I would imagine that the faster twist of the 223/556 barrel along with the slightly larger diameter would affect accuracy. My spikes uppers work great, I have thousands and thousands of rounds through one of them with very few malfunctions. I would say that a dedicated upper is the way to go.
I suppose it will at a distance, but face it, the .223 round is .224" in diameter, and a .22lr round is .223" in diameter. That equates to 1/1000th of an inch. In my opinion, hardly enough to be a concern unless you are shooting for distance, and/or you're shooting a gnat's eyeball at 100yds.
But for just can plinking, or bottle busting, it's gonna do fine.
Of course if you want more accuracy, you can buy a dedicated .22 upper, or buy a new .22lr rifle for about $160.00
Get dec. upper, this from a lot of long time experience, there is a lot information on this sub. do to the dist the bullet has to reach the rifling, and you get a lot of build up in the barrel, that will need to be cleaned to. this just for starters. Just my 50 cents. jj