how do I hook photoflash capacitors in a series circut?

i am trying to build a larger coilgun with more volts, but am having truble hooking the 120uf 330v photoflash capacitors in a series circut. they don't charge, and when charged seperatly and connected in series, they just discharge eachother, leaving no power left.

The problem is you can't guarantee the actual voltage across the parts when they are in series, since the capacitance of these 120 uF caps may vary by 50% ! If you need more energy, better to add caps in parallel. Its a linear relationship unfortunately, but its probably the best way.
yes, i know that, i was just asking how, and even if it was possible to do this.