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20 Fergusson Ace is a wildcat centerfire rifle cartridge based upon the 20 BR which has a blown out shoulder angle of 45 degrees. It was designed and developed by legendary gunsmith and varmint hunter Gaylon 'Ace' Fergusson and predates the .204 Ruger factory cartridge. Having the blown out form and steep shoulder angle the Fergusson Ace family of cartridges have approximately 10% more powder capacity than their parent cases. This gives very high velocities when paired with the correct propellant blend and charge. An example round recorded 4220fps with a 40 grain V-Max when fired from a 24" pac-nor 1-11"twist barrel. This performance comes at the cost of the barrel with life expectancy in around 500-600 shots depending upon the choice of steel grade. Brass is usually taken from .22 BR Remington stock, then necked down to .204" and fire formed in the custom chamber of the rifle. Major drawbacks are the scarcity of both reloading dies and chamber reamers in this format.
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