Hi guys I recently finished my first build which was just a 16" 556/223. And now picked up two lowers PSA had on sale for $49. My wife wants one for herself and she wants it white and black so hers will probably be another 16 or 18". But for mine I am going to start a pistol. Was looking for input on different lengths between 7" and 10.5". I've read some about some running better than others.  I was thinking maybe an 8.5". Anything I should know before I start the build about it? I know the laws and what not as far as no stock and all that, that's not what I'm looking for. Just any heads up for a pistol build? Is a .750 gas block/ tube right for it or does it need to be smaller? I like the look of the hand guard going all the way to a flash can so will probably go with something like that.

Everybody has preferences, but you can essentially do whatever you want.  Should be no problem with the barrel length range you've stated.

I have both a 10.5" and an 8.5".  I love the 10.5".  The length feels good to me.  The 8.5" runs fine although it does eject the brass at about 2:00 position.  A bit bigger fire ball on the 8.5".  I run a KAK slim Flash can on the 10.5" with a 10" BCM rail.  The 8.5" has a short fat KAK flash can.  Both are very accurate for me.

IMO If you're building a 5.56 I would stick to the 10.5-11.5" barrel length for velocity purposes. If you build a .300 BO then I would venture into the shorter barrels. An adjustable gas block is always nice in case you need to tune it back some as most seem to think gas ports are slightly oversized these days. The size of gas block you use will depend on the requirement of the barrel you choose. I was going to use a KAK can at first also but ended up going a different direction since the can only redirects the blast and doesn't have any other qualities.

Yeah I think you're going to find most pistol barrels have a .75 shoulder for gas blocks, not many pencil barrels for pistols. I have a 5.56 rifle, but chose 300BLK for a pistol so I could stay a little shorter 9.5" and get full burn. I really like mine, im also building a 22lr upper for it for plinking.

Thanks for the input guys. I thought about a 300 blackout but only reason I was leaning towards a 556 was bc I already have a rifle chambered in that. Just don't know if I'd regret not doing a 300.

The biggest consideration with .300 blackout is the price of ammunition but if you shop around and watch sales you can find it for reasonable prices.

I built a 7.5" 5.56 with an SLR adjustable gas block, standard buffer and I have had zero issues with it.

Thanks for the info. Jason I was actually looking at your 10" barrel. Planning for 300 aac and was thinking about 10" for if I decide to do some hog hunting or something with it what can an 8.5" usually poke out to and be fairly acccurate.

This has a 7.5" stainless barrel, 1X7 with .223 Wylde chambering, came with the pistol kit from Thunder Tactical.  KAK Micro flash can and the 7" hand guard comes within about 1/8" of the can portion.  Function is outstanding and very accurate, although I have only done shooting at about 15-20 yards with a cheek weld, no other support, with the flip up Magpul sights.  The barrel profile is basically the same as an M4 barrel, without the undercut on the forward portion (obviously).  I did not find any disadvantages to the 7.5" barrel and would recommend it if you are wanting to stay short.  Even with the rough and creepy milspec type trigger/hammer I was able to keep many of the holes on the target touching or creating one big hole.  I was rather surprised how accurate this thing could be even with such a short barrel and the recoil was not bad at all.  

I built what I call my "Frankenstein" pistol out of spare parts. It has a Diamondback 7.5 upper, PSA BCG and MOE LPK and MagPul flip up sights. I bought a KAK Shockwave kit. It feels perfect. It is short and just short enough. I have not had a chance to fire it yet. I hope to soon. It does have a standard A2 flash hider on it. I want to get one of the KAK brand muzzle devices at some point.

I hope to have some pictures uploaded soon.

Enjoy your build and keep us posted.