I am Director of R&D at AAC.
True.
300 BLK was designed as supersonic and subsonic. I see it as mostly a supersonic platform - the most reliable and powerful way to shoot 30 caliber from an AR15 that uses normal magazines at full capacity. Here is more info:
http://www.300aacblackout.com/resources/300-BLK.pdf I know about the caliber, thank you for the link. The information obtained when it was developed is what made me invest in the first run of AAC uppers. I would avoid 9mm cans for the reason stated - that it will heat up too fast. Stick with 308 cans that are FA-rated. There is no issue with primers though, so you either have bad ammo or you should have the chamber checked.
There is an issue with primers. Either we have a bad run of Remington Ammo, the uppers are not assembled properly, or the cans are at fault. And Im talking 12k rounds and 3 uppers, 3 suppressors. Pistol length gas on 300 BLK is much like mid-length gas on 5.56mm. This is easy to see just by noting that they both have gas ports of the same size on 16 inch barrels. 300 BLK is not less reliable on a 9 inch barrel with no can. And it is not more likely to blow a primer with the can on. If you do a QuickLoad simulation, you can see that peak chamber pressure occurs with less than one inch of bullet travel.
We do not warn of this in the user manual, and have not seen it in testing. Your blown primers were most likely the result of over-pressure ammo or an undersized chamber.
Must have been a combination because I don't see how 3 separate uppers with 3 of the same cans are functioning the same way. When I called into AAC for advise I was told to "not run the supersonic ammo thru the 9" uppers because they can over pressurize due to the short barrel and pistol length gas system". Guess I shouldn't take them for their word when it occurs every time we run supersonic ammo? The 3 of us ordered the suppressors from the same retailer at the exact time. They were the same run. The suppressors are not consecutive serial numbers so I'm lost on that one as it would be really hard to screw up 3 cans and they end up all in the same state let alone the same SOT dealer. Or it could be my ammo, like I said I only have time with factory ammo. Rolling my own never interested me due to having so much factory ammo available at the time it was conceived. There are no issues with AAC 9 inch uppers and 762-N6 cans. There is no disclaimer. And there is I have never heard of a blown primer that was related to a short barrel with a pistol-length gas and a can either in internal testing or any mention on the internet until you made these posts.
Pretty bold statement when there are clearly some issues with the uppers and the cans have their own issues entirely. Might want to read around on the multiple users complaining of poor fitment to your mounts.....
Your sales staff made the disclaimer on the phone while I was trouble shooting the SBR, as well as my two friends that own the same setups.
There is a first time for everything! 
