I hear what you’re saying but i dont like the idea of loading through the ejection port…but there are (this is only my thoughts not facts) 2 ways of going about making an ar that has an internal magazine which could still be recharged without taking out the rear take-down pin…my first thought would be something similar to an enbloc (from an m1 garand) that would be fed through the ejection port, and my 2nd idea would be a purpose built upper with a similar design to a belt fed gun with a section that can be unlatched and swing up and allow access to the mag that is locked in place and a stripper clip or a mag lula could then be used to recharge the magazine…either way would be a lot of money and time in R&D and with a somewhat limited market…glad i could contribute to the novel though.
the reason i say i don’t like the idea of loading through the ejection port is if you were to accidentally hit the bolt release while your finger(s) where in the upper, it would fuck your day up in a jiffy.