I'm looking at the 2013 AAC thread specsheet, specifically at the two 5.56 diagrams. On the first, it gives the spec for the special thread R. Silvers made to provide tighter fit with the Ranger 2. Interestingly, 0.563" is listed as the minimum shoulder diameter, though it doesn't seem clear to me that this is only for use with the Ranger 2.

The second 5.56 diagram seems only to represent a standard M4 barrel, mentioning nothing about minimum shoulder diameter.

My questions are:

• Does 0.563" represent an acceptable minimum shoulder for use with 1/2x28 threads for use with thread-on suppressors other than the Ranger 2?
• Does 0.563" represent an acceptable minimum shoulder for use with suppressor quick attach mounts that index on the shoulder?
  
  If not then
• What is the accepted minimum standard for 1/2x28 shoulder diameter for either or both?
• What, technically, occurs when too thin a shoulder is used? (Does a device "ride over" the shoulder when torqued down? Deform it?)

ADCO uses .560" as their bare minimum. Yes, a too-small shoulder provides insufficient surface for silencer mounting and can deform, ride over, etc.

Thanks, that's what I was looking for.

Yep, a .030" shoulder is pretty much bare minimum, some want at least .040".