Same as without one. If you do it right. I grabbed the cocking lever in one hand and the grip just behind the trigger guard with the other and used a "scissor" action.
Pump slowly or your pump with break faster. And it WILL break. Also, if you shoot it until it is very low in pressure, take breaks as you pump it back up to let the pump cool. Better yet, get a hand pump and use the probe to pump the gun back up if it is really low and ONLY use the built-in pump to top off after a couple of shots!
Best thing is to shoot no more than 10 shots (in the sweet spot of pressure) and pump it back up. Shooting it way down will not give you very good consistency, but will put MUCH more wear and tear on the built-in pump. My sweet spot was from about 2900psi to about 2300psi for about 10 shots, but I usually pumped back up after no more than 5 shots and usually after only 2 shots. I used the gun for pesting, not plinking or target shooting so 2 shots was usually more than I needed unless I had another pest pop up really quickly.
Look up the threads here or on GTA for the pump fix and do it NOW! The O-band (it is not a typical O-ring) that is in the heart of the pump will disintegrate eventually and leave lots of little pieces of itself all throughout the gun causing more problems if you leave it in.
The fix requires replacing it with 2 O-rings. As I said, look it up on GTA and there *may* be a thread on AGN about it too.
Good luck!
You may have to search for Nova Vista Freedom pump fix, but it may also have a thread for the Aspen as well. Don't know.