Eric sez: "...Anyway, it took several pumps for full
velocity and fired .177 cal pellets (I think). It was quite accurate
and would put pellets right through a 2x4 when pumped enough...."

I've owned several "pellet guns" myself and have never pumped one enough to
pierce a 2x4, although that is (maybe) theoretically possible. As my old
boss used to say, " A word to the wise is superfluous"; and that would be
don't damage a fine air rifle by overcharging it. The limiting factor in
air rifles is not how much pressure they can be charged with but how they
are able to retain and release that pressure. Velocity is limited by the
valve which releases the "pumped" charge to propel the pellet. That valve
is actuated by a hammer/spring arrangement and accounts for vibration sharp
enough to damage scopes. Special scopes are made for air rifles that can
withstand the hammer effect. IOW, you may be strong enough to impart
tremendous pressure into an air rifle but only so much energy can be
delivered to propel the pellet. Larger valves are possible, of course, but
they adversely effect other things such as trigger pull and internal
sealing. That tremendous pressure has to be pushed by a piston and retained
by a seal.

Trivia: Air guns aren't new. Some went along on the Lewis and Clark
expedition 200 years ago.

Bob Swinney