100" engagement to get a NPT fitting handtight on a Crosman fill head.
When this issue came up some years ago, I thought it was weird because I had already knowingly used standard 1/8" NPT fitting on the Crosman guns for at least 20 years without a single problem.
Plus, If you look at the nipple of a Crosman bulk CO2 tank, you will notice that it is a NPT thread.