Looked through the SBR FAQ thread, but it's focus is on more of the legal issues. All good stuff, but didn't see these two questions:


1. What are the pros and cons of a, say, 10" SBR AR-15 as compared to a more standard 16" AR-15?

My understanding is:

Pros
+ Shorter (obviously), and thus more maneuverable in CQC
+ Lighter weight

Cons:
- Louder and/or more concussive

What else?


2. Is 5.56 really a good caliber for an SBR? Seems like a lot of energy is lost and not transferred to the bullet (and instead transferred to the shooter as a concussive smack). How do the physics of this work? Is a heavier caliber fundamentally a "better" choice for a gun with a 10" barrel?

Not really.  In something like a 10.5" barrel, a tremendous amount of energy just goes into making a lot of muzzle blast and flash.

I don't know about that....somehow, most of my SBRs suffer from a severe case of bloat.



"Good" for what? Killing things at 300m? Yeah, something else would do a better job.
Having lots of fun at the range? It does a great job.

SBR’s are louder but I unusually shot with ear-pro (and/or suppressor) on so it is not that big of a difference over 16”.  Also, I’m usually not shooting over 300m with a 5.56.  The shorter barrels come in handy when you put a suppressor on the end.  16 – 20” plus a suppressor = LONG.

The 6.8 SPC performs well in an SBR.  I like this caliber when I want critters dead.  However, it does not see as much range time due to the expense of the ammo.

How quiet can you get a 10" AR with a suppressor? Roughly as quiet as a 16" AR?

And I've heard that suppressors wear out faster on a rifle with a shorter barrel. What kind of life would one expect from a 10" AR vs. a 16" AR?

The 10” or more commonly 10.5” will be louder than the 16”.  Several suppressor companies only warranty barrels 10.5” or longer.  I personally like the 11.5”.  It gives a little bit more protection for the baffles and also gives a little more FPS to the rounds (12.5” is my favorite in 6.8).

I’m not sure about life span as I have not worn one out yet (only started into the NFA world a few years ago).  There are a lot of variables in play: type of metal in the can, ammo, breaks vs FH, firing schedule, etc.  

I put a lot of time worrying about life span when I was first searching for a multiple purpose can for my .308’s and 5.56.  I finally came to the realization that by the time I wear it out, suppressors are going to be so much better, that it will be time for another one anyway.  Suppressor technology seems to be changing pretty fast right now.

a SBR in 5.56 is perfect, if you get and use 70gr TSX barnes bullets they should reliably expand out to 150yrds since they expand down to 1800FPS

i have not shot my 16" ARs since i built my SBR.. and i cannot imagine shooting the 16" again unless my SBR breaks or something.