OK I took the time to look, its a *.ukx file for UT2003 anyway, I assume its the same for 2k4. The sequences for the assualt rifle are as follows:
Idle - animation played when runing around etc., ie not firing, moves slightly in time with breathing etc,.
rest - As far as I understand its there to break up the idle animation - if you're idle for a certain amount of time it plays this just to add a bit of interest.
select - animation played when you select the weapon, i.e. usually bringing the gun up into view, instead of it just appearing
putdown- the opposite of select - holstering the weapon if you like
fire - hmm now what could that be?
fireend - animation played at the end of fire, if its a constant repeating weapon (like the pulse rifle) it plays once you release the mouse button, not each time it actually fires
altfire - obviously the animation played when you altfire the gun.
Hope this helps, obviously some guns have extra animations - for example the rocket launcher has a 'load' animation where it loads a rocket into the chamber for when you load 3 up etc. If you need any more info then ask and I will do my best to help