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measuring shotgun chokes

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3 comments

  • mark christian
    Gauges and micrometers are suitable for a "ballpark" choke reading. The only way to truly determine the actual restriction shotgun barrel is to shoot it, typically at 40 yards, and count the percentage of pellets falling within a 30" circle placed at the center of the pattern. Once the pattern is determined you can then figure the choke using a set of tables, which I don't have in front of me. If I recall improved choke is 55% and then the restrictions (improved-modified, modified, full and extra full) go up by 5% increments until you reach 75%, which is extra full.
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  • zimmden
    Mark is right on. Shotgun chokes have been an inexact science for 150 years. Markings are an approximation of what can expected. Shot hardness, size, wads, pellet speed and brand of ammo are variables in addition to choke dimensions. Patterns at 40 yards is the true yardstick of pattern size and quality.
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  • MIKE WISKEY
    the AMOUNT of choke is determind by the AMOUNT of consriction at the end of the barrel (about .010" per degree of choke, with stops in bewteen). Most 12 ga. barrel are about .729" so a choke consriction of .010" (.719" muzzel dia.)would be about imp. cylinder. the problem is barrel dia's. vary wildly, I've had 12 ga. barrel that measured .740" and others that measured .720". like mark said the only way to truely determine what you have is to pattern the shotgun and that only holds true for that particular load. change the load and your pattern can change.
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