Air guns did have a few advantages, such as no powder smoke and usefulness in the rain. Also, once L&C’s air gun was pumped up it would shoot 22 shots quickly without having to reload. As you say, though, pumping up the reservoir was not quick.
Haven’t checked but there has to be a rechargeable electrical portable compressor that one can use in the field. Or an apparatus that allows multiple co2 canisters to recharge the guns compressed air reservoir. I’ve seen commercials on tv for portable air pressure tools that look like a cheap drill hooked up to a device which compresses air to refill a flat tire.
If not...someone could easily invent one. IMHO