Why do SXS barrel bore diamiters vary?

[SXS OHIO]

Wow...great info her. The reason I ask this question has more to do with originality than function. I have been wanting a hi condition graded small gauge....they are expensive! I wanted to know and be informed about this issue for value perspective. One of the guns that I looked close at has .010 over normal bore only in one barrel the other is correct. Most all the guns I buy are shipped to me after buying, no in hand inspections. As stated above when bores are not the same the flag goes up!??? I would prefer them to be the same, normal spec and still be choked properly. When old guns are priced 10-20K a feller has to know! Im still on a steep learning curve...(-: Buying is easy...selling with-out a big loss can be very tricky. Like John Wayne said...Life is hard and its harder if your stupid!!! Thanks all SXS ohio.............................