Chronograph Errors!

6x47

Member
I had a cracking day out shooting with WMS in Wales yesterday; very good day and very informative (if a little wet). But not without its shocks...!

I was using my 6x47 lapua and throwing 105gr rounds down range at a chrono'd 2855fps. Using 2 ballistics programs that Andrew (the WMS chap) and I had we could not calculate the elevation and windage for any ranges beyond the zero distance with the figures I had speed and BC. Through a series of calculations and tests at ranges from 100yds to 644yds we finally calculated that the rifle was throwing out rounds at around 3125fps! That is a serious chronograph error of 270fps!!!

Has anyone else had a similar issue with inaccuracy of their chrono that they are aware of?

Al
 
I would not be amazed with 11.5% error. I think people overestimate the accuracy of these instruments.

Did you check against another chronograph?

Are they ever calibrated once they leave the factory? Are they even checked there?

What accuracy do they claim? What if the batteries are going flat, does that alter anything? What if it has sustained slight damage or a minor twist?

So many factors that could cause a greater error. It's all ballpark.
 
The rounds I had were my standard loads that have always been velocity accurate through my chrono +/- 10fps. I didn't have the chrono with me as I thought I knew what the load was doing. Really glad we took the time to work through the errors. Just amazed at how cr4p my chrono is!

Al
 
From memory both Chrony and ProChrono claim 99.5% accuracy. I've no idea what their QC is like, though.

I suppose if there was some other possible explanation for the discrepacy between the recorded velocity and the observed ballistics, the WMS folk would have sussed it out.

Pedantry corner:
The round goes into the chamber, but ceases to exist once the primer has ignited.
The bullet then makes its way to the target.
;)
 
From memory both Chrony and ProChrono claim 99.5% accuracy. I've no idea what their QC is like, though.

I suppose if there was some other possible explanation for the discrepacy between the recorded velocity and the observed ballistics, the WMS folk would have sussed it out.

Pedantry corner:
The round goes into the chamber, but ceases to exist once the primer has ignited.
The bullet then makes its way to the target.
;)

The chrono I have is a ProChrono. I think that I may do some more testing to try to establish the actual error before complaining.
I will ignore the Pedantic commentary as the point of communication is to be clearly understood [Ref Steven Fry 2012] :D
 
I had the same fault some time ago with my prochrono some of the ds2 lads were borrowing it , i was about to shoot it as a bad deal but it was to wet to get to there location i told them i would pick it up as soon as pos ,but by the time i got back to them it had stopped raining and dry'd out the chrono worked fine with no errors coming back as before ,i think it just did't like getting rained on bit like all of us! Now reads ok and compares to the data on the target as per the computer readouts within 1/2 inch. 2p worth try doing a ladder shooting at said ranges see if they match



The chrono I have is a ProChrono. I think that I may do some more testing to try to establish the actual error before complaining.
I will ignore the Pedantic commentary as the point of communication is to be clearly understood [Ref Steven Fry 2012] :D
 
I'd expect the spread to be pretty low as these chronographs are timed with a simple count down clock and crystal.

The pdf download says "+/-1% of measured velocity, or better" so I'd call that about 30fps either way.

Have you run some fair grade 22LR over it? They should give you pretty low (10fps) spread and something like Winchester subsonic is close to the 1055fps most of the time.

When you chronographed the loads were they within, say, 50fps spread? Just wondering if the unit is behaving or having an off day. My current Chrony Master has sulks under some lighting conditions but is generally very precise and consistent (as my loading).

I had a discussion with a colleague a few years back an he insisted on checking my data with his very expensive calibrated unit: the CED I had at the time was within 2fps and just as consistent.

Best of luck as they're fussy creatures but useful sometimes.
 
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I will give my unit a go with my 22LR, thanks for the recommendation.

In terms of lighting, what are the best conditions? Overcast, sunny etc. Would it be worth putting a cover over top of the beams?

Al


I'd expect the spread to be pretty low as these chronographs are timed with a simple count down clock and crystal.

Have you run some fair grade 22LR over it? They should give you pretty low (10fps) spread and something like Winchester subsonic is close to the 1055fps most of the time.

When you chronographed the loads were they within, say, 50fps spread? Just wondering if the unit is behaving or having an off day. My current Chrony Master has sulks under some lighting conditions but is generally very precise and consistent (as my loading).

I had a discussion with a colleague a few years back an he insisted on checking my data with his very expensive calibrated unit: the CED I had at the time was within 2fps and just as consistent.

Best of luck as they're fussy creatures but useful sometimes.
 
British lighting? What a laugh! I live in the far North and so this time of year anything between 1000 and 1400 provided it's not raining or snowing!

The shields that go on top of the unit are needed when you have blue sky or broken cloud: the real sky colour is pretty "black" and so the plastic bits give the plastic bits give the photosensors something to look against.
If you have moderate overcast it'll work well without them. If it's very thin cloud then they might as well be left on.

I've just done a quick look at the spec data at Pro Chrono Digital
and if they're using a 1.3MHz crystal then even the most crappy grade will barely give a 1 or 2 fps error if my sums are right.

This make sense?
 
This is a post I made on UKV yesterday (copied and pasted here) after comparing my new Magnetospeed and my old Chrony F1. Thought it may of interest to some.
------------------------------------------------------------------------------

A couple of days ago I ordered a Magnetospeed V2 chronograph from Brian Fox whch arrived this morning. I paid a very reasonable £299 delivered, it was sent by 24 courier but few things make it up here in 24hours!

Anyway I've been using the same Chrony F1 for the past 10 years or so and I was always reasonably happy with the data it gave me, verified fairly well by bullet drops at long distance.

The reason I bought the Magnetospeed was its reputed to be thoroughly accurate, is totally unaffected by light conditions, gives true muzzle velocity instead of 10-15feet away and is quicker/easier to set up, stores all shot data directly to the included SD card and available for immediate review including SD, ES, average FPS and Chrony F1's and other cheap chrono's often are perceived to be are crap and tell lots of lies!!!

This afternoon I grabbed the .223 and ten rounds of ammo anxious to put a few shots over it and the F1 simultaneously to prove to myself the F1 is an out and out liar!

Shots 1 -10:
---V2-----F1---
1. 2739 2738
2. 2733 2734
3. 2735 2738
4. 2739 2741
5. 2736 2738
6. 2712 2710
7. 2715 2715
8. 2748 2748
9. 2753 2753
10. 2724 2723
--------------------
Av.2733 Av. 2733
Sd. 13 Sd. 13
Es. 41 Es. 43

I was amazed with the above result! I didn't expect for a minute to have readings so close and often the same. Granted there would be maybe a few fps in it as the F1 was at 10 feet and the Magnetospeed at the muzzle.

I just thought it was interesting as people often say cheap chronographs aren't worth it and are often nowhere near the truth, at least my F1 in these light conditions on this day seemed pretty good! (Although all chronos need to be set up accurately and parallel to bullet flight.)

Anyway I'm delighted with the Magnetospeed and wont be getting any more error messages with bright sun, misalignment issues and can even go and fire a few shots into my garden at night after a reloading session with the V2 fitted and get good info even in the dark! I had quite a few dull afternoons this winter trying to get chrono speeds with the F1 and got mostly error messages or ridiculously low or high speeds because of lack of daylight.
 
The rounds I had were my standard loads that have always been velocity accurate through my chrono +/- 10fps. I didn't have the chrono with me as I thought I knew what the load was doing. Really glad we took the time to work through the errors. Just amazed at how cr4p my chrono is!

Al
Were you using the diffusers? Low readings on my F1 can also be caused whilst using in poor light conditions.
 
That is good news farmer, I have a f1 chrony and I thought mine was pretty accurate from calibres and loads ive tested, my mate has the same chrony, we have said we should put one in front the other and compare but we havent as yet, ive recently test a 120gr nbt with my 6.5 06, nosler data sez 52.5grs of imr 4350 should give 3235fps through 24 inch barrel, my load is 1gr down from max at 51.5grs of imr 4350 out og 26 inch barrel gave 3204 and 3215fps with 2 shots, am happy with fps figures
 
Were you using the diffusers? Low readings on my F1 can also be caused whilst using in poor light conditions.

The loads were pre-worked and not tested on the day, but I am really an4l over my loads and everything is weighed and measured to the last degree. I have always used the diffusers with my chrono as I have always assumed that they were needed.

I think that I will follow Barkingsnake's advice and run through a load of tests starting with the 22LR.

Al
 
...a load of tests starting with the 22LR.

My Chrony returned this:
22LR RWS Club
993
993.2
1007
1009
1024
1035
1006
995.1
993.8
MIN993
MAX1035
SPREAD42
AV VEL1006.23
SD14.9

Not sure if RWS Club is generally available but it runs a treat in my Ruger 10/22 semi-race gun.
 
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