Gas port location.
Any "standard" ar15 barrel that is long enough for NR requirements will be made for a longer gas system/port location. You can't buy a standard production barrel with a carbine length gas port unless it is a shorter barrel.
The factory WK barrel and the MRA barrel are currently the only options.
"Arguing with idiots is like playing chess with a pigeon..... No matter how good you are, the bird is going to s#!t on the board and strut around like it won anyway."
Youtube user Koyote Tan mentioned in his video about hoped parts commonality with his old AR180-B and the Brownell BRN-180 upper (someone from Wolverine should contact him, he probably be interested in parts from the WK and maybe even a whole rifle ) that his guide rod springs were worn out. This was causing failures to feed from the lips of metal magazines, so he exclusively used plastic magazines. A few people have noted issues with metal magazines and their WK, but the majority don't seem to have an issue. I wonder if those who are having problems with their WK feeding from metal magazines have problematic guide rod springs? Might be worth getting a replacement set from Wolverine/Kodiak for those having metal mag issues, as I expect it shouldn't cost too much to mail them.
I was having Failure to Extract issues so replaced the extractor and spring and added a washer and spring insert. Problem solved. So far, she runs fine with the mags that came with the gun and with 10 round polymer MFT LAR pistol mags.
It does NOT like my Tapco Intrafuse mags. Every second round failed to feed.