Complex sentence: A tactical limitation of the GSh-6-23 is that its rate of fire is such that maximum burst length is extremely limited; the MiG-31, with only 260 rounds of ammunition, would exhaust its entire magazine in less than three seconds.
Split into simpler sentences: A tactical limitation of the GSh-6-23's rate of fire is that maximum burst length is extremely limited. The MiG-31, for example, with only 260 rounds of ammunition, would exhaust its entire magazine in less than three seconds.