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How to tell if a Chrony is giving good numbers?

 
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Old 02-06-2007, 10:15 PM
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How to tell if a Chrony is giving good numbers?

OK, I hate to start another "which Chrony should I buy" post. BUT [img]/ubbthreads/images/graemlins/smirk.gif[/img] , with my 338AM on order, absolute velocity is becoming more important to me.

I've had a "Shooting Chrony" since they first came out, and it has worked well as long as I made sure it was exactly in line with the bullet and was sitting far enough in front of the muzzle and the light was good. It even gives me reasonably close deviations when I am using one of my consistent load's.
But, just because it always shows my load to be within a small deviation, how do I know that all the readings aren't 100fps to high or low?

Is there any reasonable way to verify that a chrony is giving 'correct' readings?

If I knew someone else with a Chrony, we could set them up in parallel but if they gave differing (or similar) results, I'd still wonder if they were 'correct'.

I'd like to have an Oehler, but thats not in the cards, especially with the price of used ones. I'm debating about getting a CED Millennium and then setting it up in parallel with my 'Shooting Chrony'.

Has anyone used the CED with one of the optional/longer bars (4', 6', 8') ?? According to the marketing hype, they are very accurate?

I'm comfortable using my existing Chrony to get an idea of the consistency of my loads and that shooting 'at distance' is a necessity. But having the 'correct' velocity seems like a nice 'starting point [img]/ubbthreads/images/graemlins/wink.gif[/img] '. With my 338AM on order, I want to remove as many variables as humanly possible at the start.

One idea I had, was to take my bow to the local indoor range and shoot it over their Chrony (it usually repeats within 1-fps in my basement). Would that comparison have any validity at only 300fps vs 3000fps? If that comparison has validity, I could always go to 3 or 4 different ranges and get an average for all those chrony's; however I still wouldn't know which one (if any) was correct.

Oh well, enough rambling.

I guess it comes down to "is an Oehler worth 2-3 times a CED Millennium ?

Edited to add the following:
I just thought of another idea. How about setting up the chronograph so I could drop something through it from above. I could use a 50cal lead ball and should be able to calculate how fast it is going as it passes the sensors. I haven't done any calculations yet, but if I could drop it from far enough, it would give me a very good basis for understanding the accuracy of my existing chronograph. Again, I would need to understand how a low speed test relates to high speed readings.


Thanks,
Don
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Old 02-06-2007, 11:24 PM
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Re: How to tell if a Chrony is giving good numbers?

I use Remington "Target" standard velocity 22LR 40 grain solids to check my chrono.

Even though the ammo is not really target grade, and some rounds are noticably slow, it always averages 1150 fps for 10 rounds fired in my Ruger 77/22 with 24 inch bbl.

Federal Gold Medal Match is better ammo but I don't remember what the velocity actually is--and my notebook is out in the shop.

Jim
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Old 02-07-2007, 12:01 PM
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Re: How to tell if a Chrony is giving good numbers?

AJ- I dont know if you followed my post on 140g NBT at 800 yards out of my 7 RM, but I"m shooting about 3.5 MOA low at 800 yards. Now this could be due to several things, but I worked them all out that 1 day at the range. Like you, I have the cheap Crony, it gives what I thought consistent readings with good laods. This particular load averages 3250fps, this is about 3-4 differnt trips. With 3250fps and a .485 projected BC, I was hitting 3.5 MOA low at 800 yards. That just did not seem right to me. For that to happen, My velocity needed to be either 3075, or the BC of the 140g NBT was .350, and I highly doubt that. I was also told it could be my scopes click value was not really .250" but I later confirmed my scope was indeed true .250". I dialed 20 MOA up from 100 yards and shot at a big piece of paper. I should have been 20" high, well I was 20.5", close enough, problem solved there. Next I was told to zero at 100 yards and shoot 400 yards. According to ballistic program, I should be 20" low at 3250fps and .485 BC. Well I shot a nice little 1.1" group at 400 yards that was right at 23" low. So as you can see, its already off a couple clicks at 400, and about 14 clicks off at 800. Im thinking that my velocity is only 3075 because at 400 and 800, it matched up perfectly with the .485 BC. I need to look at getting a new cronograph as well. This could mean all my velocities are off. It could also explain why I'm always shooting at least 2-3 MOA low at 800 yards. I'm about 99% sure its my cheap Crony. I dont know anybody else around here with a Crony to verify either. Guess I just need to pony up the dough and get a better one. How are the PACT cronographs???
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Old 02-07-2007, 01:01 PM
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Re: How to tell if a Chrony is giving good numbers?

Has anyone used the CED with one of the optional/longer bars (4', 6', 8') ?? According to the marketing hype, they are very accurate?

AJ, About eight months ago I decided to up grade my chony,so I ordered a Pact Professional from midway.When I got it I was unable to get to work,after numerous calls to pact support,and still unable to get it to work I sent it back to midway,and exchanged it for a CED.The CED is easy to use,and works very well, seems very accurate.After having it for about a month(itching for more toys)I got the 4' bar,which also works good.The only thing I don't like is the 4'bar uses only 1 tripod,and is a little unstabe.If I had it to do over I'd get the 6' which uses 2 tripods,or the 8' which uses 3.
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Old 02-07-2007, 10:33 PM
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Re: How to tell if a Chrony is giving good numbers?

AJ,
I was going to do some bc calcs using two chronies. jimm sent me a donor chrony, old red one. About that time my own chony pooped out so I'm back to one. Thus I never got to calibrate one against the other.

GG shoots over the Oehler and Chrony at the same time to get the difference in velocities then puts the chrony out at 100 yds to determine bc.

One of these days I'll get another Chrony for that purpose. Chrony seems to work pretty well. I'd do the 22LR thing to check.
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Old 02-07-2007, 11:52 PM
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Re: How to tell if a Chrony is giving good numbers?

You can't really tell unless you have another to compare it with. The best thing to do is use what you have, applied the data to your ballistic program and do some longrange shooting. Note your drop and verify if it matches with what your program is telling you.
I had been using Beta chrony for a long time and I have no problem with it as far as velocity reading goes. The only gripe I have with Chrony is that, it is susceptible to reading error when someone else is shooting near you at the range. Other than that, they're okay. My friend has my chrony now and he still using them with great result. I bought myself a Pact Professional to replace the chrony. It's a tad better than chrony but not much.
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