I wouldn't shoot that.  

It would be easy enough to get a different type of muzzle device and do it the right way.  As is, I would have concerns about everything lining up.

What's the white stuff in your passenger floorboard?

It lines up pretty decent right now. I'll get some better pics when I get off work, it feels sturdy too.

 

You don't want a plastic frag grenade in front of you.

That brake is going to blow the handguard plastic apart, maybe on the first shot.  

Plus only threading a muzzle device on 1/4 of the way is asking for trouble.

This.

A brake can do this to a metal rail: (actually, it looks like a BCM Comp from the end view)




http://www.ar15.com/forums/t_3_121/622312__ARCHIVED_THREAD____300_build_question___.html&page=1#i6160589
Unless you want plastic hands like Chuckie from SoA, don't even think about shooting that upper until you buy new handguards.



Also, with the threads only engaged 1/4 of the way & no provenance about the spacer I would say there is at least a relevant chance that:

A) The brake may be misaligned with the bore enough to cause a bullet strike, which would be very bad

B) Who made the barrel? Too little thread engagement could actually cause the pressure wave to strip the barrel threads and chuck the break downrange.
 

I wouldn't shoot that.

A Noveske KX3 Pig would work and look good. IMHO


...and I wouldn't shoot it as is either!!