Big bore airgun hunting is catching on all over the country. The Umarex Hammer .50 caliber PCP is one such hard-hitting big bore air rifle that needs a big slug-like the UX SLA 388 grain hollow point slug. This soft lead slug is designed for maximum energy transfer and expansion. The Umarex Hammer has an actual bore diameter of .510 and the Umarex SLA series of slugs is custom made for optimal performance in the Hammer barrel.