Re: Lost velocity when going from CO2 to AIR ?
Its probably the regulator on the air tank. Its normal for air to be outputting less pressure than C02, but that does seem a little on the low side. Is the regulator on the tank adjustable or a low pressure reg? It might need to be turned up, either with shims or whatever depending on the brand (read manual). Its also common for the regulator on the air tank to need a couple hundred shots fired to be broken in.
Also, might as well make sure your bolt is right side up too.