you have rubber seals inside your gun, when co2 is compressed it goes cold...
so when you start to walk or ramp with co2 it makes the internal seals freeze and crack and eventually ruin the gun....
Hpa is room temp when compressed so it doesn't harm the gun
you'll
actually find that co2, like all other gases obeying the laws of physics, gets
hot when compressed. Its the sudden expansion that cools it down, which also applies to air, but to a MUCH lesser degree...
The reason shooting slowly works is because the co2 expands (becomes cold), then has time to warm up before it meets the seals and other bits. By shooting fast, you're decreasing the time to warm thus it comes out cold. And when I say fast, I mean like 6bps - I remember shooting my mates inferno on co2 and having ice crystals coming out the end