Good thing to test also is see if you are already getting "full burn" with the current 24 inch. If you are then you are wasting money having a longer barrel put on. You would actually lose a little speed.
Good way to test is to take an OLD white sheet ( I say old in case your married..Dont wanna pee off the wife ,) ) Lay it on the ground longways toward target, get in the prone position with the end of the barrel about 2 inches from the end of the sheet, and about 6 inches up. Let a round loose and see if there is powder on the sheet. If there is then you could either reduce powder charge or longer barrel. If there isnt then the only need for a longer barrel is if you want to increase your powder charge with the same burn rate powder, or if you want to go with a possibly slower burn rate for more pressure. Some calibres do better with a slower charge while some like a faster burn. Its all dependant on the rifles and calibres.
Here is a very handy and effective device I use to dispense corn with - but it could also be used to dispense any other seed or deer feed.
I had an old feeder that had a failed motor... I made a set of brackets to attach the feeder to the rear of the 4 wheeler - the lower one encircles the feeder and has a forward section with holes drilled in the outer ends of the bracket... these holes align with two 5/16" bolts that drilled into the rack of the 4 wheeler.
The upper bracket is an "L" shaped...