Why? You'll have to re-chrono every time you swap barrels or chrono so one barrel shoots well and the other has low velocity. Another thing is that you'll never ever need a second barrel in 99% of situations. The only time I EVER need a backup barrel is when I break a ball and don't have a squeegie. Just carry a swab and you're good.
"There's nary a beast that can outrun a greased-up scotsman!" - Willie
"What makes a VM so charming is that you can chop down small trees with it" - Jaan