Range Report How far out to set the chrono?

ReaperDriver

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    How far out do you guys set up your chrono's? I was at the range the other day and ran a bunch of loads across my CED M2 from my AR. I put the chrono at about 10 ft and was getting quite a few "no read" errors. When I got home, I re-read the manual's troubleshooting section and it said that maybe I was too close and muzzle blast was interferring with the sensors. DO you chrono gurus set up further away? What's a good distance?

    Follow up question: What program or formula do you use to compensate for the distance to give you true muzzle velocity? I tried a poor man's approach with JBM by setting the range readouts to 1 ft increments and then played with the muzzle velocity until I got the chrono velocity to be correct at the 10 ft distance. But that's a PITA. Is there a better way to calculate actual MV?

    Thanks!
     

    chosen_karma

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    Re: How far out to set the chrono?

    Chrony's can be tempermental depending on the type you use, as far as the distance from the end of the muzzle, I have done barrel ballistics testing on the 5.56 M-4 with the chrony 4 ft from the muzzle without any issues. If you arent using a squirrel cage on your weapon you may have to adjust that distance (due to muzzleflash)The key thing, and I know it sounds retarded, is to make sure you have your chrono facing the right way, and observe the ambient light as this will have an effect on the chrony "eyes",if it is bright and sunny you need to use the diffusers, you also have to ensure your round is traveling 4-6 right over the eyes. What I have found to be the easiest and most accurate is to use a solid cradle or vise, use a LBS (laser bore sight)to help you determine exactly where the round is going to travel in its flightpath, then adjust from there, whether its your weapon or your chrony.

    As far as your MV question, there are several calculators/programs,I use the KAC ballistic computer on my Iphone at the range and it seems to be pretty damn on. Several ammunition manufactures have that data readily available as well. As far as a "true" MV, well thats is going to take you moving your chrony back incrementally until you reach your desired range, keeping in mind you are going to have to understand the actual path of the round (rise and fall),barrel length, twist rate, ect...ect.. PITA!! I have several downloadable programs you can try if you like.
     

    azimutha

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    Re: How far out to set the chrono?

    I've found that from non-prone positions 10 feet is okay but firing prone, even with a tarp, kicks up dust and debris onto the sensors. No problems backing it up another 10 feet as long as I remember to tell my ballistics program it's 20 feet away.
     

    kraigWY

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    Re: How far out to set the chrono?

    I would go as far as necessary, maybe 30 feet, (if you can keep from shooting your chorny). Main thing is consistant. Shoot the same place.

    If you want to see what your MV is when you are X distance from the Chorny, Hatcher's Notebook (which every serious shooter should have) has a fomular to convert your results at distance to MV.

    I'm not in a postition to dig my copy our right now or I'd post it.
     

    ChadTRG42

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    Re: How far out to set the chrono?

    I also use the CED M2. At a minimum, I set it up about 12 feet away, which is 4 big steps for me from where the muzzle will be. If I am shooting a big magnum with no brake, then I'll move it out a little further to about 15'. 95% of my shooting is done prone. The muzzle blast can/will effect the chrono if it's too close. Also, if it is a cloudy day, I will leave off the sky screens. If it's sunny, then have them on. If you have the IR screens on and it's sunny, this will also cause errors, since the IR and sun interfer with each other.

    I use this ballistics program for almost all my trajectory. The program allows you to enter the distance of the chrono.
     

    Deisel

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    Re: How far out to set the chrono?

    Chad, if you are shooting prone with the M2 do you shoot so the bullet passes though both screens at the same height or it is OK if the bullet is on an upward trajectory though the 2 screens?
     

    RECKON SO

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    Re: How far out to set the chrono?

    I also set my CED M2 as far away as the cords will allow. I just remember to tell the program how for that is. As far as light screwing around with the sensors, I have built a sort of "dog house" out of PVC pipe and strechted a tarp over it, I put the chrono inside this every time because Im using the I-R screens I figure sun or no sun the sensors are seeing the same thing every time. I cant prove this is any improvement in readings but I dont get errors no matter what the weather is doing "even when its raining!". Just my 2cents
     

    Rob01

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    Re: How far out to set the chrono?

    12-15 feet has always worked for me.
     
    G

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    Re: How far out to set the chrono?

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ReaperDriver</div><div class="ubbcode-body"> What's a good distance?</div></div>

    When grabing data for a new load I do 5 yds first, then set it at 100 yds, then lastly shoot threw it at 200yds(200yd range is only 10min away). Take the data home, run and play with all the numbers with the Sierra program set in 5 yds increments.
    It has always worked well, and always gets me on steel, after which, the true info gets logged into that rifles book.
     

    TiroFijo

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    Re: How far out to set the chrono?

    10 feet may have some (rare) problems due to blast in rifle calibers

    12-15 feet always work with rifles

    handgun calibers you can put the chrono closer, 8-10 feet
     

    Greg Langelius *

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    Re: How far out to set the chrono?

    Two things to rememebr.

    After setup, but before firing; boresight to ensure you're not gonna drill the chrono. Always provide a target to aim at, and ensure that this aiming point doesn't endanger the chrono.

    Be aware the bullets sometimes shed bits, like sabots or gas checks. These can also wipe out a chrono.

    Don't ask how I know...

    IMHO, ten feet may be a tad close, and twenty feet is probably a bit far.

    Greg
     

    Short-bus

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    Re: How far out to set the chrono?

    I set mine today just a touch over 7' to the first sensor, I thought it was a bit further but my shooting partner today had a tape measure. We also ran back to back my Beta Master Chrony with his Pact behind it to check similarity in readouts. All readings were within 1% of each other. Sometimes there were some readings that went a little haywire, but those only came after a bullet strike on the uprights that hold the skyscreens on. BTW, it wasn't me that hit 'em, but the chrono was still working fine for the most part after that, and worked just swell after I put the skyscreen back in place due to it flying off.

    BTW, anyone know where I can get a replacement metal bar for the uprights to the skyscreens?

    Branden
     

    ReaperDriver

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    Re: How far out to set the chrono?

    Thanks guys. I think I've been setting it too close. I was probably at about 9 feet (3 steps) and I was getting lots of reading errors (i.e. no data) over the sensors. Next time I'll go to 12-15 and see if it reads more consistantly.
     

    vman

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    Re: How far out to set the chrono?

    I stretch my chrony out as far as the chord will go between the controller and chrony unit.

    If i bring it in much closer the muzzle flashes from the benches next to me tend to set off my unit
     

    bohem

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    Re: How far out to set the chrono?

    My chrony doesn't have a remote unit, so I stick it a good 20-25 feet from the muzzle. They're pretty sensitive to muzzle blast, this allows me to greatly reduce the number of "Err &#65297;" returns.

    Measure the distance and make a note of it (a regular 25' tape works well) and drive on. I put 47 rounds over it this evening without a single error, it was sitting at 27' 7" away.
     

    Leaddog

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    Re: How far out to set the chrono?

    10 feet from the bench. I shoot prone, but when I chrono, I use the bench. I've never had a problem at 10 feet and get good consistent readings with my PACT MK IV.
     

    el gordo2

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    Re: How far out to set the chrono?

    Usually about 12f off a bench indoors with IR screens. I have even set up as far as 600yds with my CED M2 just to see the actual results at that distance.
     

    GardDog

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    Re: How far out to set the chrono?

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Dust_Remover</div><div class="ubbcode-body">
    BTW, anyone know where I can get a replacement metal bar for the uprights to the skyscreens?

    Branden </div></div>

    I replaced the two piece bars that came with my Chrony Beta Master with a solid length of metal rod. I took the factory rod to Home Depot and found the metal rod that matched the diameter. Took it home and cut it to length with my Dremel.

    On topic, I use 10 ft for standard loads and 15 for my WSMs.