IIRC, 95# for the 155mm HE round. The Marines use only towed 155 howitzers, the Army has a mix of towed and self-propelled (SP). The SP M109 has only power for ramming the shell, not picking it up, unless that's changed with some of the newer variants. Then, the difficulty depends on whether the loader is working out of the on-board racks or having to lift it from the tailgate when the shell is brought from the ammo vehicle. With the on-board racks, you work from about chest-high to belly-high on the ramming table.
In the video I watched, the shells were lined up (”pointy end” straight up...:) and the guy would walk over, bend down, pick the thing up cradling it, and crab-walk about 10-15 yards over to the weapon!
My back got sore just looking at it sitting in a chair, but...you know how 19 year old guys are.