FN SLP MK1 Barrel Assembly 22" Inv Improved. The barrel is 22" and comes in a matte black finish. It fits a 12 gauge shotgun and weighs 3.15 lbs. It is produced and machined to the same quality and specifications of the factory FHN SLP barrels. The attached weaver rail allows for optics to be easily installed and to be removed with the barrel. Included iron sights make this barrel ready to use. The flexible magazine capacity reducers ensure that you have the correct capacity depending on the hunt.