I'm building a .600 on a custom falling block(not a ruger-it's a design of my own roughly based on the Ballard, only very, very, much more beefy), but have not ordered the barrel yet, so it may turn out to be a .577, if from what I hear on this thread is serious enough to change my mind.
I've shot .577's before, and they are great-not at all hard to recover for follow-ups, in fact, not bad at all. Of course I realize I'm a smaller man compared to most, and I deal with recoil differently than men of large stature. This makes a huge difference. The .577 kicks, yes, but to me, it's not something to be at all concerned about, even in a single-shot heavy barrel.
But, having not fired a .600 before, I'm having an itchy feeling about the .600
Plus, the .577 has cheaper and more readily available loading components, especially with jamison brass.
But oh well, there is something of a mystique about the .600 that I would like for my personal needs. It's weird.
When I get some photo's taken of my falling blocks I'll post them.