Verifying a chronograph

[Elite]

Wondering if anyone has a way to verify a chronograph? My new rifle seems to shoot fast? Faster then the factory box lists for FPS and my hand load are fast for what the book says. It has a 22” proof research barrel. All the reloading books use a 24” so I have a hard time believing it is faster


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[A382DWDZQ]

Use multiple chronographs, or use a load & rifle combo that is known & stable.

 

[Rich M]

I have blue box federal ammo that is basically exactly whats written on the box. It also shoots and inch. I use it for qaqc w reloads.

 

[Tmac]

Sight in dead on at 100 yards. Use your chrono velocity in an app to determine drop at longer range. Shoot and compare. Truing your chrono I guess one could say. If drop is off, work back in the app to a velocity that matches the drop.

 

[BjornF16]

Sight in dead on at 100 yards. Use your chrono velocity in an app to determine drop at longer range. Shoot and compare. Truing your chrono I guess one could say. If drop is off, work back in the app to a velocity that matches the drop.

The bullet doesn't lie

 

[wind gypsy]

Sight in dead on at 100 yards. Use your chrono velocity in an app to determine drop at longer range. Shoot and compare. Truing your chrono I guess one could say. If drop is off, work back in the app to a velocity that matches the drop.

Might just be wanting a sanity check on new combos? I know I use a chrono as another means for real world pressure analysis too. For example I can load a 6.5x47 lapua case hot as hell with a thicker primer and not have much for pressure signs but my chrono would let me know if I’m I’m pushing a bullet faster than that little case has business doing.

The opposite can be true as well. If I’m getting lower speeds due to a slower lot of powder or maybe a barrel that doesn’t build pressure as fast, the velocity makes me more comfortable loading charges that might normally be questionable if I’m not seeing pressure signs.

 

[Dos Perros]

The bullet doesn't lie

This requires one to assume the published BC is correct?

 

[Tmac]

This requires one to assume the published BC is correct?

In the OP’s example, yes, one is pretty much assuming all other data, including bc & environmentals are correct. In the real world there are often small errors in multiple data points, noise if you will, sometime they offset, sometimes not.

 

[Wrench]

Complete a tall target test.

Zero at 100yds.

Shoot 300-600 and record corrections.

Input actual point of impact to any ballistics solver for corrected mv.

ALL OF THIS assumes you did the tall target test AND have a correct bc.

 

[Wrench]

Ps, you can do the above without ever touching a chronograph. You wont get es numbers.....but you'll get no BS impact corrections.

 

[Dos Perros]

@Wrench but then you'd have to correct for environmentals that have a delta from your baseline when actually hunting? I guess that would be the case if you had a chrono you trusted anway.

 

[35WhelenAI]

Wondering if anyone has a way to verify a chronograph? My new rifle seems to shoot fast? Faster then the factory box lists for FPS and my hand load are fast for what the book says. It has a 22” proof research barrel. All the reloading books use a 24” so I have a hard time believing it is faster


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Has the chronograph given results you would expect with other rifles and factory/handloads, as was brought up in post #2.

What is the differential between factory advertised velocity and your instrumental velocity, the differential between book velocity and what your hand loads achieve?

How do those stack up against each other, before you start shooting at a quarter mile and longer to check drops.

I have a Pro Chrono I've used for decades, also picked up a Magnetospeed in the last year. Given the Magnetospeed reads at the muzzle and the ProChrono reads 15-20 feet down range the difference basically matches the few FPS drop you would expect in 15-20 feet.

 

[Wrench]

@Wrench but then you'd have to correct for environmentals that have a delta from your baseline when actually hunting? I guess that would be the case if you had a chrono you trusted anway.

Wind speed and direction will be the biggest headache. Temperature is a variable that changes mv more than drag in most cases.

 

[Elite]

Thanks for the suggestions everyone. I have the pro chrono dlx. I tried running the sun covers even if it is cloudy and it seems to be a more realistic number but struggling with high ES now


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[Wrench]

Don't be afraid to shoot it at distance. There's a lot of guns that show higher spreads but print good groups.

 

[Elite]

Don't be afraid to shoot it at distance. There's a lot of guns that show higher spreads but print good groups.

My groups are currently .469” savage ultralight. 200grn eldx at 2648fps for the average


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[Elite]

My groups are currently .469” savage ultralight. 200grn eldx at 2648fps for the average


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That group was at 100 yards. Still need to get to the long range and test


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[Wrench]

Exactly. Stretch it out as far as you can and see what happens...you may be surprised.

 

[35WhelenAI]

To be clear, I wasn't trying to naysay on shooting at longer range. I was saying there's a bit more low hanging fruit that could help with an explanation and if there is no evidence from those things, then long range shooting is a good option.

 

[RS_Non-Res]

See Appendix B of this (or similar) document.
https://oehler-research.com/wp-content/uploads/2017/11/M36-Instructions.pdf

TLDR: If your optical chrono is properly aligned with the projectile trajectory, it's results are probably correct at it's location, except for grossly/obviously erroneous results.

Verification Process:
1) Use electronics voodoo tool to verify electronic clock is running at 66 Mhz, and
2) confirm (measure) that the distance between projectile triggers of the clock are the same as what the algorithms assume.

"Such counting and computations [as used in the Oehler chronograph] are commonplace and are normally subject to gross failures but not small errors." Clock may have 0.25% (1/4-%) error limited by the electronics.

The chrono should be aligned with the projectile path. 8* off can cause 1% error in trajectory distance and measured speed.

"The digital counting and computation is assumed to be correct. No calibration is required or suggested. If verification is required, we suggest use of the Oehler Model 76 firing simulator as a source of trigger pulses at known time intervals.

"The spacing between projectile sensors must be accurately determined during the operation and use of the system. Appropriate calibration and use of measurement devices is assumed."