Just bought my first black gun, pretty excited. Get home and think "man I hope .556 or .223 is enough. Now I. Wondering should I get another barrel and convert this thing? If so what caliber? To further my ignorance I bought the heaveast thing I could find, workaday black match bullets.mm probably messed up there too. Any thoughts? I'm sure this subject has been beaten to death but I didn't see anything so I figured I'd ask!

Couple of questions
1 what you going to use it for hunting or plinking what type of animals if hunting
2 shooting past 200 yds.
3 suppressed or not
From here you will get advice
Cheap ammo 7.62x39 good out to 150 yds to 200
300 BO
6.8
6.5

Since you posted in the hog forum, I'm going to assume you are going after pigs.

You already have the complete 223/5.56 rifle so keep that for plinking, deer, varmints, etc.
It can be effective against pigs if you:
A. get right ammo for purpose
B. take selective shots where you can be sure of bullet placement - running shots with it is not advised.

Rather than changing the barrel, think about picking up an upper and just change upper and mags/ammo when needed.
Lots of companies have complete uppers ready to drop on your lower.
That way you can keep yours as is or change uppers/mags/ammo and have a rifle for a different purpose.
I've used 300BO, 7.62x39, 223/5.56, 458 Socom and 6.8 on the same lower without problems - just mark your mags on each side and don't mix uppers/mags.
With the 300BO, just like the 223/5.56 I would only take well placed shots and not runners.

.223 is fine for pigs as long as you shoot them in the head

Just add a 6.8 upper to your arsenal. You can have one shipped right to your door complete and ready to drop in your lower. It's just two push pins to change them out.

Make sure you order a complete upper with the BCG (bolt carrier group) and not a stripped one.

You will need to order a clip/mag with it as well.

.223 is fine.