Several manufacturers marked their barrels with the ordinance bomb either near the date, on the side near the gas piston or on the side near the breech. They include Winchester, Underwood, IBM and Buffalo Arms. Rockola used their own barrels and as far as I know did not mark them with an ordinance bomb. Can you post a picture of the date and ordinance bomb?
HI; I looked at it again on the left side of barrel says not blue sky but just e sky and just behind the front sight says um.co and 43 with the ordnance and under the rear site says rock-ola #1687793 THANKS.
Cali's right. The BLUE SKY stamps are usually very clear. What you describe sounds like part of the stamp was removed. Also, it sounds like part of "I.B.M. CORP." behind the sight was also partially removed. If this is the case then you have a replacement barrel. We really need to see a picture of this to know for sure.