RCBS #90304. RCBS Case Trimmers are designed to be user friendly and provide very accurate results. These shellholders are required to hold the brass cases while they are being trimmed. Works with: RCBS Trim pro, manual and power case trimmer only. Fits:.257 Weatherby Magnum, .264 Winchester Magnum, .270 Weatherby Magnum, 7mm Remington Magnum, 7mm Shooting Times Westerner, 7mm Weatherby Magnum, .30-338 Winchester Magnum, .300 Holland & Holland Magnum, .300 Weatherby Magnum, .300 Winchester Magnum, .308 Norma Magnum, 8mm Remington Magnum, .338 Winchester Magnum, .340 Weatherby Magnum, .350 Remington Magnum, 9.3mm x 74 Rimmed, .375 Holland & Holland Magnum, .416 Remington Magnum, .450 Marlin, .458 Winchester Magnum.