Good luck with finding clubs in Lancaster County that shoot ATA. You'll find plenty of places to shoot practice but very little ATA register.
Palmyra, Southern Lancaster and Conewago located in Elizabethtown are the only three that shoot any kind of register shooting on a very limited basis.
My two favorite places to shoot in that area would by Palmyra and Columbia Fish and Game. Palmyra is probably the most ATA oriented. Columbia has good membership base and a good turn out of shooters on their Wednesday night practices.
Listed are the trap clubs that I have attended the most during the last four years I worked in Lancaster county.
Manheim Sportsman,
Conewago Rod and Gun located in Elizabethtown,
Cocalico Sportsman,
Palmyra Sportsman,
Columbia Fish and Game,
I never had the chance to shoot at Southern Lancaster. Hopefully some day I'll make it down. With working in the Lititz area the other clubs are just a little easier to drive to
Dale,