A Wylde chambered 1:7 generally is a great match for a 223. Given, there are better chambers if you like to just shoot tiny groups at 100-300 yards on paper, but, remember a Wylde chamber can allow XTC shooter to hold a 6" X ring a 600 yards with irons.
I would...
1) Call McGowen, ask them for a reamer print for their Wylde chambering. Check the twist with a tight patch on a cleaning rod. A 1:14 twist won't shoot much longer then a 52 grainer.
2) Load a 80 SMK or the like long in a dummy cartridge (no primer or powder), chamber carefully and look for rifling marks on the bullet, clean the bullet with 0000 steel wool, seat it a bit more and look again, repeat until the marks just appear, then are gone. That will give you a pretty good idea where the rifling starts.
3) With the barrel in the stock, check the action screws, the should be ~ 60 inch pounds using a torque wrench.
4) Check the barrel, is it free floated? Can you run a dollar bill all the way under the barrel to the action without any binding?
5) Is the action bedded? Should be for best accuracy.
6) Check the muzzle for nicks (mentioned in previous post)
7) After firing do you get a lot of copper while cleaning?
8) Scopes hold their own issues, several mentioned in above posts, good base and rings are a must, rings torqued to about 18 inch pounds, Cross bolts on rings ~60 inch pounds.
9) If all these check out, load a 69 or 77 SMK, jumping them ~25 thous. to the lands, with 23 grains of Varget and a Rem 7 1/2 primer (load is a little lighter than match loads, but a good start)
10) Shoot these from a very clean barrel, firing 5 shot groups from a solid rest. Most rifles will shoot a little better after they dirty up a bit. Shoot at least 5 - 5 shot groups and compare results. Go from there for better load and accuracy testing. If they shoot lousy, try a different bullet and or load, repeat.
Trying to find the accuracy problem isn't easy or much fun, not all barrels of all makes shoot really well, it's bit of a crap shoot sometimes. Pretty frustrating when you plunk down good money for a name brand barrel and it won't shoot.
Now, a HM friend ordered a 1:12 308 for Palma, he got a mismarked 1:18 twist, designed for a 30 BR, Could not understand why it keyholed 155 SMKs at 100 yards. I had a 1:10 Hart that would hold the 10 ring at 800 yards with any bullet I tried, but nothing better then the 10 ring and all of it. Can't win F-T/R matches with a >1MOA barrel, it's gone now!
Good luck.
