There was only one guy on Biggerhammer that use to post about his, he never had any problems with it. He ended up selling it and buying a different .50. Another guy posts on AR15.com in their .50 forum that owns one but I'm not sure if he's even shot his. I think the archives on BH got zapped last year during a server change. As much as I hate to say this, do a search on a guy that posts as "Ricka". He's (stolen) put alot of info on his page from BH, he has a link on most of his posts. He might have some of the old Hesse/Vulcan stuff saved.
Here's the strange part about Hesse/Vulcan, they changed the bolt design on the newer ones to interupted threads. Can't figure out why they would use a design like that knowing the pressures involved with .50 BMG. If you really want one, see if you can find an older one with the original bolt design.
Haven't ever heard of one blowing up, just failure to fire, bolt handles breaking off. These are not unusual in the .50 world as some surplus ammo has hard primers and people do (myself included) use a mallet to open their bolts. I did read a thread on another board where a guy claims that a guy lost a thumb and almost an eye when one let go.