K1 vs K2 Differences?

The original K series rifle used dual CO2 cartridges. The first cartridge would go in nose down as the current K2 does. Then a second CO2 would be inserted in backwards. This would allow for two CO2 cartridges to be used. This version was problem-matic and could not be easily depressurized, and would not pierce the cartridges at times.

The original K series and K1 used this dual cartridge setup, but eventually gave way to the single cartridge in the K2.