HSR or Host State Rewind calculates the position on your client, where you took the shot, and then its trajectory and then off the information from the other game clients calculates the enemy mech positions and figures whether you actually hit them based on their game position. In other words when you see and shoot a mech at a particular instance on your client, the other players mech may actually be at a slightly different position due to the fact you both have different information transfer rates between the clients and the host server.
This is where the 'phantom' damage comes from, you get no impact but suddenly show damage to an area of your mech.
The HSR combined with from what I have noticed with Hit Detection and some wonky hit boxes, lends to situations where you fire at a stationary target and do no damage. I have noticed solid torso hits not doing damage, and it tends to actually be a hit on a seam line between hitboxes. Especially with single hit weapons such as AC's/PPC's. It sometimes seems to be that you hit a seam and the server doesnt know whether to spread the damage between the two hit boxes, randomly assign it to one or the other box or apply none to either.
All these factors combined together can cause situations where your target appears to take little damage despite yourself seeing weapons impact.
Edited by ManaValkyrie, 23 October 2013 - 10:42 AM.