Please help explain

[lrgrendel]

I shot this morning. All within an hour and a half.
Central Florida. Approx 70 deg.

All 33 rounds were loaded at the same time prior to shooting and have the same powder charge.

I waited approx 5 minutes between groups for barrel to cool.

If you notice the average FPS climbed approx 50 FPS between the first 3 groups and the second 3 groups.

I shot the first 3 groups at 200 yds and the second 3 at 300 yds.

The exact same thing happened last week.
I hope the posted photo can be seen by everyone.

BTW Slight primer flattening, no other pressure signs.

Thanks.

[explorecaves]

Freshly scrubbed barrel to begin with or did you also shoot fouler shots before taking readings?

[bwaites]

I shot this morning. All within an hour and a half.
Central Florida. Approx 70 deg.

All 33 rounds were loaded at the same time prior to shooting and have the same powder charge.

I waited approx 5 minutes between groups for barrel to cool.

If you notice the average FPS climbed approx 50 FPS between the first 3 groups and the second 3 groups.

I shot the first 3 groups at 200 yds and the second 3 at 300 yds.

The exact same thing happened last week.
I hope the posted photo can be seen by everyone.

BTW Slight primer flattening, no other pressure signs.

Thanks.

Most likely explanation is your chrono, not your load. 1 hour means significant difference in height of sun in the sky and chronographs are notoriously dependent on exactly the same lighting for consistentcy.

[lrgrendel]

Yes the barrel was just cleaned but last week it was not. I had fowlers to shoot but did not shoot them as fowlers. That is why there is one group of 8!!
The 6 groups in the photo is the order in which they were shot. The first group was pretty consistent regarding velocity but the first 2 shots were well "off " I guess to not shooting fowlers.

Thanks

[stevegun 1]

Most likely explanation is your chrono, not your load. 1 hour means significant difference in height of sun in the sky and chronographs are notoriously dependent on exactly the same lighting for consistentcy.

++1, What Bill wrote, who's chrono are you using?

[lrgrendel]

++1, What Bill wrote, who's chrono are you using?

It is a Chrony Beta Master

[VASCAR2]

The Chronograph is a time distance computer with a very precise clock with electronic eye for start and stop. The chronograph will produce the most consistent results on overcasts days or in artificial lighting. It also requires a straight flight path across the start and stop sensor. As the sun moves in the horizon the distance the sensor can see the bullet shadow can change.

The chronograph is basically a speed timer on the same principal as VASCAR V-Visual A-Average S-Speed C-Computer A-And R-Recorder. The distance divided by time equals speed. As the sun moves and the distance viewed by the sensor changes so will the speeds. This slight change might not be obvious because of the normal variation in powder charge, primer or other factors affecting true velocity. I've never looked at the manual on a optical chronograph to see if they specify a specification for accuracy + or - minus so many FPS.

I know radar is used by ammunition manufactures along with printed circuit start and stop boards to get more accurate readings on velocity to help determine ballistic coefficients.

The magneto speed timers on the market may have an edge since they don't use the shadow cast by the passing bullet. With out doing the math I'd be surprised by more than 1-2% change on velocity readings due to the movement of the sun. I know from personal experience the chronograph will quit reading velocity if the sun is in the wrong position in relation to the sensor.

[lrgrendel]

The Chronograph is a time distance computer with a very precise clock with electronic eye for start and stop. The chronograph will produce the most consistent results on overcasts days or in artificial lighting. It also requires a straight flight path across the start and stop sensor. As the sun moves in the horizon the distance the sensor can see the bullet shadow can change.

The chronograph is basically a speed timer on the same principal as VASCAR V-Visual A-Average S-Speed C-Computer A-And R-Recorder. The distance divided by time equals speed. As the sun moves and the distance viewed by the sensor changes so will the speeds. This slight change might not be obvious because of the normal variation in powder charge, primer or other factors affecting true velocity. I've never looked at the manual on a optical chronograph to see if they specify a specification for accuracy + or - minus so many FPS.

I know radar is used by ammunition manufactures along with printed circuit start and stop boards to get more accurate readings on velocity to help determine ballistic coefficients.

The magneto speed timers on the market may have an edge since they don't use the shadow cast by the passing bullet. With out doing the math I'd be surprised by more than 1-2% change on velocity readings due to the movement of the sun. I know from personal experience the chronograph will quit reading velocity if the sun is in the wrong position in relation to the sensor.

Vassar2

That is very interesting reading thanks.

As a buddy also pointed out who was with me, I moved the chronograph about 5 or 6 ft to the right when I changed from 200 to 300 yds.

Your estimation also looks spot on as the 50 FPS equates to about 2%.

I need something more accurate!!

[stokesrj]

I have a Magnetospeed you are welcome to try out if you like. I'm in the Tampa Bay area but visit CFRP, Malabar, and Manatee often.
Bob

[cory]

I have a Magnetospeed you are welcome to try out if you like. I'm in the Tampa Bay area but visit CFRP, Malabar, and Manatee often.
Bob

Have you seen any decrease of accuracy or a false accuracy node using the Magnetospeed as has been reported with non Bull barrels.

[lrgrendel]

I have a Magnetospeed you are welcome to try out if you like. I'm in the Tampa Bay area but visit CFRP, Malabar, and Manatee often.
Bob

Stokesrj

I live North of Orlando but I appreciate the offer. Thanks.

[Onewolf]

Do you shoot at the Geneva range or the Volusia county range?

[waveslayer]

Have you seen any decrease of accuracy or a false accuracy node using the Magnetospeed as has been reported with non Bull barrels.

Yes and Yes! I experienced major POI shift. I made the mistake of taking the Magnetospeed off and on to use it on other rifles to test velocity while the other guns were cooling down. big mistake, my POI on my 308, which is a tack driver, was almost 6 " off!

so lesson learned: leave it on the gun and don't mess with it if you are testing loads.

Otherwise I love it over my normal chrony, I get better velocity readings. never have to worry about lighting again. I used in an indoor range and it was awesome.

[Klem]

Talking about potential faults of the Chrony which opens up to read. If the two halves of the Chrony are not exactly opened hard against the hinge stops the distance between the two sensors is shorter than calibrated. Even a tiny bend in the hinge translates to 50fps.

The angle to the bore axis is the same. The slightest angle means the distance between sensors is shorter to the bore axis. I use a level bubble every time I set it up so it's parallel to the ground. It may not be exactly parallel to the bore axis but it's pretty close and at least consistent every time it is used.

Something like this that's small enough to sit inside the Chrony.

[stokesrj]

Have you seen any decrease of accuracy or a false accuracy node using the Magnetospeed as has been reported with non Bull barrels.

Yes, with thin hunting rifle barrels it typically deflects the bullet away from the blade it passes over and the node will definitely change. On my bull barreled panda, it doesn't care one way or the other, it shoots bug holes with the magneto speed on or off and the POI doesn't change.
Bob