Re: 20Gauge shotgun slug
.615 is the nominal size but it varies among manufacturers. If it's a Foster or Brenneke rifled slug don't worry about it, the only choke you have to worry about is super full choke, ie. turkey choke. If it's a little over size it will swage down harmlessly in your choke and if its a little undersize the full choke will help you shoot it more accurately. I have one on my desk in front of me and it only measures .610. I don't think my gun notices the difference.
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