Anything with a detachable magazine is capable of accepting magazines of more than 10 rounds. In general, a detachable magazine is a tube, a spring, a bottom to the tube, and a follower on top of the spring. For guns that accept detachable mags, you can just make the tube and spring longer, and you've got more capacity. There nothing inherent about the
gun that does (or really can) limit this.
I mean, 1911's in 45ACP are generally thought of as taking 7- or 8-round magazines. But:
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All of this just illustrates why having people that do not understand guns draft gun regulations is profoundly stupid!