[Travis McGee]

Because caseless rounds have a severe problem with removing heat. Cased rounds dump most of the heat into the shell, which is promptly physically ejected. Caseless rounds dump that heat into the chamber, where it disperses slowly. While you can fire mag after mag for hundreds of rounds from a regular design, a caseless system will overheat way too early. H&K had such a design long ago, but they never resolved the heat problem.

If I recall the history correctly, they then had what is called a "cook off" problem. Troops really don't like this problem.

[ctdonath2]

Consequence of what I described: there's too much heat in the chamber that cannot be physically & rapidly removed ... ergo, after several rapid shots it's really hot in there, enough so that the next chambered round, if left to sit long enough, just plumb goes off.