I think Hathcock said he carried 80 rounds or so.
Seems reasonable to me.
I agree with you that they don't need to overdo it, I've humped heavy stuff and wouldn't carry anything unnecessary, but, if memory serves, Zane had FIVE rounds, I haven't seen it in a while, can't recall how many they fired together.
There is a distinct possibility that a sniper will not get away after firing that one shot.
Most gunfights involve less than 5 rounds, but I load to capacity and often cary an extra mag.
Happy medium would be something more than a single digit round count, I think.
BTW, speaking of humping heavy shuff, anyone else notice that Zane's rig had no sling?? Could they not figure out the HK 3 point, or what.