I have an upper that has an "A" in front of the windage knob.  The top point of the "A" is seperated from the main body of the "A".  Is this an Oly, a Bushmaster, a government contractor, who.  Thanks in advance.

The "A" isn't a Manufacturing/Machining designator, its a raw forging designator.
That's the co. responsible for forging the Al, into a rough (raw) forging (shape) that will later get machined into an upper by 1 of many manufacturers and/or machine shops.
The forger  I can't identify, though someone will be able to for you...
You won't be able to positively ID the machine shop/Manufacturer by the Raw Forging co, but you will be able to eliminate 1 or 2 if they never used that RF co.



/S2