i bought a chrome lined DPMS 14.5 M4 barrel from CMMG  (great service by the way) and i noticed a pronouned bur in the barrel. after some judicious brushing i have removed most but not all of it. it appears to be from the drilling of the gas-port.  i have heard of this before not i havent encountered it. is it ok to shoot, or should i scrub more or what????

Yes, the act of drilling a gas port sometime leaves a little sharp edges.  I wouldn't worry about it.  Had the same thing in my OLY SUM barrel, shot 5 rounds through and it was nicely "de-burred".

Don't worry too much about the burr.
If the barrel had been factory installed on a gun, it would have been test fires and cleaned, and you probably would never have noticed.
That being said, don't be too surprised down the line if an armorer ever drops a milspec "barrel straightnees gauge" down you bore, and it hangs up in the area of the gas port. Your barrel is not bent, but over time a little deposit of copper jacket material may build up at the burr and make the "straightness" gauge stick.
Unfortunately most armorers don't know this and many otherwise serviceable barrels are then replaced unneccessarilly.
In fact, if we had known this in 1980-1983, we would not have increased the barrel diameter in that area on the M16A2.
ColdBlue sends...