Gun retention seems to be pretty awful on your fingers, from my limited experience (2 classes) drilling on them. I'm looking into blue guns now and trying to think if there's anything to consider to make them less injury-causing. Maybe just cut off the finger guard entirely...
Or just don't put your finger in it I guess. Is cranking on a blue gun when someone's finger is in the trigger guard the equivalent on cranking an armbar on your training partner? I know it's ECQC and everything but it seems like basically intentionally breaking your classmates fingers might be avoidable...
Honestly, removing the trigger guard is better with a Blue Gun used in disarms training. If you're indexed along the side and someone wrenches the gun, your finger is already extended, they only need to wrench it outward and you've got a dislocated finger. It results in more injuries, not less.
This is also one of the reasons why the knife grips we teach are basically closed fists (no 'thumb capping' or thumb on spine) and why your BJJ instructor tells you to not put your thumbs on the inside of your Gi grips. In all those cases, any pre-existing extension of the digit makes for both a weaker grip and a grip that is easier to result in a jammed or broken finger through twisting/wrenching.
Also, ECQC uses SIMs in the EVOs. So you're trying to shoot the guy trying to take your gun.