I have a few uppers I want to swap around....my question...
I have a oly upper nothing special but it has a regular front site.I am going to replace it with a shaved set screw block....be there do that no problem....
But the regular site base will then go on a lightweight barrel that has never had a regular sight on it...(it had a shaved block that attatched with setscrews)...so will I need to ream the front site pin holes..or can I just pound them back into place....I thought it better to ask than to turn this into a LOOK WHAT I FUBARED THREAD...

Yes. You will need to taper ream the holes because, by design, the pins partially pass through the outer circumference of the barrel.  This is what keeps the front sight from moving once the pins are driven into place.  This is a tricky thing to do since you need to make absolutely sure that the FSB is aligned with the indexing pin back on the barrel extension before drilling and taper reaming.  Otherwise you will end up with the famous "canted" front sight.