that or if it actually does use aps type springs there are two kinds, there are 11mm ones that use a 7mm spring guide (i think that was wht u meant when lookin for a 7mm spring) or there are the 13mm springs that use the 9mm spring guide. If the 9mm guide will fit (it should cause its only the shaft thats bigget the base is the same) you have a wide range of lower power springs to choose from, tho i think that would start gettin expensive especially if you think the aps spring would still need to be cut cauee its too long.
http://www.x-fire.org/etop/bolt_sp_thicker.html
try checkin the length of the spring amd see if you can find the length of the aps springs to comfirm itll fit.