You can actually load the .223 with 50 and 55 grain bullets using 1680, but you'll have to accept the case being only 80% full or so under the bullet. That won't prevent functioning or anything, but you can figure that there will be more velocity variation than you might want depending on whether the powder is nearer the front or the rear of the case when you light it up.
I ran a load of 2520 in .308 one year that was like that. Accuracy was not good until I deburred the flash holes to improve ignition. Deburring never made any difference I could detect with stick powders in that rifle (M1A), but they sure helped the 2520 a lot. About 40% reduction in group size at 100 yards. You may find the same thing in the .223 with 1680. It's something to keep in mind, anyway.
The old Accurate manual lists 45 grain to 55 grain bullets using 18.5 to 20.5 grains of 1680, with the exception of a 53 grain Hornady match bullet for which it lists 18 grains to 20 grains. QuickLOAD thinks it could go a couple grains higher, and that presents an issue to be aware of: Accurate used to multi-source powders more so lot-to-lot variation was greater than it is now. I don't know when your powder was made, so prudence suggests starting at 18 and working up while watching for pressure signs
Good luck with it.