Sniper bullets don't register as a hit/kill

I've tried several times now when sniping that my shots don't register as a hit/kill. I've been very cautious about holding breath and not move when firing upon a target. So there are as few variables that can affect the shot. Today I did all of the above and I'm 100% sure that I was on target, but I did not get the hit/kill. After I fired the shot, the opponent when to a prone position and I could locate the impact of the bullet on the wall exactly behind the opponent.

Ive experienced this also, today i had to hit a static target about 3 times before he got hit.

I was slowly targeting him as he was not moving.
Only the 3rd time i fired at him, git him but still did not kill him, (there was blood splatter then he ran away lol)
. This was with the m40a1 with long barrel.

It happens often. But i give it tge benefit of the doubt if i quick scope or theyvare running, but it happens to static targets when im prone also.

Hit reg needs lots of work

@naut I'm certain it is a hitreg issue. I've noticed that same problem in online play but during local play; all targets go down with one shot.