In the factory stock, with AR magazines, my Ruger fed just fine. If you’ll look closely, Ruger positioned the AR magazine well-forward and closer to the chamber in 223, 300BO, Grendel, 350...as well as the Mini 30 mag based 7.62x39 American Ranch. Less distance traveled...
Much the same as the guys setting up shorter cartridges like 6mmBR in magazine fed bolt actions...short cartridges in a regular sized short action cause inconsistencies in feeding. The shorter overall length of the Grendel cartridge running in a Magpul stock (much improved over the factory stock) with AICS magazines induces a very long travel distance for each round feeding from magazine to chamber. Thus, you’ll find fiddly-ness in tweaking magazines to properly and reliably feed. Ruger American short actions are “one size fits all”. Micro sized actions, being shortened vs standard, do not require stubby cartridges to travel nearly as far...
To be sure, it’s all self-induced, solely due to the desire for a better stock. If Magpul offered AR magazine bottom metal for their stocks, I would try it out in a heartbeat. A man with a higher than table top quality 3D printer could feasibly print up such a part.