Thread: What's the Deal?

What weight bullet R93?

Originally Posted by Wirehunt

What weight bullet R93?

140 Amax



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Originally Posted by Normie

Not sure what the book speed is but I'd imagine I'm slower than it should be. The day was perfect for the chrony too. Nice clear day 24 degrees or so in the middle of a paddock.

The powder used is ADI 2209 so fairly temp stable.

If it helps my load is
Lapua .260 Brass
140gr A-Max
42gr AR2209
CCI BR primer

22" MAB 1:8 barrel

Bullets on target don't lie chroro's do. Some of the worst readings Iv had from a shooting chrony have been in full sun. I have a hunch that pointy high bc bullets are harder for the sensors to read accurately as well.

Originally Posted by sneeze

Bullets on target don't lie chroro's do. Some of the worst readings Iv had from a shooting chrony have been in full sun. I have a hunch that pointy high bc bullets are harder for the sensors to read accurately as well.

Too much light is as bad as not enough, alright. Had some ridiculous readings as well.
I haven't tried it but know some people use a vivid to blacken their projectiles so they are easier for the chrony to pick up on bright days. May be worth a go.



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Originally Posted by R93

Too much light is as bad as not enough, alright. Had some ridiculous readings as well.
I haven't tried it but know some people use a vivid to blacken their projectiles so they are easier for the chrony to pick up on bright days. May be worth a go.
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Yes might help but you just cant trust the shooting chronys. The sensors are very close together so any error is significant and speed readings will change with the light .As has been said many times you need to validate at range whatever machine you use. The CED II with IR screens is the most reliable at a reasonable price but even that works better in a box that cuts out the sun.

Originally Posted by sneeze

The CED II with IR screens is the most reliable at a reasonable price but even that works better in a box that cuts out the sun.

What do you mean by that mate? I have tested some of mine in the dark. Some times faster than my daylight readings and sometimes slower but not by much, over different strings (Usually within 50fps), using the same load.
I would have thought with the ir screens you would get a more accurate and consistent reading at night? Temp?

Yes dark is good with the ir screens but if in the day time the ambient light still seems to have the ability to interfere and bright sun even more so. Worst is when the sun can hit the sensors direct. Could go some way to explaining the variations you are seeing along with powder/barrel temp maybe. We can put it to the test if you make it to the farm for a few days.

I watched my f1 jump 150 fps as a shadow moved over it, low teck i know but i use it comparatively if at all i e shoot a known load first and add or subtract the variation from actual validated speed.

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Originally Posted by sneeze

Yes dark is good with the ir screens but if in the day time the ambient light still seems to have the ability to interfere and bright sun even more so. Worst is when the sun can hit the sensors direct. Could go some way to explaining the variations you are seeing along with powder/barrel temp maybe. We can put it to the test if you make it to the farm for a few days.

Yep, sounds good. I will bring mine up and see if there is any major difference in readings between the 2.

Originally Posted by veitnamcam

I watched my f1 jump 150 fps as a shadow moved over it, low teck i know but i use it comparatively if at all i e shoot a known load first and add or subtract the variation from actual validated speed.

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Thats it, they serve a purpose but I think to many people put far to much faith in the little numbers that appear on the screen, it seems to have a sort of hypnotic property

I always use Brian Litz Bc's. I'd key in what he said for the projectile, key in the atmosphere, use your chrony reading, shoot at range, adjust accordingly then massage the speed till it matches the actual drop....like you have. Even with an Oehler chrony, keying in all the atmospheric conditions etc I can still be out in the drop department.
Chronograph's are at best to give you something to measure ES spread....don't take the actual speed as gospel.

P.S - on a side note the Oehler will almost never give a reading for a Nosler ballistic tip.....Weird! No issue with any other bullet

I believe that bullets CAN lie, in the sense that they often lead to wrong assumptions.

Checklist if elevation to hit centre consistently doesn't match chart:
-shooter error
-poor zero
-incorrect range
-mixed unit for range/chart
-shooter error
-incorrect data entered in calculator to generate chart (BC, speed, height above bore, atmospherics, zero range)
-chronograph incorrect
-scope adjustment not accurate
-angle not accounted for
-incorrect BC
-inconsistent ammunition
-compounding effects of several of the above

A log is important.

Originally Posted by Normie

From 9 measured shots through the chrony

My guess. Can't argue with physics, the math is well known, bullet is well documented, the weather isn't a big enough factor so that leaves the measurement?

What zero range for the rifle? And what zero range entered in the app? Because I'm waiting for a plane in Singapore and have had 3 very large black coffees I have had a play with JBM.

With 2644fps and 100m actual rifle zero/100m zero entered in program the 500m elevation is 3.8mil, 650m is 5.9mil (ie the ~corrections that you required to hit)

With 2644fps and 100m actual rifle zero/200m zero entered in program the 500m elevation is 3.1mil, 650m is 5.2mil (ie the 500m ~correction that did not hit, we had no information supplied about misses at 650m)

2500fps is super slow for that powder/charge/bullet/case.

A theory: your rifle is zeroed at 100 meters but the program was set for a 200 meter zero. I can believe an easily overlooked data input error, they happen regularly.


Edit: I think I accidentally did all that with JBM set to G6 not G7 but that just kinda proves my point of how easy it is to miss one little input in a program, doubly so outdoors on a phone etc

Originally Posted by Normie

Not sure what the book speed is but I'd imagine I'm slower than it should be. The day was perfect for the chrony too. Nice clear day 24 degrees or so in the middle of a paddock.

The powder used is ADI 2209 so fairly temp stable.

If it helps my load is
Lapua .260 Brass
140gr A-Max
42gr AR2209
CCI BR primer

22" MAB 1:8 barrel

ADI book speed is 2675 in a 24" the slight lose in speed would be equal to your 22" so your chrony speed is pretty spot on.