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Hoo Boy. If they are old USGI surplus, it could be just about anything, including bent bbls. Like the man said, get really close, like 25 yds even, and set up the upper on sandbags or such, and look through the bbl with the BCG removed. When the bore is lined up with the bull, look at where the sights are. This might tell you if the front or rear sights are off.
Find a flat surface and place the upper on it, upside down. If the wings on the front sight base won't both touch flat with the carrying handle rails both touching, then the front sight base is off (this is assuming they haven't been bent). This usually because the bbl is not clocked properly (perfectly at 12 o' clock) in the upper. Possible broken bbl pin, or excessive play in the upper bbl pin slot. You can possibly fix this by un-torquing the barrel, inspecting, replacing the pin if necessary, lining it up properly if there is play in the slot, and re-torquing. Best done in a vise w/ bbl blocks. Put a reference line perfectly straight up and down on the wall. Line up the bore and rear sights on it. Use a mallet to tap the front sight base over until all three line up perfectly. Torque the bbl nut and re-check.
If the sights seem OK, in rough alignment with the bore, then the bbls might be suspect. In a perfect world you would have access to a bore straightness rod, which you could pass through the bbls to check for straightness. Also a bore errosion gage to let you know if these bbls are simply shot out.
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