Im wanting to do a scene where a bullet is seen coming from the barrel in slow-mo. can anyone tell me how to get the best blood splatter out of this?
Maybe you could use the fluid simulator to get a nice effect 
Depends on how realistic you want it. Blood will spatter under those conditions as a blob that will split it into droplets, which will stretch under force into an ovoid shape, much like an egg. If you’re going with very slow motion, you might start with a group of overlapped meta-balls, then let them separate outward in a ring. If you show the droplets hitting a surface, they’ll break appart into a spray of much smaller droplets, with a ragged, circular patch probably sticking to the surface. Blood is very viscous, so it will tend to stay in a spherical blob, even under high pressure.