I've heard it's around 1200-1300 # or about 1/3 cubic yard (not necessarily equal). I've a 410 loader on my 4010. It'll carry it completely full of gravel. The trick is to learn to curl the bucket and all to get it full when you push into a pile.
You'll need AT LEAST 300-400 # of ballast on the 3 ph if you're filling the 410 bucket full of gravel. Wouldn't hurt to have even more. It'll be really well balanced if you put about 500-600#(or more) of gravel in a box on a carryall on the back.
I seem to remember about 900 or so lbs. from the manual...and I use a ballest box that weighs at least 600-700 lbs.
As Ralph said, picking up heaping buckets (54" in my case) of rock or gravel is no problem for this machine.