[Zoe's Echo]

Mathmatical answer still 50% the result shouldn't change the original probability.

Non-mathmatical answer - I am not clear as to as if it was a rotation firing - marksman first than Hornblower or simultaneous.

If it was a staggered firing and Hornblower had the second shot after the marksman then the odds are 100% since if the Marksman fired first and came up without a bullet there is no doubt I would've fired back.

If they fired at the same time still 50%, Hornblower might never have fired because his chances of hitting the marksman were so small he might have assumed that his only chances to survive were to have the bullet or get missed.

Good Luck!