You can never go wrong with LMT. MARS-L is an nice rifle, and the barrel swap is an added benefit. I might have one with your name on it, when you are ready.
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When a guy has narrowed his research to 2 or 3 rifles, the last thing I want to do is open the door for you to consider others. I like to keep the selection to a max of three. I have no experience with ADM. I am assuming this is the same company that makes the rifle mounts?
The only comment I would make is that you have chosen 16" and also said "long range." I would probably guide you to a longer barrel for long range. Most of the 16" rifles will be carbine gas, and I would prefer a mid-length gas system for smoother shooting, or even rifle length. But, long-range is subjective with an AR15 style rifle anyway. LMT will offer the ability to upgrade to SS barrel. Pretty sure that chrome-lined is their standard, which is not known for the best accuracy, but is more of a military grade for durability and corrosion resistance.
You did not mention the optic, but in the 1-10x, we are sure a fan of the Razor Gen III. A little expensive, but hard to beat with true 1x magnification. I do not mean to be overly commercial, but we do offer a nice combo deal with optic and rifle and for 'hide guys as well. But, happy to help you if you just want to chat.