Labradar speeds.?

[comagutsa]

Just a quick one
I have been load testing my new 6BRX and my labradar is giving me 2 different speeds for the same load on different days and it's done it a few times now
Eg 32.4gr or 2208/varget and 107gr Smk I get 2920fps one shoot. I then set up again another day and I get 2960fps. Set up another day and its back down to 2920fps.. Go home load up again and back to range a few hours later and I'm getting 2960fps.. Its done it a few times now and they are the same speeds just approx 40fps different?
All loaded with fx-120i scales
I set up the radar as close to the same spots every time. Anyone else had this
Cheers

 

[varget204]

Where Temp/weather conditions the same each day ?

 

[Willie]

Only thing that comes to mind is temperature or new brass vs fully formed brass. Or neck tension variance due to number of firings.

At least the differences are constant.

 

[ShootDots]

I have a very weird / odd story about Lab Radars. When I was testing my .300WSM I had MY Lab and John Farraggio (aka Cognac Jack on here) has his. We positioned them on either side of my barrel at nearly identical positions. His Lab read about 40 feet per second faster than mine. Then from time to time they were within a foot or two! How do you explain that one? The ONLY explanation I can come up with for these aberrations is, is that from time to time the Lab Radar "picks up" the bullet at different distances. The further away it picks it up, the slower it will read.. I know of no other explanation(s)...

 

[Elwood]

Just a quick one
I have been load testing my new 6BRX and my labradar is giving me 2 different speeds for the same load on different days and it's done it a few times now
Eg 32.4gr or 2208/varget and 107gr Smk I get 2920fps one shoot. I then set up again another day and I get 2960fps. Set up another day and its back down to 2920fps.. Go home load up again and back to range a few hours later and I'm getting 2960fps.. Its done it a few times now and they are the same speeds just approx 40fps different?
All loaded with fx-120i scales
I set up the radar as close to the same spots every time. Anyone else had this
Cheers

You're not alone, I have experienced this as well, as have others.

 

[Ballisticboy]

I have a very weird / odd story about Lab Radars. When I was testing my .300WSM I had MY Lab and John Farraggio (aka Cognac Jack on here) has his. We positioned them on either side of my barrel at nearly identical positions. His Lab read about 40 feet per second faster than mine. Then from time to time they were within a foot or two! How do you explain that one? The ONLY explanation I can come up with for these aberrations is, is that from time to time the Lab Radar "picks up" the bullet at different distances. The further away it picks it up, the slower it will read.. I know of no other explanation(s)...

The use of multiple muzzle velocity radars is common practice for artillery range and accuracy firing trials. When I was carrying out drag tests on small arms bullets we always insisted on using two muzzle velocity radars rather than the one the range was used to using. It is important that the two radars are using different signals to measure the velocity as if they are using the same signal they can intefere with each other. The range crew were very surprised at the difficulty in making to two radars agree with each other to the less than 1 metre/second we were demanding. Minute changes in the radar position or angle could produce large changes in the difference between the two measured muzzle velocities.
Neither radar was a LabRadar but they were fixed head doppler radars working on the same principles, just a lot more powerful and expensive. One thing we could do with these radars was to look at the raw data. There were distinct differences in the amount of data each radar collected depending on the accuracy with which the radar was set up relative to the gun. The amount of data had a large effect on the curve fit used by the radar to derive the muzzle velocity.
Of course, anyone using just one radar set would be completely unaware of the possible errors in the velocity readings due to small changes in the position or direction of the radar settings.

 

[DBLNUT]

My Magnetospeed does the same thing.........

 

[comagutsa]

Sweet sounds like a few people have had this..
Brass had been fire formed and only had 1 or 2 firings after being fire formed but speeds had the slow and fast speed difference on 1 firing and 2nd firing. It didn't matter..
Temperature of day was about 10 degrees C max but some where done at same temp a few days apart in the morning and had the slow and fast speeds then.
Just one of those things I'd say
Cheers

 

[PatMiles]

Dial up the folks at LR and pose the question to them?

 

[Jeff A]

I would be very interested to know about two settings on the LabRadar units used in this test. The first one would be the Projectile Offset setting of each unit and the other thing is what transmitter channel setting was on each of the units.

 

[mensajd]

The Labradar v0 would seem to be an extrapolated number (since the bullet is initially outside the radar beam) so if the unit picks up the bullet at different distances, presumably the error term would be larger for bullets picked up at the farther distance.

 

[divingin]

The ONLY explanation I can come up with for these aberrations is, is that from time to time the Lab Radar "picks up" the bullet at different distances. The further away it picks it up, the slower it will read.. I know of no other explanation(s)...

Supposedly, the LabRadar back-calculates the first velocity reading (muzzle velocity.) It triggers from the muzzle blast, then picks up the projectile when it enters the radar beam a little ways downrange. It calculates velocity based on the beam's wave returns, stores the velocity at whatever ranges you have set, and calculates the muzzle velocity based on what it thinks the downrange pickup point was.

That doesn't help with the discrepancies, but it *may* say that you're on the wrong track in figuring it out.

That said, I have no explanation either.

 

[ShootDots]

Supposedly, the LabRadar back-calculates the first velocity reading (muzzle velocity.) It triggers from the muzzle blast, then picks up the projectile when it enters the radar beam a little ways downrange. It calculates velocity based on the beam's wave returns, stores the velocity at whatever ranges you have set, and calculates the muzzle velocity based on what it thinks the downrange pickup point was.

That doesn't help with the discrepancies, but it *may* say that you're on the wrong track in figuring it out.

That said, I have no explanation either.

I am certainly no "techno-genius" and I can not say why there are such discrepancies.. All I know is that from time to time I get, let's say, "readings that should not or probably could not be".. But chronographs serve my purpose whatever model / brand they are. The LabRadar is simply easier and much quicker to set up and pull down than the others>>>> at least that is why I use it!

 

[KenOath]

One thing I’ve done in the settings for the 5 distances you choose for Bullets speed to be read at is have the first reading set at 1m...I don’t know if it was a coincidence but my Lab seems to be reading more consistently from day to day..Generally I’ll get a 10fps difference at most and sometimes it can be put down to cold early mornings..

 

[comagutsa]

Yeah my 1st one is 10 meters Jas.. Will try 1m

 

[Joe Salt]

If you are going out and shooting and not letting the rifle settle in your blowing smoke! Once my rifle is settled in there is hardly a difference in FPS.Have you got new battery's or power pack charged.
And what is it doing on paper? The only time I worry about the speed is if I change Powder Lot#. Then you may see a difference. My two cents!

Joe salt