As an FYI, Wolff makes a single spring in two different weights.
Recoil Springs for the Mustang and the Pony, like the Officer's Model, are high performance, single recoil springs to replace the dual spring factory systems. These single springs offer improved reliability and smoother functioning than that found with dual spring recoil systems. Each load-rated recoil spring pak includes an extra power firing pin spring.
42811 COLT MUSTANG/PONY .380 STD RECOIL SPRNG 11LB
42812 COLT MUSTANG/PONY .380 XP RECOIL SPRNG 12LB