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.
Want a quick and inexpensive call for Moose? Take an empty 32 ounce coffee can, and make a small slit in the bottom, only about a quarter inch. Then, take one of those really big red rubber bands, the ones that go around big folders. Cut the rubber band to make one long piece.
Now, thread one end of the band and tie a knot on the outside of the can so it won't pull through. Cut the band off on the other side so it is even with the top of the can.
Now, wet your finger,...