Playing with my new Alpha chrony...

rdelliott

rdelliott

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So I got out to the range today to test out my new Alpha Chrony. It worked as advertised, but what disappointed me was the variation in muzzle velocities from my .303 reloads. They were 37.3 grains of H4895, measured by one of those little red Lee beam scales, and while the variation was relatively speaking half as bad as the Remington Golden Bullet .22 LR I tried, it wasn't as good as the Czech 7.62x39 I also tried, measured by dividing the extreme spread, or difference between the highest and lowest velocities recorded, by the average velocity.

I guess I'm wondering how much variation in muzzle velocity should I expect? Is 5% acceptable? If not, would buying a better scale be an easy way to fix the problem?

Also, how accurate are Alpha Chronys out of the box? There doesn't seem to be any way to calibrate it. Do these things mismeasure?
 
Standard Deviation

I'm not sure what is causing your range of velocities, but the more typical measurement for this is Standard Deviation. It is easy to calculate if you have all the values, and generally much more useful with more values than less. I try to shoot at least 10 rounds under the same conditions when attempting to measure this.

Snapshot
 
rdelliott said:
So I got out to the range today to test out my new Alpha Chrony. It worked as advertised, but what disappointed me was the variation in muzzle velocities from my .303 reloads. They were 37.3 grains of H4895, measured by one of those little red Lee beam scales, and while the variation was relatively speaking half as bad as the Remington Golden Bullet .22 LR I tried, it wasn't as good as the Czech 7.62x39 I also tried, measured by dividing the extreme spread, or difference between the highest and lowest velocities recorded, by the average velocity.

I guess I'm wondering how much variation in muzzle velocity should I expect? Is 5% acceptable? If not, would buying a better scale be an easy way to fix the problem?

Also, how accurate are Alpha Chronys out of the box? There doesn't seem to be any way to calibrate it. Do these things mismeasure?
Click to expand...

First thing. Your Alpha chrony does SD, but you know that already. Secondly. I just got mine and the first thing I did was place it behind my buddies chrono to compare. There was about 30 fps difference. I thought that was quite a bit. Other than that mine seems to work fine. It's funny how some loads work well and some don't. My 338 WIn mag has an ES of less than ten FPS sometimes on a 4 shot string yet my 223 has about a 60 FPS. The ES and SD is much like what I was getting on my buddies Chrono so I think my Chrony is fine. I'm kind of new to reloading, but that's what I know! The other thing I can tell you about the Alpha chrony is you want to set it back as far as possible when using the big boomers. My 338 win has blown it apart more than once:)

G
 
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I have added a couple of LED lights mounted above the sun shades.

I have found that a consistent light source helps greatly in getting consistent numbers. Although, I would still shoot some known/expected velocity rounds over the chrony first to ensure the numbers are what I would expect.
 
Bare in mind, chrony data is not a measure of accuracy, just cause the Velocity reads off doesn't mean it's not a good load.

Chrony is handy for load tuning. I've had loads that would shoot a 0.2" @ 100y but read quite the variation on the Chrony.

As far as the accuracy of a chrony itself, I've read they can vary. You'd be paying 1000's of dollars for a machine that would actually tell your the exact FPS of your bullet.
 
I had took mine out yesterday, had some pretty accurate shots, but I do have an electronic scale, some powders have differences, others could be seating depth, light into the chrony if a cloud goes by, neck tension etc, the list is long
 
Except in quite small capacity cases, small powder [+-.2 gr.] variations are not the likely cause of your velocity differences.

Your Chrony is probably accurate enough to get you to a valid conclusion on your loads.

Watch things like neck tension, powder position in the case if the case is only ¾ full, seating depth, etc.
Additionally, changing light conditions can alter readings somewhat.

Don't bother including the first shot out of a cold, clean barrel, either.
It will skew the results.

Regards, Eagleye.
 
Just a tip...Make sure your chrony is at least 10 feet from your muzzle with normal calibers....and about 15 with mag calibers....otherwise you may get scattered readings caused by muzzle blast.
Jim
 
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