The barrel length will determine wheather you can shoot a 150 grain pellet charge or 120 grain loose powder charge. The 26" barrels are classified as MAGNUM and they were made with both the 7/8" and 5/8" breech plugs. They all are made with the same exact materials, so they would all be the same strength, but the 24" barrels are only rated to 100 grains of pellets or loose powder by volume. The 26" barrels have a better chance of burning the full charge of the MAGNUM loads.
So to answer your question, yes if it is the 26" Magnum barrel. No, not recommended for the 24" barrel although the barrels are made of the same materials. All the loads in the owners manual are RECOMMENDED loads for accuracy not maximum safe loads.