Can this be improved on my client?
IE can I do something with my computer, firewall, applications, Operating System etc?
Or do I just have to find a faster connection?
There's nothing you can do at all except move closer, same thing i told kaos. The 400 millisecond time is how long it takes for you to reach a US based server and back again. A faster connection can't help you. The term "faster" when used in this way is actually a misnomer, which most people don't realize. Think of it like this: a higher bandwidth connection is like increasing the lanes on a highway. It allows more cars through, but you doesn't mean you travel at a faster velocity (just pretend traffic jams don't exist). All internet connections travel at the speed of light through fiber trans-ocean cable. That speed can not be improved.
I assume you mean latency?
How much does latency affect game play? I am getting really frustrated at the inability to snipe, particularly when the LGM looks like it should be dead to me - e.g. Pill lights up at the SAME time as the LGM is inside. Yet I watch a log and see someone run in and make a successful snipe when I know that I do the same thing in a game, even earlier, and my snipe is unsuccessful.
I will give you another example. I shoot a tank at sea from fairly close, I hear the sound of metal on metal, but the tank survives. What I interpret from this is that my client receives the hit message before the network message is able to go to and from the server. By that time, the other tank has moved out of range and the server message is that the tank was missed.
Another example is dogfighting. I ran in on Azz in an open from the trees after he had taken a pill using a block. He did the take quickly and therefore he took quite a few hits. I had full armour and started blasting him and he started blasting me. By the time he died I was about two shots from death. He should have died way before that IMO - ie there is no way he only took two shots from that pill. BTW I can never win a dogfight unless I have full armour and the other player has been hammered in a previous stoush.
Similarly when a game dies in the arse. The pills can be shot and they can shoot back but they don't get angry because that message is no longer arriving from the server.
So back to my question, is the latency of my network connection a significant hindrance on my ability to play, ignoring the issue of hand eye coordination.