The carts were intended to be shot from. Think it was a great idea on paper ,but for all practical purposes it was just a good way to transport them around over fairly smooth surfaces ,and for training.
In most of the watercool related books there is mention of makeing a "T" base out of wood ,sticking the 1917 tripod on it ,and putting sandbags on all 3 legs to hold the tripod down. I believe the M1 machine gun mount (cart) was developed out of this idea around 1930. Here is a quote from "Machine Gunners Manual 1936".
M1 cart
"When taking posts, the members of the squad have equipment as for advanced gun drill, except that No. 4 has the aiming stakes, the spare parts roll and two boxes of amumunition and No. 5 has a T-base, a shovel and three sandbags.
Infantry units equiped with the new type cart (M1) embodying the steel T-base, may use it in place of a wooden improvised T-base. When steel T-base is used in battery drill, it is optional with the instructor whether the tripod and gun be removed from the T-base, or the assembled T-base, tripod, and gun, be handled as a unit."
There are some pretty good line drawings of the wood model of 1917 cart ,but the are no dimensions.
Here is a description of the M3A4 series
Thanks for the compliments. Its alot of work, scanning, uploading (Thanks you highspeed internet) Most of the black and white pictures of handcarts are from real photos I own or from books I own.
Craig