you wont go far wrong with a tx and viper scope. the vipers scb ret is great for hft. i have one on one of my guns.
i zero at 30 yards. that way theres an aim point every 5 yards on the ret. shooting a springer will also make you shoot with better technique. if you dont hold it consistantly, dont follow through properly or have a bad trigger attack, you'll miss. try and do the same thing every shot, it can be tricky if targets are put in awkward positions, which sometimes force you to hold it in a different way.
a lot of people struggle to shoot a springer well from the prone position, but it can be done. it is posible to give the pcp shooters a good run for their money. springers are great fun.