Hi, i wrote this a while ago; http://www.network54.com/Forum/67044...nd+performance But remember that a sporter spring works well in a 30's standard. The Knibbs 2 spring set I had bought in the past for this size gun had the correct (or close) gauge wire and number of coils, but the spacing of the coils was very open and they did not work as well as original, as well as being about 2 inches too long in total
I was lucky in that I had some NOS BSA ones and used those in the 45" guns I re-sprung (both single and twin sets) but the data above is all I can find I am afraid.
So Airsporter I think will work, am not too up on currant Knibbs / Chambers / Protek versions.
A good Sporting will exceed 600 fps with Wasps or H+N ftt, so chrono yours as these are the most powerful BSA design!
ATB, Ed