Shot Marker Velocity For Load Development.

[JPB4BAMA]

Maybe I missed this after searching for similar information, so forgive me if that is the case and direct me to the correct place.
I recently recieved my shot marker with the hopes that I would be able to "back calculate" my muzzle velocity so as to do load development without the magnetospeed strapped on the barrel. What I have seed is that the shot marker velocity rather consistently results in a velocity at both 600 and 100 that when I use the berger calculator and the shooters calculator to reverse calculate my MV is about 130 fps slower that what I read on the magnetospeed. So.. I then had the chance to shoot with my magnetospeed, a Labradar and the Shot marker in tandem. Magnetospeed and Labradar agree within about 10 to 15 fps. This with the fact that my drop at 600 with an 88gr Hornady ELDM is also almost spot on to the MV from the magnetospeed and the Labradar.
So I contacted Adam ( who is great and customer response by the way) and he indicates that he has confidence in the downrange velocities IF my frame is flat and true and reasonable wind conditions. OK I buy that. He also stated that the published BC's area usually at 300 and that could be a factor. So today I shot against another shotmarker at a club match, and same thing, about 130 fps terminal at 600 than my load shows on the magnetospeed. so SM1 and SM2 seem to show the same thing on different frames of different sizes, But still my drop is pretty much spot on. I'm stumped or stupid, not sure which one.

223 AI 24.1gr Varget Hornady 88ELDM (G7 0.274 published) 50 Deg F, 30.01 at sea level.
Magnetospeed 2650 (sd 9)
Berger calculates terminal with 2650MV = 1747 with 4.27 MIL drop
SM2 reads 1645. Back calculating this should be a MV 2520 with 4.82 MIL drop.

Scope was dialed to 4.3 MIL and in the X or 10.

I would not trade the SM for anything, as it is spot on with respect to the impact points, just hoping that I could use it for Velocities without having to shoot a string with the Magnetospeed, and then another without it to see the group, as that thing hanging on the end does affect group size rather significantly at least in my case.

Any help or words of wisdom are appreciated.

JPB

 

[rhovee]

I have a Silver Mountain target and was hoping the same thing.
But after many shots I don’t trust the SD or FPS at the target. My LabRadar had an SD of 5.9. Silver Mountain target was SD 22.

 

[lawrence97]

Sounds like your problem is the magnetospeed! Sell it and purchase a Labradar.

The Shotmarker velocity is good to have but cannot be trusted to back calculate muzzle velocity as you have confirmed x 2. The Shotmarker velocity is a mess if you ever shoot in high winds…. If you want to track velocity without disturbing barrel harmonics look no further than the Labradar.

 

[VA_XTC_Shooter]

Sounds like your problem is the magnetospeed! Sell it and purchase a Labradar.

The Shotmarker velocity is good to have but cannot be trusted to back calculate muzzle velocity as you have confirmed x 2. The Shotmarker velocity is a mess if you ever shoot in high winds…. If you want to track velocity without disturbing barrel harmonics look no further than the Labradar.

How is the problem the magnetospeed? It was basically the same reading as the Labradar.

the issue is the discrepancy between shot marker down range and BOTH labradar and magnetospeed at muzzle.

 

[Twdmar]

Those microphones are what, 2 inches apart? How precise do you think that should be? At 600 yards, what is the angle the bullet is at as it crosses from one microphone to the next?
I don't know if the shotmarker can calculate the angle of bullet travel but I don't really think the shot marker is the only tool that should be used.
The lab radar is a good idea. I really like the E-targets for ladder testing. I shot highpower and the accuracy requirement is not as high as say, benchrest.
I shoot a ladder test at 600 and with only that one test, I can usually find a good load for 1k. Then if i really want, I can tweak seating depth etc. But usually it works quite well with minimal work.

 

[Dave M.]

How is the problem the magnetospeed? It was basically the same reading as the Labradar.

the issue is the discrepancy between shot marker down range and BOTH labradar and magnetospeed at muzzle.

Pretty sure the magnetospeed jab was sarcasm. I think he was just kidding.

 

[lawrence97]

How is the problem the magnetospeed? It was basically the same reading as the Labradar.

the issue is the discrepancy between shot marker down range and BOTH labradar and magnetospeed at muzzle.

JPB4BAMA posted this:
“hopes that I would be able to "back calculate" my muzzle velocity so as to do load development without the magnetospeed strapped on the barrel. “

Having something such as the magnetospeed strapped on the barrel can affect barrel harmonics. That’s why the original poster had hopes that the Shotmarker would be a solution that would allow back calculating muzzle velocity. Unfortunately the best option to calculate muzzle velocity is to measure velocity at the muzzle. The Shotmarker was not designed to replace a chronograph. It is an open microphone system with each microphone a few inches apart that can be negatively affected by high wind, bullet angle when passing through sensors, dependent on frame quality and stiffness, etc. What the Shotmarker does do well is beat having a camera system or having someone pull targets to verify shot placement.

As for the magnetospeed and Labradar, the Labradar wins as it does not affect barrel harmonics. Both units are accurate at providing muzzle velocity. I prefer to not have anything strapped to my barrel that could affect barrel harmonics when testing. Barrel harmonics is the reason tuners are used and the magneto acts like one when hanging on the barrel.

 

[JPB4BAMA]

JPB4BAMA posted this:
“hopes that I would be able to "back calculate" my muzzle velocity so as to do load development without the magnetospeed strapped on the barrel. “

Having something such as the magnetospeed strapped on the barrel can affect barrel harmonics. That’s why the original poster had hopes that the Shotmarker would be a solution that would allow back calculating muzzle velocity. Unfortunately the best option to calculate muzzle velocity is to measure velocity at the muzzle. The Shotmarker was not designed to replace a chronograph. It is an open microphone system with each microphone a few inches apart that can be negatively affected by high wind, bullet angle when passing through sensors, dependent on frame quality and stiffness, etc. What the Shotmarker does do well is beat having a camera system or having someone pull targets to verify shot placement.

As for the magnetospeed and Labradar, the Labradar wins as it does not affect barrel harmonics. Both units are accurate at providing muzzle velocity. I prefer to not have anything strapped to my barrel that could affect barrel harmonics when testing. Barrel harmonics is the reason tuners are used and the magneto acts like one when hanging on the barrel.

OH yes it most certainly does. Unfortunately I aint good enough to strap it in the exact same place every time, If I could I would. But you are spot on with my problem, and a LabRadar is in the plans. With that said, being an engineer myself albeit an old Metallurgist and not electrical type, the underlying explanation of WHY still plagues me. I was thinking along the lines of sensor distance, clock speed, and even shot placement, but with the same thing repeating on two differrent systems, (one on multiple sets of sensors) puzzles me. If it were sensor spacing and clock speed I would have thought that it would vary both high and low, but it is consistently low.
As for the SD's they track, but at different degrees. Higher on one end is aways higher on the other and vice versa, The absolute value I understand has 600 yds of environmental to contend with so the actual number does not really bother me.
THanks for the reply to all

 

[dellet]

If I read that correctly, you used the published BC instead of actual BC. If you still have the Lab Radar readings, calculate actual BC from the velocity readings captured in the first 100 yards.

Using the provided information 2650 MV, 1645 at 600 yards, calculates a true BC of .250 G7.

Using .250 as the BC in the calculator instead of .274 changed the MIL adjustment .2 from 4.4-4,6, and a terminal velocity difference of 90 fps. Using the info you posted. Guessing scope height and humidity.

If you have not done it, you might want to confirm you’re scope adjustment at 600 yards. Does 1 MIL adjustment move impact 1 MIL.

 

[Jeff Porter]

I would be curious how the LabRadar measured velo at 100 yards compares to the SM values. We make a lot of assumptions and calculations based on BC. Litz and Praslick did a series of podcasts about No BS BC and it was enlightening as to what happens in real time and across multiple shots all along the flight path of the bullet.
As I am typing this I see dellet has posted a similar post to where I was headed.


Given the potential errors in angle of shot wind at the target and other mentioned already in the SM I use it as a tool and make assumptions based on those values but always verify at distance and get real DOPE. I shoot mostly KD square range stuff so my requirement for accuracy is not as critical as others. YMMV.

 

[JimSC]

a comparison of 10 shots using Pro Chrono @ 12 feet from muzzle, Labradar ?? feet from muzzle, Shotmarker at 100 yards and Magnetospeed @ muzzle. The 1st shot on Magnetospeed was missed because I forgot to plug it in ...oops

 

[JimSC]

just out of curiosity how do you guys with Labradar verify that the LR is picking up the shot at the same place, shot to shot and session to session? Any changes in angle of the unit would certainly change the readings due to placement of the unit or vibration of the unit itself due to wind. In my opinion the most accurate readings would be from the magnetospeed since there is nothing that could change, shot to shot or session to session

 

[Kimber.204]

I recall @F Class John mentioning in one of his videos that he still used the labradar for velocities and didn't exactly trust the shot marker. It's still a great product, but it would need to be notably more expensive to be more accurate.

 

[SGK]

If you speak to Adam you will likely find it his view that the velocity measurement of the ShotMarker isn't accurate enough for load development where you are trying to use sample statistics to peek at the underlying behavior of load characteristics.

 

[BCBRAD]

Similar experience with Solo, velocity range wider than at the muzzle with a LabRadar.
Just an observation, load development is done at 100 yds and verified all the way out.

 

[Jeff Porter]

Still waiting for a labradar 100 yard velo compared to a SM or Solo open Mike unit at 100 yards.

My guess is the measured difference between the two at 100 will be a lot less than the back calculated versus measured at the muzzle. You are trusting a lot of variables in a ballistics program to be correct when you back calculate. Altitude density BC air temp and humidity …. If you are not spot on there will be an error introduced. Most are not huge errors but they are baked in the cake if you use default settings. GIGO. (Garbage in garbage out. )

 

[Tod Hendricks]

Put your labradar down range, you have to get the bullet pretty close to trigger it, but it works, and you need to trust your equipment.

 

[Ned Ludd]

The velocity data from a ShotMarker system requires a healthy dose of caution. Sometimes it matches up well with predicted velocity decrease at a given distance. Sometimes it does not. I would put my money on the velocity data generated at the muzzle via a reliable chronograph such as you have been doing, rather than use the ShotMarker velocity data. You can then compare the necessary elevation setting at a particular distance to the predicted drop rather than using the ShotMarker velocity at the target face.

 

[Jeff Porter]

So what I hear everyone saying is you can’t back calculate a useful MV from a shotmarker…….but you should take a measured MV then tweak the BC in the ballistics calculator to match the observed elevation changes to true your dope. If your scope is tracking correctly and you know for sure it is MOA and not inches per 100 yards ( yes, the .047” will show up at longer range ) Doesn’t seem like much of a difference.

You take an out put ( velocity from labradar or magneto speed or the shotmarker ) and play with the inputs in the ballistic calculator until elevation predictions matches what you are actually shooting at distance.

I am not arguing that labradar velos are not more accurate measurements than the SM. Just saying that the difference in SM velos back calculated to MV at distance may not be totally due to the SM. BC is rarely what you enter and varies from shot to shot and during the flight of each shot as velocity bleeds off. Unless you are using the Labradar ability to track velo out more than 50 yards and determine a true BC, just using it as a chronograph still leaves you tweaking data. What the guys at Applied Ballistics do to true your dope up involves a lot more than a single velo data point.