"M590A2" shotgun?

[Slater]

http://safety.korea.army.mil/Toolbox...FMAN31-229.pdf

The above USAF manual mentions this nomenclature. Is just a USAF-peculiar designation for some M590A1 variant?

[DMR]

I'll try to check my referances when I get back from Bragg. As I recall the USMC has a variant of the 590 with 6+1 capacity, but with a 20" barrel that is called the 590A2 in their Tech manual.

[m24shooter]

I wonder if it is just a typo.
There is another AF pub that is for the "500A2." I wonder if it is as simple as that.
The only thing I've seen called the A2 is the 500A2 and then the 590A2 that I've never seen officially attributed to anything but instead something that was used to describe the DAO 590 model.