The problem with the long barrels isn't the loading. The problem lies in the balance. A small caliber, large barrel profile can be too heavy to shoot comfortably off hand. You can always lean the rifle for ease of loading. You don't want a lot of weight at the muzzle.
Of course, all this concern is of no importance when building an over-the-log rifle. For these matches where you shoot most often prone with the barrel resting on a log or chunk, you want a very long, heavy, stiff barrel with little or no flexibility.