G21SF w/ Picatinny and Ambi

[nick425]

Fixed... It was my damn thumb holding it down...

[JR]

There are only a few things that can cause this failure. You decide which one.

1 Directly involves the slide lock. Installed incorrectly (re-install), weak spring (replace unit)
2 Directly involves the magazine. Need an up-dated follower (replace unit), weak mag spring (replace unit)
3 Weak ammo. Fails to blow the slide back far enough to engage the locking notch. This is an issue with some 9mm pistols, pretty much impossible with the power of a 45.
4 Shallow slide notch cut. (re-cut the notch)