Friend has a Vulcan model 47..
Has less than 100 rounds through it, been a closet queen
Says it will randomly while functioning fine, have it properly eject, feed, but hammer won't be back.
I don't have any experience with AK FCG. In an AR that would signify a problem with the disconnector. Any suggestions fellas?
He dropped it off for me to look at. I can post pictures as necessary etc
Thanks in advance

If the rifle fires, the bolt operates and feeds another round into the chamber, but the hammer isn't cocked, it's the disconnecter.
The disconnecter is failing to catch the hammer and the hammer is following the bolt down.
This is NOT SAFE.  DON'T fire the rifle until you get it corrected.

The correct "fix" can depend on what brand or make the trigger unit is.
The "usual" is to stone the bottom of the disconnecter to allow the top of the disconnecter to tilt farther forward so it properly catches the hammer.
You want quite a bit of engagement of the disconnecter with the hammer to insure you don't get doubling or firing when the trigger is released.

Another easy fix is to just replace the entire unit with a new Tapco G2.

Once you get the trigger sorted, keep a close eye on the ejector. Some Vulcan rec's had proper heat treating for hardness but they over looked the heat treat on the ejector rail. You may see it mushroom. If so break out the MAP torch and harden it -- just the ejector. You don't need to do the whole rail.