What is the logic behind the idea that combo barrel lengths have to be different? If I like shooting a 30" o/u, why must the single barrel be 32"? Why can't I buy a combo where both barrels are the same length?
You can if you wish. When I bought my combo I wanted short O/U barrels (32 inch) for a fast swing when shooting doubles. I wanted my single barrel longer for a slightly slower, and more difficult to stop, swing.
I did think that the longer single barrel might come closer in balance to the shorter two barrel set up. Actually, my 34 single barrel feels just a bit heaver than my 32 inch two barrel set. I under estimated the weight of the K-80 unsingle rib.