Dillon Precision 20257 RL 550 Conversion Kit 338 Lapua .338 Lap Shellholder Review July 7, 2018October 26, 2018 - Corsairier Contains: Shellplate, powder funnel, and locator buttons. A conversion kit is needed for each caliber on the 550B. Conversion Kits can easily be installed in just a few minutes and change easily for fast caliber switches.