Is with this AR in the .223 would it be a good accurate coyote rifle out to 200 yards?
Yes, it would be a good choice.
I was wondering if this gun would handle a .450 bushmaster upper?
Technically it would, the upper takes almost all of the stress in an AR rifle. As to how well the two different materials (carbon fiber and aluminum) would fit together, I can not say. Your best bet would be to call Windham and ask.
The purchase of an M&P would probably be a better choice, but there are no guarantees.
I really like the lite weight and tight fit of the carbon fiber upper and lower of the C-15, but I would not consider mating two different materials together for a rifle I would use for hunting.
You may want to consider, instead of purchasing a second upper for a AR, you get yourself a Savage Axis in 308 instead. (also cheaper ammo) You are going to be limited to three rounds in the mag with any rifle you take hunting. The cost of the Savage Axis would be considerably less than the purchase of a second upper.
While I love my Bushmaster C-15 and know that carbon fiber will be the trend of the future (it is very sturdy) and many rifles are being made with it, many think it is still too new to the AR industry. (time will tell).
Like I said, a C-15 would be an excellent varmint gun, but that the Axis would be the way to go for a hunting rifle.
Good luck and stay safe.
Jim
Here is a picture of my Bushmaster C-15 (remember they only come with a 16 inch barrel).
This is what I use for long range hunting. Mossberg MVP - Flex