so due to the ability of the exp sniper rifle the bullets go fully through every thing and the explosive never get placed by the expermental 50c bullets making it just a normal bullet but much more expensive
The impact-detonation is not a guaranteed thing, there is a chance they explode on impact, but its more likely they dont.
But if you shoot and dont hit a enemy, then that projectile will become a mine, and from what ive gathered, that will happen every time.
Have a look at the ammunition description, if my memory is correct the description clearly states the above mentioned behaviours.