The Course of Fire for NRA Mid Range Tactical Rifle (AR) does NOT indicate the type of fire (i.e. "slow" or "rapid"), only the distance and target to be used (Rule 7.20). This is where the whole problem resides, IMO. My understanding is that in this classification, matches are usually fired together with Conventional and/or F-Class shooters, and are typically prone slow-fire events. If so, the rules clearly state that only one round can be loaded at a time (Rule 10.1.6). However, that would change if a Mid Range Tactical Rifle (AR) was used during a rapid-fire course of fire, which, as far as I can tell, should be perfectly legal. I assume that that is the reason that slow vs rapid is not strictly specified, because both are possible options. So technically, it is the course of fire (slow vs rapid) that should dictate whether rounds are actually loaded one at a time, or more than one. Even then, the Slow Fire rule only states that "The cartridge shall be inserted in the magazine or chamber", it does not specify that you MUST feed from the mag. From this, I'd interpret Rule 3.3.3g that a magazine "must be used" to mean that a mag must be inserted in the mag-well, nothing more.
On the surface of things, that would seem straightforward enough, and is the format currently used with other High Power disciplines. However, it still leaves the other ammunition issues unaddressed (i.e. Mag-length only?, Commercial versus handloads?). My gut feeling is that they didn't specifically address these issues because it is almost impossible to do so in any coherent manner given the minimal caliber restrictions. Mag-length doesn't mean much when a variety of different calibers with loaded rounds of dramatically different lengths (and/or bullet lengths) can be used.
Unfortunately, that also leaves the question wide open IMO for those wishing to game the system and use long handloads with high BC bullets. There is nothing in the rules that specifically states that to be illegal, even though it clearly seems to be in violation of the intended spirit of the competition. For that reason, I can imagine that some Match Directors might not have a problem with long handloads, whereas others clearly do. Therefore, having the rules interpreted in different manners at different shooting venues is potentially a very big problem. Given that much of the intent of this classification seems to be the theme of "inclusion", perhaps the rules were specifically written in such a nebulous manner. Nonetheless, I think it will be important to rectify this rather fuzzy area in the rules as the sport grows, such that they are uniform AND uniformly-applied at different shooting venues.