After working tirelessly to find a reliable lockback solution for the double stack platform, Atlas Gunworks finally hit the nail on the head. The Atlas Gunworks Overpowered Spring is the perfect solution when used in conjunction with the Atlas Lockbak Follower, and a lockback slide stop (follower not included). Made to fit 120mm and 126mm. Available in both +15% and +18%, the 15% works best with 120mm/126mm magazines, while the 18% spring works best with 126mm/140mm magazines. Mfg: Atlas Gunworks