I think he shot 7 times. 4 in the first conflict against Rosenbaum, which might have been over a struggle for the gun and he actually might not have killed him (the 3rd shooter might have killed him). Then one round that was where a guy kicking him would have been if he continued the attack.  1 into the chest of skaterboi. 1 to disarm Gaige. Rosenbaums wounds included shots to his hand, head, thigh, back (lung and liver hit) and pelvis.  It's very likely the back shot was not kyle and that seriously calls into question that Kyle killed him.