It all depends on the guy loading the rounds.. I am a small person, and I know I can empty the 13 round ready rack on a Leo C2 in quite a short time..you also have to take into account whether or not the gunner acheives a hit or has to apply corrections.. but I would go on about one round loaded every 5-7 seconds.. slowing down after a dozen or so...
Once I have a round up the spout, I hit the loaded button, and am reaching down for the next before the shot is off.. as the breach ejects the round, I move it out of the way with one hand then load the next round. Pretty quick process.. drop by the armour school sometime, and I‘ll gladly give you a shot at it..
Bzz