Hi Don, Paul has great advice (as always) you said “I have used a screw driver to hole the spring down” I dont think you should have to hold down the mainspring with a screwdriver it should, if bent around the arbor, automatically grab and hold with the tension created when winding. this is probably a dumb question but I did this once, are you putting them on the right way????? also are you winding them up on a mainspring winder or in the works??????? I also dealt with one that would not hold, it was because the end of the hole was tore and the torn part was bent towards the arbor and pushed the mainspring off the pin……..but this one would release way before fully wound..I do on occasion have them “skip” when first winding up, I use a mainspring winder, but after it catches and I wind it up fully and carefully the issue goes away, maybe its the air up here 
as Paul mentioned @Arutha wrote:
If all looks good you need to grab the inner end of the spring and bend it into a tighter c shape
and the end of the mainspring curls around the arbor enough then the next coil will hold it into place and it should not let go, anyway, just me thinking out loud, let us know Don.
P.S.Does anyone have access to a chart that would give original mainspring sizes for specific clocks, It sounds like Lou at mile high clock supply is putting one in his new catalog which is coming out soon but I would like to gather as much info on that as I can.