Hello all

I am new here and new to the ar platform as far as building is concerned. I own one rifle and one pistol but this is my first custom build. So here is what I got
AAC 9" 1:7 twist 300 blackout upper with a KA hand guard
Dpms lower
And a bunch of other stuff. Mostly magpul extras on it.
My question is how long should the buffer tube be. I am trying to make it short but right now it sits at 25" long. Can I use a shorter buffer tube?  I really don't know the science behind tube length. I do plan on getting a suppressor for it eventually as it already has the AAC qd flash hider. Thanks in advance for your help

I assume you mean that is OAL of the firearm and not buffer tube length!

At any rate, except for some bizarre ultra shorty configs that never really worked reliably,   the shortest "pistol buffer tube" is about the same as a carbine tube, ~ 7.25" overall length, before it's threaded into receiver.

- OS

So how are some ar pistols very short???

There's a few proprietary PDW bolt/buffer/extension tube set ups out there.

A standard carbine or pistol tube offers the most tuning options.

Gun Smoke Enterprises pistol buffer. Theirs is touted as "the shortest" at 4". For $295 it only saves you 3".
http://gunsmokeenterprises.net/product.sc;jsessionid=36589D644CC88DE475896A9812AD199A.m1plqscsfapp05?productId=5&categoryId=1
Also there are/is at least one company that does not require a buffer tube (Olympic Arms). Recoil spring is on top, I think.
http://www.olyarms.com/shop/pistols/ar-15-pistols/oa-93.html

Certain piston designs don't need receiver extension at all, not even sure it's quite fair to call them "ARs", though.

- OS