T2--
I was concerned about the shell holder type also before I bought my State Arms.
I talked to several of the guys on the Barrett Board, and the general consensus was that the State Arms gun WILL NOT accidentally discharge, even if you drop a "loaded" bolt. It is built extremely well. I have yet to fire mine, but I have tried several ways to make the gun "fire" with no round in the chamber/holder. This includes dropping it onto a carpeted floor (not brave enough to ding it up on anything solid), holding the trigger back while I insert the bolt, inserting the bolt part way, etc. And I could not get mine to "fire".
One of the guys on the board who is familiar with these things pointed out to me that the military standard single shot .50 for years was the AMAC, which is also a shell holder design and they did not have trouble with mis-fires.
I am not sure which gun has the reputation for problems (maybe the Grizzly?), but it just takes a little care and you won't have any problems. I also learned that with single shot guns, you don't load until you are ready to shoot anyway--if you look at benchrest guns with triggerpulls in the Oz. rather than Lb. range (closest things to .50's), they are always set up on target before they are loaded.
AFARR