I forgot to say but we were always pretty fastidious about machine gun barrels used for what we call 'overhad fire' or 'battle innoculation shooting' where you fire over the heads of advancing troops during training or suchlike. Then it was always a 'what the calibrated gauge says' attitude. I just get the feeling that the troops would feel somewhat peeved to find .303 and 7.62mm machine gun bullets dropping short in amongst them when they were out there. Even worse, just think what they'd say if a stray bullet knocked a hole in his tea mug! No tea! That'd get him pretty angry