I have three .62 caliber flintlocks--two with 42" barrels and one with 24" barrels--(it's a swivel breech). Recoil is less with the swivel breech due to it being a bit heavier than the other guns. I think weight rather than barrel length is a better recoil reducer, all else being equal.
Now, muzzle blast is another thing altogether. The swivel breech gives a nice bark indeed!
Dan