Here’s a good thread on the safety issues with blanks - they can still be deadly:
p.s. They add the muzzle flashes in post now anyway, and they can even cycle the slide and add a shell ejection in VFX. Having live blanks on your set is not worth it. No show or shot is worth risking people’s lives.
But because this prop gun had a plugged barrel, that means all the blast — 1/2 the gunpowder required to propel a bullet beyond the speed of sound — comes out the SIDE of the gun.
And because these are, in many cases, real guns firing blank round with 1/2 or 1/4 load, they tend to jam and misfire. Which means you frequently wind up with an actor or prop master frantically trying to unjam the thing so you can keep shooting. Not a recipe for a safe set.