My 403's have stretched so much that I can now wear my orthotic insoles (which are a little bulky) in my 403's. When I first bought the boot in the summer I could not put them in.
Are they loose, yes.
I wear a size 10.5D and tried on a 10D when I was looking. The 10's were very tight to the point of uncomfortable.
The leather has since stretched and softened making them all that more roomier, which makes for a sloppy fit.
Maybe I should have stuck it out with the 10's if I knew the leather would have stretched that much.