Hi SStomcat,
Our club does a big bore shoot every month and there are usually around 15 shooters. Two, or occasionally three of us shoot doubles on the course, the rest shoot bolt guns. Calibres spread from 375 to 505 for the bolts, but mostly 375. The doubles are 450/400, 450 No2, 470 and 500.
Without exception, every time at least two of the bolts have problems, usually feeding problems, or exection problems or short stroking in the heat of the moment. The doubles have a very occasional issue, but seem to be far more reliable than the bolts.
I am just stating what I observe. Some have said that the Zim guys don't maintain their bolt guns well, and that is the reason. But then I can assure you they maintain their doubles even less because they don't know what is in that black box.