Testing out the 5V solenoid from SparkFun

Just got my 5V solenoids in the mail today, and seconds ago tested one on my power supply.  At 5V it seems like it will give a reasonable kick, but at 3.3V it is a little weak.  Not much I can do about this if I want to keep costs down.  I could bump up the voltage but then I'd need to add another LiFePo4 cell, which adds another $3 to the COGS.  The return spring is also a little weak.  I am worried that the mini slide for the recoil effect will bind, but there's only one way to find out for sure!