LabRadar Accuracy With Small Bullets?

[piie]

Go to Thingyverse and search for "sight for Labradar ballistic radar" - it works quite well - you only need to get hold of a 35mm M5 bolt to fix it, and it's free (if you have a 3D printer that is)

 

[FeMan]

A buddy was having issues with his lab radar getting readings for 6mm bullets. I looked at the settings and found his was set for a 300-grain projectile. When I set if to 105, it started reading reliably. This did convince me that the settings made a difference and now I stop and set it to the bullet weight I am testing. It may not solve all of your issues but if your projectile settings are different than what you are shooting, you might try adjusting them. I have found that the setting for unit offset from the barrel makes a difference in the reliability of readings (not necessarily accuracy though).

 

[flyingbrass]

I like the idea of attaching a scope or red dot. We've been using a square and eyeballing the alignment to the target. LabRadar dropped the ball with their dinky alignment system.

My barrel position in relation to the unit has varied between sessions. Initially, we had trouble getting the chrono to trigger on any shots at all, and this was with bare muzzle .223 AR-15's. Muzzles had to be within a few inches of the unit, and this was when set at the most sensitive. We had to turn the Tx power down to low to get velocity readings.

Later I attached an A2 flash hider, and my buddy put on a muzzle brake. With the flash hider I need to keep the muzzle slightly behind the unit, and within 4-5 inches or it won't trigger. We have it set on the 6" muzzle distance setting. My friend's muzzle brake allows a little more leeway than the A2 flash hider, but not by much, and the sideways bark from that thing is substantial. This is at the most senstive triggering setting. I don't understand how others are having their LabRadars triggered by nearby shooters at any setting. We have to deliberately give this one the most blast possible for it to pick up a shot at all. Maybe it has a problem.

We'll chrono again next shooting session, this time shooting from a table instead of from the ground. I'll do my best to measure and record my muzzle position in relation to the chrono. Will then try to repeat with the same positioning the following time and compare results. I'll save some rounds from the same reloading batch to run the next session.

If consistent position increases repeatability, it still won't say very much about accuracy.

Speaking of chronograph accuracy/precision, I encountered an odd situation a couple years ago that provided some interesting information.

I had been shooting through my ProChrono from the bed of a pickup. I moved the chrono, still on its tripod, several feet to the side when my friend shot his rifle. I noticed the ProChono was registering his shots and velocities. Bullets were not passing through the chrono. It picked up the shockwaves.

Here is the e-mail I sent him about the results:

The chrono was registering about 1180 FPS during your shots. It was picking up the shockwave at the speed of sound.

Sound speed at different temps:

80 degrees: 1139 FPS
100 degrees: 1160 FPS
120 degrees: 1180 FPS

The air temperature wasn't 120, probably more like 85. The readings are slightly off because the chrono wasn't perfectly lined up with the origin of the sound. It was rotated a little, reducing the distance between the sensors, which caused the velocity readings to be calculated higher than actual.

Similar happens with bullets, which is why it is important to keep the chrono lined up so bullets travel parallel with the top of the chrono. If the bullet goes through at an angle, it travels more distance between the sensors than is being calculated. If shooting through at an angle, readings will be lower than actual bullet speed.

Since the speed of sound is constant at a given temperature, this was a good measure of the chronograph's precision. 12 shots were recorded.

high: 1192
low: 1180
avg: 1186
es: 12
sd: 4

Specs for the ProChrono say accuracy is "+/-1% of measured velocity, or better." I can't vouch for accuracy, but precision was better, at least this time for a single string of 12 "shots". The ES of 12 is a total variation of 1.01% (+/-.505%).

If the error is linear, which it may be, 1.01% would be an extreme spread of 27.3 FPS at 2700 FPS.

Based on the collected data, that's what the chrono would show if you could fire shots all going at the same exact speed. It's not capable of measuring super tight extreme spreads. Sure, it will occasionally report some low extreme spreads in strings of small sample size, but they don't mean anything. It's akin to reading ten-thousandths on calipers only precise to .001".

 

[flyingbrass]

We had been using the Labradar from prone position, with the chrono positioned above the barrel. In the wash we were shooting in we had to turn the transmit power down to low or we wouldn't get any readings.

Now we've shot twice at a different location from a bench. MInimal ground clutter allows the use of normal Tx power. The Labradar tracked bullets to at least 50 yards. I haven't seen the raw data, so I don't know exactly how far. I used the same batch of reloads both times. Temperature was the same within a few degrees. Barometric pressure was about the same. My muzzle position changed slightly between sessions because I found that the end of my A2 flash suppressor needs to be slightly behind the chrono for it to trigger reliably.

Average velocity for session #1 was 2777, and session #2 was 2761. Sample sizes were small, and ES with the ammo is usually 30ish, so I consider this fairly consistent. I suspect more rounds would have brought the averages closer together.

My friend also fired ammo from his same batch both times. He shot 10 round strings, and if I remember correctly his average velocity on trip #2 was about 10 FPS slower. His loads have similar ES to mine, so again the chrono seemed reasonably consistent between sessions. At least there weren't any big unexplainable changes like I had been getting before. Time will tell if this repeatability continues.

During session #2 I measured my muzzle position in relation to the chrono and will try to use the same in the future. So far, it is looking like being up off the ground and using full transmit power has improved consistency.