Cooper Arms Model 21 in 19.5 Calhoon. The 19.5 Calhoon is a wildcat cartridge developed by James Calhoon of Havre, Montana, pushing .19-caliber bullets at extreme velocity for exceptional varmint performance with minimal barrel wear relative to the 17 Remington. Cooper chambers the Model 21 for it as a boutique offering for customers seeking maximum varmint efficiency in an unusual bore diameter. A truly niche Cooper chambering reflecting the company's custom-house willingness to accommodate specialty rounds. Type: Rifle Action: Bolt-Action Caliber: 19.5 Calhoon Capacity: 1 Year introduced: 1997, USA Weight: 55 oz Overall length: 41" Status: Active Intended use: varmint hunting