Sten bfa?

[browningautorifle]

a softer spring will give less rdspm or a harder spring will give more rdspm

To add to what Peter says...I've changed a few springs in my time. I was rebuilding an M3A1 Greasegun with new springs as it had none, used the inner butt springs from an FN C1 as I recall. The wire was thicker and coil heavier so it ran at about 1000-1200 RPM through it's 10 rds for test. I had to use a screwdriver to cock it. All were in the air at once... If you add a half a recoil spring behind the existing Sten spring you'll get an increase that will run about 750... There are trades though, ammo consumption, lack of manageability, lack of accuracy...post ammo letdown...