I'm currently playing through the H2 legendary playlist and was just wondering, in the mission Metropolis when you've just left the tunnel, how many Jackal snipers are there? It took 1 and a half Beam rifles to kill them all as well as as few attempts. I'm pretty sure they actually respawn on that part of the mission if you don't progress through the mission fast enough after killing them.
I can confirm this statement. In the same area as discussed I utilized the warthog that was driving around and only had to kill about 4 or 5 snipers. However, I HIGHLY recomend using the warthog. The next area over has a couple of ghosts and wraiths that you can more quickly kill if you utilize the warthog. Not only that but it has a high rate of fire and no ammo limits, so using it is much easier compared to sniping especially if you didn't activate the infinite ammo skull (me). At least that's how it worked for me, others find different methods as well, so finding which one works for you best will take some trial and error.