Strike industries pistol buffer tube kit - Strike Industries AR-15 Pistol Buffer Tube Kit

This is the best way to go for that short length you are looking for in a pistol build.
The short buffer is strange looking, but works like a charm with several different types of ammo I used.
Just the ticket for a pistol build you may be doing and not real interested in a brace, but I'm sure you could put one on this if you liked.