I doupt those guys are from PLA, the camoflage just doesen't seem right...I'm quessing these guys being Taiwanese...
How heavy is that round? I suppose it should 50kg more or less.
normal 155mm round weights 45 kg. So carrying them around is quit bitch thing for long periods...
Those helmets really are not the ideal for the artillery. It should be wide enough to have the earmuffs being properly wearn. In-build earblugs doesen't work becouse you never can get them tight enough. In overall you need these little earblugs stuffed in your hearing canal and atop that earmuffs, thats the only way of protecting your ears from hearing damage.
The dude without the helmet is most likely either the gunleader or aimer as those two needs earmuffs which can be linked to radio. I'm quessing these guys have to swap the muffs everytime when talking to radio, so a helmet would be just a drag...