I owned a KG-9 if any of you recall those things. Mine was semiautomatic, sorta
It was a small 9mm handgun that looked like a submachinegun and it fired from an open bolt using straight blow-back as a method of function.
The bolt was heavy in order to slow down the rate of fire in the full auto versions and this bolt was the same. You have to pull the bolt to the rear where it locks back and is waiting for you to pull the trigger to make it fire. the problem is when you pull the trigger that big heavy bolt is slammed forward and before it can actually shoot it has already thrown your aim way off target.
I also fired a Mac-10 in .45 in semi-auto mode trying to hit a brick. I learned that if I aimed high enough over the brick the bolt movement would put the round on target. It took about 8 shots to get that one down but with practice I might could have gotten good at it.