When I first started composting water waste I tried spreading Hesstons and mini-Hesstons with a 10 ton Ktwo rear discharge muckspreader. Putting bales in whole just broke shearbolts, no matter how slow the trace was: it would snatch wads off the bale and jam up. I did a lot better by breaking the bales up a bit with the grapple before I dropped the straw in, but the throw wasn't very great. The straw was lovely and fluffy, but I found the only way was to leave the spreader stationary and scoop it away from the back with the fork and grapple.
Years ago I used to put boardy round bales of straw (we all bale a bit damp sometimes!) into a Howard rotaspreader, and it made a lovely job of spreading it. Knocked hell out of the spreader, and took an age to start, but a good throw of loose straw!