The pressure is far more important than the hull length. Use a loading manual load of 7,500 psi or less and the extra hull length will not matter enough to matter. There are plenty of loads that are sub-7500 psi. Also, use light shot charges, say 7/8 oz, for low recoil. Low pressure is kind to the metal and low recoil is kind to the wood and the shooter.

These old guns are a hoot to shoot. But, being a bit long of tooth, they require careful considertion for their dietary needs.