I have a buddy with a spare 39M barrel (20" octagon, microgroove) for sale cheap and I'm considering using it as a replacement for the standard round barrel on my daughter's 39A Golden Mountie - nothing wrong with the old barrel, just looking to lighten the piece up some to allow her to shoot offhand a bit easier. Do these barrels have the same thread and would anything prevent the replacement? Not planning to junk the round barrel or anything silly like that. Any thoughts would be welcome!