So I'm looking to build two AR's and after a lot of reading, research, and pros/cons....now I would like opinions

One will be .223/5.56 and the other 300blk. I want to SBR both and think I will go with both a 10.3" Noveske or Rainer arms barrel. My question for ballistic purposes is 10.3 the shortest I can go for a quality tac driving? I will also suppress both, does this make a decision on length of barrel I select? As always thanks for your input.

Pete

I own a 10.3 in 5.56. It wasn't really built with accuracy in mind but works well out to 100 yards give or take, meaning I can hit a bunny pie size rock etc with no issues and I suck . I like the cool special agent orange look and if you run a can on it vehicle operations are a lot easier. My only dislikes are loss of velocity, stick with 14.5" if you care about that and I had to run a anti bounce H3 buffer and a wolf carbine spring to get it running on my RR. Bolt bounce may not be as much of an issue if it is semi only. But after tinkering around with it runs like a ape on M855.
   The 300 is actually up on my want to build list and if I was night hunting hogs and dogs with a can that's what I would want. But I've never had that much walk off after a 5.56 either. The ammo  price and availability even though that is starting to change are my only detractors.  Repost this on the NFA tech or SBR board. A lot of super helpful and knowledgeable guys are on them all the time. I still owe TonyK and JBnTX a big thank you for all time spent explaining the mechanics of this stuff to me. Hope this helps

10.3 is my barrel and shortest I will go for 5.56.  Not a tack-driver but certainly effective at 100-200.   Past that ....

Many manufacturers will not warranty their suppressors if they are used on a barrel much shorter than that.  I have a .300 Blackout pistol with a 9" AAC upper, it's very nice but I don't think I'd go any shorter than that for .300, and no shorter than 10.3" for 5.56.

If you want more answers and/or more reading to do, there is an AR pistol section under the AR-15 tab with lots of discussion on shorter barrels/uppers and also an SBR section under the Armory tab with even more discussions.  For 5.56, a lot of people like to tag along with the BCM decision to stick to 11.5" as the shortest barrels they use.  Pretty much every time someone asks about that write up gets linked.  

For me I got both.  Started with 7.5inch as when I think SBR, I wanted something that was actually shorter than my 16inch upper and substantially enough to make it worth going through the SBR experience.  I then wanted something a little longer along the 11.5inch range and ended up going with a 12inch PSA upper simply because the price for that complete upper during one of their sales couldn't be beat.  Unfortunately I haven't had time/energy to get out and truly site them both in and do some testing at 100yards.  Really wanting to get a SBR AR setup in 7.62x39, but need to get the two 5.56's 100% before that.  The E-file/paper file issue has one of my lowers on hold for now.

EDIT - as mentioned in the post above, check around with the manufacturers of whatever suppressors you are interested in as well since some won't warranty on shorter barrels.