Bat rolling breaks in the resin of a composite as if it were hit about 500 times. The flex of the barrel will increase when the composite is broken down; which equates to more distance. This type of flex is most common in men’s slow pitch bats but will happen will all composite bats, including youth baseball bats.
Youth baseball bats will have a shorter barrel than the men’s slow pitch bats. This shorter barrel will mean less flex across the barrel. There is not as much area for the flexing to occur. A composite youth that has been rolled will not gain as much distance as a composite men’s bat due to the difference in length. Distance that has been proven for a composite bat with 500 hits is about 20 to 40 feet. This is on a 34 inch men’s composite slow pitch stick and most youth bats are 32 inches and shorter. From experience, the difference in distance is about 3 feet less per inch. That would mean a 33 inch barrel would yield 17 to 37 feet, 32 inch barrel 14 to 34 feet, 31 inch barrel 11 to 31 feet, 30 inch barrel 8 to 20 feet, 29 inch barrel 5 to 15 feet, 28 inch barrel 5 to 10 feet, and a 27 inch barrel about a max gain of 7 feet.
These distances have not been scientifically tested but are based on feedback from the youth team staff. In addition, a number of composite bats will yield more distance than others will. Others factors that will decrease the amount of distance obtained is the material of the bat. It has been scientifically proven that double wall aluminum bats will reach the distance from bat rolling. There have been no scientific studies with single wall aluminum bats but feedback suggests some distance is gained. Double wall bats starts off at about 15 to 30 feet on a 34 inch bat and decreases from there. Aluminum bats gain about 5-15 feet on a 34 inch bat. There is no scientific information about aluminum bats but feedback would suggest there is an increase in distance.
Getting back to youth; if you have a 27 inch aluminum barrel and get it rolled what would be the increase in distance? The negative factors are length of the barrel and material. Aluminum youth sticks will gain almost no distance while a 27 inch double wall will gain about 4 feet and a composite will gain about 7 feet. This is why when people ask me about rolling shorter barrels I let them know the distance gained is not significant. Once the length of the barrel decreases so does the distance gained. The other factor is material; composite gaining the most, then double walled aluminum or alloy and then single walled aluminum or alloy.