Explanation anyone?

[RCMSTER]

So my question is this. Shot this 5 shot group tonight out of my 6.5-06 that I just bought off of Gunbroker. Of them 5 shots, the first 4 shots averaged 2898 fps, while the last shot plummeted to 2708 fps. I loaded up 3 more rounds with an increase of .5 grains of Supreme 780 to 49.5 grains. Them 3 shots averaged 2740 fps. I'm baffled to this, but my first thought is that I need a new battery in my chrono. My other question would the warm barrel cause this much velocity drop. Temp outside is 77 degrees.
In regards to the 2nd pic of the primers, what's ya'lls thoughts? To me they look fine yet, as in no high pressure.

 

[ShtrRdy]

What kind of chrono are you using?

If it's an optical type was the chrono in the shade of a tree or were there broken clouds floating over?

 

[RCMSTER]

Shooting Chrony, Alpha model. No shade. Solid sun.

 

[MNbogboy]

Nice shooting, my guess that it's the chrony.

The optical chronos are dependent on even light to be consistent. Bright sunlight seems to be very erratic as shadows over the sunshade change as the sun moves.
Bright sunny days have shown the most inconsistency in my many years shooting over optical chronos. Early morning while mine was in the shade was ok. High noon was bad as well as late in the day. Snow crystals blowing out of trees will give them fits. The light level above each trigger will determine when the comparator circuits will trigger the on/off of the timing circuit.

Overcast days have always shown to be more consistent. I had fashioned "light boxes" to provide more even lighting.
Have since graduated to the magneto speed and reliability is much better.

My bet is your load is great and the target shows it. As far as barrel temp, I usually see lower velocities when the barrel is cold and the speed up with temp.

Try the same load again with overcast conditions and the ES/SD will most likely be much smaller.

 

[jd5521]

It's your chronograph

 

[26Reload]

Yep...i go with the chrono...as mine gave me some funky speeds a few weeks ago.....they were very uniform speeds but about 100fps slower(brand new battery).....
Firs time I ever had that happen...i built a cover over the top of the chrono..helped..but needed to be a darker grey color...it was white....to much reflection.....

 

[Tiny Tim]

Change batteries. And as others have pointed out, make certain your lighting is consistent. If its rapidly changing like early or late in the day, it will affect your readings. Also, if not level, it will read fast or slow depending on angle in relation to bore.

 

[RCMSTER]

It was definitely late in the day, about 6:30 PM. Not the best time of day for checking velocity, I assume. That's at least an easy fix. Thanks.

 

[26Reload]

I also had the chrono slip out of level....but it didn't change speeds as much a lighting affected it....

 

[PApa Black]

Nice shooting, my guess that it's the chrony.

The optical chronos are dependent on even light to be consistent. Bright sunlight seems to be very erratic as shadows over the sunshade change as the sun moves.
Bright sunny days have shown the most inconsistency in my many years shooting over optical chronos. Early morning while mine was in the shade was ok. High noon was bad as well as late in the day. Snow crystals blowing out of trees will give them fits. The light level above each trigger will determine when the comparator circuits will trigger the on/off of the timing circuit.

Overcast days have always shown to be more consistent. I had fashioned "light boxes" to provide more even lighting.
Have since graduated to the magneto speed and reliability is much better.

My bet is your load is great and the target shows it. As far as barrel temp, I usually see lower velocities when the barrel is cold and the speed up with temp.

Try the same load again with overcast conditions and the ES/SD will most likely be much smaller.

I have the same chrono and had the same problem. Installed the shields and that solved the problem.

 

[RCMSTER]

Guess I better put them on, and see what happens. Thanks for the heads up!

 

[oneeyejohn]

I see you are using .270 cases for your 6.5-06. I found that 25-06 cases work better, all you need to do is run the necks through your die and expand them .013 and go. The necks are not as thick as down sizing .270 or 30-06 case necks. You will not have a problem with donuts at the base of the neck with the 25-06 case..

 

[RCMSTER]

I see you are using .270 cases for your 6.5-06. I found that 25-06 cases work better, all you need to do is run the necks through your die and expand them .013 and go. The necks are not as thick as down sizing .270 or 30-06 case necks. You will not have a problem with donuts at the base of the neck with the 25-06 case..

I understand what you're saying, but I also have 2 25-06's, and I'm afraid that I'd manage to get them mixed up somewhere along the line, and I don't think that would end very well.

 

[Farmerboy78]

Man, I've seen optical chrono's give different speeds, depending on how high and if directly over center of the chrony. You really need to use someone's magnetospeed or lab radar. I use 30-06 brass for my 6.5-06. If you can find it, re25, h1000, and definitely re26 will probably work better.