"You may not believe this, but even a good towed arty crew, if they have the prepared ammo on deck, can kick out 12-15 RPM."
Maybe 15 RPM on a 105mm with a good gunner. It gets unsafe beyond that, IMHO.
"Back when we practiced Zone and Sweep missions with HE, each gun had to fire lots of ammo in a short time to get good effect on a large target."
That's a LOT of training ammunition. I assume those were the last missions shot on LFXs?
"Can do it if you use ramming staffs instead of the rammer on the M109s"
Elbows and a-holes everywhere. It can look like a Chinese fire-drill.
