Extreme ES caused by barrel?

[jdavistx]

Really dumb question. Please don't take offense. Are you mixing the Nosler and Remington Brass? If so, that's a huge no-no and would explain everything.

Also, I am a huge fan of the LabRadar Chronograph. It's a whole new paradigm. Beg, buy, or borrow one to compare against your chrono. I note that your other chrono testing is on larger diameter bullets. Generally, I would say that it's normal to see this. Faster and smaller is harder to see for a lot of reasons. That's true of the LabRadar too, but if you get data, it's almost always good data which is not true of other chronographs. Another poster said, chronographs lie, paper doesn't. I would modify that to say that most chronographs lie, Labradar and paper don't. Anyway, try it.

Lab radar is the best. If you can spend 8 grand on a gun, you can also buy Lab Radar.

 

[longestrange]

Optical chrony's will error out if too close to the muzzle - no reading. Rifle rounds require more distance than pistol rounds. Whether this is due to the muzzle blast or shockwave shadows or whatever I don't know. It is possible that this effect is taking place more subtly at marginal distances, causing the crony to trigger prematurely/erratically depending on individual trajectories over the sensors. You may want to move it another 10 or 15 feet out to see if that helps. This might also explain somewhat the sunny/cloudy differences, as a shockwave shadow would have more effect on a sunny day. The screens do seem to help with this while they survive
I can't test this theory at the moment but it would be interesting if anybody else could have a look. Like my old prof used to say - 'One good test is worth a thousand expert opinions'.

 

[Susquatch]

Optical chrony's will error out if too close to the muzzle - no reading. Rifle rounds require more distance than pistol rounds. Whether this is due to the muzzle blast or shockwave shadows or whatever I don't know. It is possible that this effect is taking place more subtly at marginal distances, causing the crony to trigger prematurely/erratically depending on individual trajectories over the sensors. You may want to move it another 10 or 15 feet out to see if that helps. This might also explain somewhat the sunny/cloudy differences, as a shockwave shadow would have more effect on a sunny day. The screens do seem to help with this while they survive
I can't test this theory at the moment but it would be interesting if anybody else could have a look. Like my old prof used to say - 'One good test is worth a thousand expert opinions'.

Yes, for reasons too lengthy to explain, I have a very keen interest in all things chronograph. I have tested this problem at length under lab conditions. This weakness of optical chronograph is yet another reason that I am so impressed with the LabRadar.

My assessment revealed multiple sources of error when the screens are too close to the muzzle.

The first is movement of the first screen itself and when they are close coupled on a fixed space bar (like the CED) there can be movement in both screens.

The second is hysteresis in that movement. They don't always settle back the same way after each shot.

The third does appear to be shock wave errors - not from the bullet itself, but rather from the muzzle blast of compressed supersonic gas that leaves the muzzle before the bullet does.

The fourth is very easy to manage, but it always amazes me that so many shooters don't know about it or care. That is returning the rifle to the exact same position between shots.

All of these errors can add up and/or cancel out.

In all cases, the main problem goes away with adequate distance from the muzzle. Before I got my Labradar, I used to put my chronograph screens 25 ft ahead of the muzzle. It is easy to back calculate the muzzle velocity at this distance.

Of course, the Labradar is not prone to these errors. What a terrific advancement!

 

[longestrange]

In all cases, the main problem goes away with adequate distance from the muzzle. Before I got my Labradar, I used to put my chronograph screens 25 ft ahead of the muzzle. It is easy to back calculate the muzzle velocity at this distance.

Of course, the Labradar is not prone to these errors. What a terrific advancement!

So for us landlubbers an optical chrony might be plenty good at 25' for rifle rounds, and 25' might also solve the OP's issues.
Of course this brings up the possibility of a head-to-head comparison of optical vs. radar vs. whatever if it is possible to run them simultaneously. That would be very interesting, and could save almost $600 depending on the accuracy desired.

 

[Susquatch]

So for us landlubbers an optical chrony might be plenty good at 25' for rifle rounds, and 25' might also solve the OP's issues.
Of course this brings up the possibility of a head-to-head comparison of optical vs. radar vs. whatever if it is possible to run them simultaneously. That would be very interesting, and could save almost $600 depending on the accuracy desired.

It's certainly possible. In fact, other than the layered film type used in the 60s and 70s, you could compare any set of chronographs this way.

But quite frankly, I lost all interest in all my spaced screen chronographs when I got my LabRadar. Any comparison would only prove how inferior the old ones are and how much money and effort I wasted on them in years gone by. Its sort of like doing a side-by-side comparison of a slide ruler to a scientific calculator to a modern computer. I still have my slide ruler someplace but I NEVER use it anymore. It would be pointless. I guess I feel exactly like that with Chronographs. The LabRadar is a whole new paradigm shift in technology. I still have my old chronographs, but they are only fond memories now.

I did write a review of the technology for the LabRadar vs Screen Chronographs when the LabRadar first appeared. I wrote it for the purpose of helping others understand why Doppler Radar was so superior to other methods for velocity measurement. But I never posted it and I'm not even sure I could find it again. Maybe I'll have a look when I get the chance.