The way I have gotten around COAL's that are longer than the mag box is to just put one round down. The top round in the well is above the mag box wall. Basically a two shot repeater. that being said, I have never benefited from a third or fourth shot on a big game animal and I have only benefitted once by a second shot. That was while antelope hunting
and i got one with the first shot and dropped the second on the run with the second shot. All my kills have been one shot kills and all my misses have been complete misses and anytime I tried rapid follow up shots, they were misses also.
If your bullet shoots just as well with a COAL that fits the Mag, then use it. My priority is accuracy and I'll take the two shot solution if it means better accuracy.