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I shot through a chronograph with my shotgun a couple of days ago and read a startling number on one shell. I wonder how accurate these rigs are with a fragmenting mass passing through them. Anyone know about this?
Chronographing shotgun loads
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I have been reloading shotshells since way before I was old enough to legally buy components. What I have found is that you have to do the chronographing when the sun is just right but without using skyscreens. I use both a Shooting Chrony and a Pact set up back to back so that I can verify the velocities. I set the first one up so that the muzzle is exactly 5 feet from the first reader on the chronograph, the two readers are 2 feet apart, so since the velocity number generated is the average between the two readers, the velocity measured by the first chrono is my 6 foot (2 yard) velocity. The second chrono I just look at to verify that the first chrono gave a good number.
The way I protect the front of my chronograph (yes the muzzle blast still hits pretty hard at 5 feet away) is to take a 25 round box of lead shot ammo and turn all the shells in it so that the brass is on one side, then I place the box directly in front of the chrono with the crimp end facing my shots on the small table that I built to use as a stand for front chrono, the second chrono is on a tripod, and is lowered so that the readers are about an inch lower than those on the front chrono, so it's pretty well protected too.
I don't think these chronos will reliably pick up the shadow of individual shot pellets from most sizes, but I know they will pick up a single BB from a BB gun, but anything less than 2 shot is questionable. So shooting at closer range is necessary since you are most likely to read the speed of your shotcup, and at a couple yards, it's still going pretty close to the velocity of the shot pellets, after about 3 yards, the difference grows pretty rapidly.
The way I protect the front of my chronograph (yes the muzzle blast still hits pretty hard at 5 feet away) is to take a 25 round box of lead shot ammo and turn all the shells in it so that the brass is on one side, then I place the box directly in front of the chrono with the crimp end facing my shots on the small table that I built to use as a stand for front chrono, the second chrono is on a tripod, and is lowered so that the readers are about an inch lower than those on the front chrono, so it's pretty well protected too.
I don't think these chronos will reliably pick up the shadow of individual shot pellets from most sizes, but I know they will pick up a single BB from a BB gun, but anything less than 2 shot is questionable. So shooting at closer range is necessary since you are most likely to read the speed of your shotcup, and at a couple yards, it's still going pretty close to the velocity of the shot pellets, after about 3 yards, the difference grows pretty rapidly.
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Ain't no one going to shoot a shotgun over my chrony!
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Yeah, I puckered up on the idea thinking I might have to buy the thing. I shot two different loads through it, and the first two shots were right on the money for the published data. Then the third shot, which was a different load entirely, including hull, powder, wad and shot size was fired through it. The expected speed was 1500 or so and it clocked in at over 1700. I hope that's wrong, because it was 1-1/8 oz of lead. That's rather brisk, even for Longshot data.
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The problem is likely the distance from the screens. I don't know how much muzzle blast effect there is from the shotgun, but I've seen a lot of guys report funny numbers, both high and low, that clear up when they move the chronograph out to 10 feet or more. One fellow shooting a .338 Lapua said he had to go to 18 feet before it stopped triggering irregularly. Mojo's use of two chronographs is one strategy for addressing this.
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