Hello, Gents! I am putting together a .223/5.56 gun for a "budget" SPRish build; one to save a little money on ammo and there aren't many ranges in my AO that exceed 600Y, anyway. Which 18" barrel would provide more accuracy/stability for projectiles in the 62-77gr range; a Stainless 1:8 .223 Wylde chamber or a regular 1:7 5.56 chamber? Thanks in advance!

Wylde is vastly better chamber in the accuracy department than *.gov 5.56*45
Wylde is a chamber that you can shoot basically anything.
There are better chambers if you are shooting match grade ammo ONLY.

62gr can be shot in a 1:10 bore (maybe even a 1:11 bore)
77gr needs the 1:8 bore
90gr needs the 1:7 bore (maybe even the 1:6.5 bore)

Next to chambering and crowning, the barrel is the least useful place to attempt to save money on a precision rifle.

anything you can mag feed through an AR will be fine in the 8.

Another vote for 1:8 and 223 wylde.  Im running a Green Mount barrels 18in 1:8 223 wylde and I almost exclusively shoot 77gr smks

To be fair, I've shot loads of 75 gr. Prvi out to 500 in a 1:9 barrel with great success. 1:7 is my preference, but I wouldn't turn down a quality 1:8 barrel.

1:8. If using TMK or Fullbore, hope it isn't a slow 8.