Back in the day, 26" barrels were the norm for Skeet, pump, semi or double. Through the 80's, 28" barrels became more popular for O/U's, with 26" the industry-standard Skeet barrel for both pumps & autos. In the late 80's with the introduction of Sporting Clays, more & more 30" barrels turned-up ... a length formerly found more conventionally on Trap & waterfowl guns, and with the introduction of "tube sets" from Briley & Kolar for the small gauge Skeet events, more & more turned to 30" O/U's for Skeet. A lot of the same folks found the 28" semi to be more their liking for the 12 gauge event, with even a few opting for 30-inchers ... the same semi they were otherwise using for Sporting Clays. Today, 28" and increasingly 30" guns in pumps & semis are probably the most common, as are 30" O/U's. Some are even using their 32" O/U Sporters as Skeet guns.
Bottom line ... leave your 28" barrels alone !