\It's a fedarms upper. It's definitely a wylde. Clearly marked.
Using milsurp I have stocked up
I did fire some .223 through it and functioned fine.
Leads me to believe the throat is too tight.
Yes, you can open up a chamber on a barrel with a tight chamber. Look up Clymer tools and rent a mil spec. finish reamer. Last one I rented was about $45.00 plus shipping. Of course if you bugger it, you bought it, probably right at $200. Be sure you have or can borrow the correct "T" handle for the tool. Even hand turning a reamer, I like to do it in a Lathe (power off) and use a live center in the tail stock to hold everything in the best alignment possible and avoid any chance of chatter.
Before you take away metal that cannot be put back, do some careful measuring of that cheapie ammo, and make sure it is within the maximum spec. If you over ream to accommodate out of spec ammo, you end up with a barrel that is out of spec for any other.
Contact Tim Mellor at FedArms, they have a 100% satisfaction Policy. Found that on the Sig Fourms.
Fedarms FR15 - Topic
There is NO reason why a true Wylde wouldn't chamber 5.56x45 NATO. The chamber specs are so loose compared to an 855 round it's like a hotdog in a hallway.
As such, it's not a Wylde. Markings be damned, and reamer be damned. Overuse and/or too many sharpening trips.