I've been bouncing various schedules of builds versus financials in my head for the past 7 months now.  The NFA way is neither the poor nor the dumb man's game.  So i jumped on this upper while at the the only gun shop out of the three in Key West.  It's a Sig Sauer and I trust them.  I've only had guns for about 5 months, which consists of a Sig c3 1911 and a wonderful custom built 223/556 AR15.  The AR consists of the quality names but i'm in love with Sig.  So The weekend warrior manning the counter knew his stuff but he seemed clueless about the last of a shipment of Sig .300 blackout upper assemblies.  He texted the boss about the price and came back with $350.  I went home as it was closing and did some light googling for keyword variations of 'Sig 300 blackout upper assembly pistol sbr m400'.  I couldn't find exactly what i'd seen but anything close was two to three times the price.  I went back and snagged it up before it was built into something hanging on their wall or lost to someone else.  I paid and he handed me the upper, fresh, clean, paperless.

I've spent a good 6 hours utilizing all of my research power short of getting back to the gun shop and talking to the owner with little more than more confusion on my docket.

Here's the skinny:
It's a Sig Sauer complete upper assembly
It's got a 9" barrel
quad rails
It says '300 black out 1:8' at the end of the barrel
An unmarked and unremarkable compensator
An unmarked charging handle

This throws me a hair:
It has an Umbrella Corporation Bolt Carrier..
..But the bolt is unmarked

I'm a numbers cruncher and a data geek and I want to know the specs, the part numbers, the msrp, ect..

Did I get a quasi-frankenstien Of this upper:
http://www.sigsauerguns.com/accessories/m400-516-upper-recievers/sig-sauer-m400-srp-ar15-upper-receiver-300-aac-blackout-uam400-300b-9-srp.html

Any insight would be fantastic.  I'll post some images after I get them uploaded.

It is not a Sig complete upper. It appears to be a Sig upper receiver at least. The rail is a $70 Chicom (link). Regular $7 A2 Flash hinder. $20 (maybe)Charging handle. No clue as to the barrel (although it's not Sig). You know the carrier. Unknown bolt.





If it shoots good and your happy with it that's all that matters.

 

I bought a 300 blackout kit from Daytona Tactical and it came with the same parts you have listed. The Sig upper, umbrella corp. BCG, and the barrel was marked just like yours.