[Chris Fultz]

if there is a way for you to keep the rod end of the cylinder open (do not route the tube to the solenoid), your cylinder will extend much quicker.

with the cylinder plumbed to a double acting solenoid, the vent air (when you extend the cylinder) is restricted through the solenoid.

There are a few ways to do this from a system standpoint.

You can T in a line from the rod end of the cylinder. When you activate the "extend solenoid", also activitate this second solenoid, which is completely vented to atmosphere. When you want to pressurize the rod end of the cylinder to retract, close this solenoid so that the pressurized air on the rod end of the cylinder will cause it to retract.

The other option is to just let the rod end vent. You will get a very fast extension, When you release the pressure after firing, then small bungee cords can full the cylinder back. You can get these little cords at most hardware stores (they are like 1/8" diameter and 6"long).

I am guessing when you did your first testing, you did not have a closed system, so the air could easily exit the cylinder when you extended it.