Systema Irregular-Pitch Spring M120S Stainless for all AEGs
http://www.wgcshop.com/pcart/shopper.ph ... S-ZA-06-04

Systema Irregular-Pitch Spring M120 Oil Temper for all AEGs
http://www.wgcshop.com/pcart/shopper.ph ... S-ZA-06-03

и если посмотреть http://www.airsoftcanada.com/SpringChart.html
то вывод прост: 120S - жёстче.