The same as other HP rifles, must be safe, cannot be electronic or a "release" trigger. Other than that as long as you can close the bolt most of the time w/o it going off you're fine.
Joking aside, slam fires have happened from time to time. Once in a match and nobody is going to get upset, the second time I think you're going to start getting some attention. One of the better known F-Open shooters had one at Camp Perry, and it came up a 10, some people just can't miss. I once got in to a fast rhythm and I let my finger hit the trigger once as I closed he bolt. I got a 5 or a 6, which was 5 or 6 points better than it could have been.