Rounds per minute is cyclic rate. Its never intended to convey sustained fire.
For example an M61 Vulcan cannon has a cyclic rate of 6000 round per minute, but the magazine is limited to 400-500 rounds. So it can fire a few 100 round bursts.
Sorry, my bad. I actually had two questions that I combined into one very bad question. The first question should have been would they actually test the cannon to determine what would happen to it if they, indeed, tried to fire 200 or 300 rounds through it and what is the limiting rate of fire on the cannon. Second question, is what is the practical limit on the rate of fire? If you are shooting multiple rounds at a target, how much does the rate of fire affect you when your cyclical rate is 200 or 300 rounds per minute? 300 rounds per minute sounds much better than 200 rounds per minute, but is it when you shoot two, reaim, shoot two, reaim...?