I know that non-rocket space launch hasn't been written off yet. There have always been fools who think they can defy simple physics and practical limitations of readily available materials. As I noted earlier, achieving escape velocity will require a muzzle velocity of at least 25,000 miles per hour. That's over 9 times the muzzle velocity of a .220 Swift. Of course, that is ignoring friction loss with the air... so unless your intrepid inventors intend to eliminate the atmosphere of the earth... or come up with a payload that won't immediately burn up... and also can withstand the G-forces of such extreme acceleration... then such an idea is sheer fantasy at best.
As far as the refinements we see in air rifles... it ain't all that much. In my lifetime, we've seen about a 300 ft. per second increase in velocity. The few people who buy those very expensive 1200+ fps models quickly find that they need to use ultra-light pellets to get that velocity. And then they also find that they need to use the heaviest pellets to stay under 1000 fps because of the instability and inaccuracy they encounter as they approach or cross the sound barrier.
We ain't talking a rejection of smokeless powder or other practical technologies here moses! But I have shot the vast majority of deer in my life with open sighted black powder flintlock guns. Hey, did you guys happen to buy one of those Gyrojet rocket pistols? If you can even find a box of ammo for them today, it will likely be worth much more than the pistol. And what a great defensive round! Why, it was almost equal to a .45 ACP if you could get your attacker to stay at least 25 feet away so it could reach full velocity. At 8 feet, it was about equal in kinetic energy to a .22 short.
