I don't know if Wyoming has a mag capacity law but here in Missouri we do, so you can't hunt in Missouri with any rifle and use a high capacity mag.
Will a 223 work on deer, it sure will.
My oldest grandson killed his first deer when he was 8 years old using my AR in 223 caliber.
He shot a very nice doe at 175 yards and made a very clean one shot kill.
He was not using light jacket varmit bullets, he was using soft points designed for the task and he placed the shot well.
I was with him at the time and told him he could not shoot at a deer if it was over 200 yards away and he could not take a shot unless it was a good clean shot.
Do I use a 223 for deer hunting, no I do not.
The reasons why is, I know if I had a 223 with me that would be the time I would see that once in a lifetime buck at 400 yards and I don't feel the 223 cartridge is the right choice for that job.
Another reason is I have a decent selection of rifles to deer hunt with, my 280 being my favorite will most likely be the one in my hands.
As others have pointed out, limit the yardage you have to shoot, use a bullet constructed for the job, do your job placing the shot well and the 223 will kill your deer.
I recall seeing a documentary where Eskimos were hunting and killing Polar Bears with a 22 Hornet.
Best Regards
Bob Hunter
www.huntercustoms.com