It doesn't take much at all to develop 4g of impact force. A short distance plus a sudden stop is quite enough.

I've managed to do it in a couple of inches--weighing out stuff. Drop a bit on the scale and watch the weight momentarily jump a lot more than the weight of what you just added.

If what stops it has no give at all you'll get that 4g when the gun has fallen 4x the trigger pull distance.