My rule of thumb for being able to move the front sight (rotating the barrel in the upper) is that the rear sight must be able to be adjusted to zero out the rifle (with room left between the rear sight and sight housing side wall). Since you rifle/rear sight has run out of room to zero, it's time to pull the barrel and check it out. By trying to just rotate the barrel so the front sight is in the correct position, you stand a chance of rotating the feed lips and bolt entry channel (lugs) out of position for clean engagement.
Where you want to start, once you have the stripped barrel in hand, is to make sure that the barrel extension pin is on the same index line as the front sight tower, and the pin is not bent. If there on the same plain and the pin is not bent, then using a receiver block to hold the receiver in the vise, pick a point at least 25' way to look down the barrel bore, then the sights (a bore laser keeps you from having to look down the barrel). Once you have the center rear sight/front sight tower seeing the same point as the bore, you can shim the extension pin in the receiver to keep the barrel from rotating during tighten, or just tighten up the barrel is the pin is tight in the receiver socket slot. Then once you have the rifle back together, use a leather mallet to slip/rotate the barrel in the receiver to fine-tune the front sight so it and the bullet point of impact are seeing/reaching the same point.****
NOTE: WE DO NOT USE THE MALLET TO DRIFT/ROTATE THE FRONT SIGHT ON THE FRONT OF THE BARREL, JUST TO SLIP THE BARREL/EXTENSION IN THE RECEIVER.
What I have not covered was if the barrel extension pin and front sight are not on the same plain. Depending on the amount of index the two are off, will determine the way to correct the misalignment.
Bottom line is that you will need to pull the barrel and check the extension pin and sight tower indexing out.
If you lack the tools, post in the hometown forum to see if anyone around you have the tools, and can give you hand pulling apart the upper.
*** Each type of ammo/manufacture will shoot to a different point down range. Before you begin to fine to a rifle for a dead center rear sight, make sure that the ammo being used for final tuning is the same that you will be using for a while. If you game plan is to use different types, then fine tune the front sight so that for the majority of types of ammo, you only need to adjust the rear sight a few clicks off center (left or right).