In an effort to focus on different areas of the AR pistol...

9mm AR pistol buffer assemblies

Well, here's my 2 cents worth. The model 1 sales pistol buffer (short) which utilizes the 1911 long spring sucks ass.

I resorted to using the buffer tube from a Bushy short entry stock which functions flawlessly.

The "original" M1S pistol buffer assembly will NOT work w/ a 9mm upper (or any other pistol cal upper w/ a solid back carrier).  The incert that the M1S buffer has no where to go on the solid backed (aka weighted) carriers.  Also, the guide rod goes IN TO the carrier, again, solid (weighted) carriers have no hole.

Someone modified a M1S system by taking a normal CAR buffer and cutting it to fit.  Granted, I assume that the bolt hold open would not work.

In order to have a buffer assembly that will work w/ 223 and pistol cal, it seems the 'only' choice would be the ACE system or the 2nd gen M1S or similar styles.