Interesting chronograph results

[drumcorpschamp]

All,

I am going through the process of load development for my .260 Rem. and am using a Competition Electronics Pro Chrono to clock my loads. The interesting thing (to me) are the repetitive velocities that the chrono displays. Anybody have similar results with this particular unit, or units from other manufacturers?

3/8/12 Partly cloudy, temp. 50's, optimum charge weight testing, .4 gr. increments:
1) 2801, 2818, 2801
2) 2830, 2849, 2836
3) 2836, 2855, 2842
4) 2879, 2855, 2892
5) 2911, 2892, 2898
6) 2886, 2892, 2879

Different powder:
1) 2704, 2732, 2732
2) 2766, 2732, 2749
3) 2766, 2760, 2772
4) 2783, 2824, 2824
5) 2830, 2818, 2818
6) 2855, 2867, 2842
7) 2886, 2886, 2873

I had similar results on days where the sky was overcast, bright sun and temperatures from mid 40's through 70 deg. F and I won't bore you with all of the numbers. The common indicator that I am seeing is that numbers are exactly duplicated throughout each session.

The curved plastic screen were in place during all shooting sessions and the instrument was placed at 15 feet from the muzzle. Angle of the bore and the instrument were both level as bench and target height (100 yds.) are virtually the same.

Any thoughts, suggestions or insight would be most welcome?

Thanks,
Jerry Ware

 

[CaptainMal]

I also now use the same chronograph. Also get the same "dup" reading at times.

Most times I DO NOT get many "dup" readings. Cannot figure it out, have never seen a pattern and I now think it's just something that happens. If all things were perfect you would expect each shot to be exactly the same. That's not going to happen and when it does, we complain.

Like you, I have no answers, only questions.

That plastic sheet over the readout damages easily. I used Blackhorn 209 in a muzzeloader to burn a nice hole into that sheet even after I covered it with a baggie so it would not happen.

 

[nra-for-life]

i see you do get some duplicates...ive never had that problem so i don't know what to say....it is interesting how your numbers climb though. how long are you waiting in between shots??? do you see your poi start to shift up?

 

[drumcorpschamp]

i see you do get some duplicates...ive never had that problem so i don't know what to say....it is interesting how your numbers climb though. how long are you waiting in between shots??? do you see your poi start to shift up?

The velocity numbers increase string to string as the powder charges were increased by .4 gr. per string. It took a couple hours to fire these strings as I was taking things slow and waiting out the wind gusts. The barrel only got a little warm through the session. Negligible POI shifts in groups.

Jerry

Jerry

 

[drumcorpschamp]

Dave,

I was seeing that with the numbers and not really knowing what to make of it other than whatever number I see, just assume the "real" velocity would be somewhere in the +/- 3 fps range.

At this point, I just wish I could get my gun handling skills to be more true than my chrono results. But that's another struggle altogether!

Jerry

 

[Outrider27]

I shoot the same chronograph and based on my observations, I think that Dave hit the answer in Post #3. Note that I have had occasion to do considerable work with rimfire ammo and at those velocities, you don't see that type of pattern, reinforcing the probability that it is caused by resolution capabilities.

 

[amlevin]

I had a similar issue with an older chronograph that was real "light sensitive". Readings changed as the sun moved and shadows on the ground changed as well.

I got a new unit with IR sensors and don't have the problem anymore. Apparently, since this unit provides its own light source it senses the bullets more uniformly for start/stop signals. Sunlight can be it's own variable.