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Well maybe this doesn't really explain all those outliers, but what a surprise I had yesterday afternoon when I simultaneously chrono'd 34 rounds of HPR 55 gr VMAX with LabRadar and MagnetoSpeed. Actually, I'm not sure what to make of any of it, but more about that momentarily.

This was shot with a SBR consisting of a BCM 11.5" LWE barrel with an Adams Arms piston, and a Liberty Triumph suppressor. Here's a couple of pics of the gun and the set up:





Oops, wait that's the pre-setup pic. Here's the setup:






Here is a graph of the velocities I collected with the two units. Actually, I forgot to arm the LR on the first shot and to keep from having a "0" for the first shot, I edited the "0" to a velocity "in the neighborhood".

What you're looking at is a plot of the two velocities; you can see they essentially track but with an offset. There is also a line for the MS average and another line for the LR average. But of immediate interest is the three peaks - why are they there? And notice BOTH chronos show the spikes.

The average for the LR readings is 2420 fps. The spikes are, shot #6 = 2671, shot #13 = 2595; shot #25 = 2633. Those peaks are 251 fps, 175 fps, and 213 fps respectively above the average.



I can't say that I've seen such deviations in velocity with this ammo before. I am immensely glad I was running two chronos or I would have to suspect chrono error - but they both show the peaks, so...

Could this be as simple as the factory got three rounds a loaded a little hot in this lot? Or is this typical?

I can guarantee you I'll be chrono-ing all my HPR ammo for a while - every shot!

Next is which chrono is more accurate? LabRadar specifies an accuracy of 0.1% - that's right, one tenth of one percent. And MagnetoSpeed claims near that accuracy as well, yet the two vary in % difference in measurements anywhere from 0.61% to 2.11%. Which one is right? We may never know.

But this does reveal that ammo can have exceptionally high velocities that we may not know about when we're shooting it.
 

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That is 3.5" difference at 200, and .75" at 100. Outliers that I see, even with you are in excess of 1.5" @100. Mine I shank, and I know it as soon as the hammer falls.

I've crono'd my homebrew and my earlier rounds had a high deviation (100 fps), but after I learned more with rife reloading, my more recent cooking shows 30fps. I have more QC involved now. Factories have little to none other than lot numbers which are in the 100k range probably.

Federal Match ammo has (had) an acceptable variance of +/- .4 grains. Nothing leaves my bench more than +/- .2 grains for mass production rounds. ( I think those are the numbers. Have not cooked any since 2013. I know it's 4 for Federal and mine was 2. Might be .04 and .02...)
 
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I have an RCBS electronic powder dispenser that for the most part, is very accurate. But every so often, it will kick out a load that has a couple of tenths more grains of powder than I have specified. When I catch them, as I usually do, they go back in the dispenser. But if I miss one, and I am sure a few have slipped through, it will make a difference.
 

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Next is which chrono is more accurate?

A man with 2 watches never knows exactly what time it is. :biggrin2:
Well, heck, time is merely a creation of our minds, anyway so we don't have to exist in a void.

Sent via my subspace communicator
 
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Discussion Starter #6
That is 3.5" difference at 200, and .75" at 100. Outliers that I see, even with you are in excess of 1.5" @100. Mine I shank, and I know it as soon as the hammer falls.

I've crono'd my homebrew and my earlier rounds had a high deviation (100 fps), but after I learned more with rife reloading, my more recent cooking shows 30fps. I have more QC involved now. Factories have little to none other than lot numbers which are in the 100k range probably.

Federal Match ammo has (had) an acceptable variance of +/- .4 grains. Nothing leaves my bench more than +/- .2 grains for mass production rounds. ( I think those are the numbers. Have not cooked any since 2013. I know it's 4 for Federal and mine was 2. Might be .04 and .02...)
Yep, Sticks, that's a pretty good summary of the situation.

With the Aus Outback 69 gr ammo I often shoot, the SD is pretty typically 35 fps and I shoot it in anything from a 10.5" barrel to an 18" barrel. I see about that SD of 35 fps within all barrel lengths, i.e. not from barrel to barrel obviously.

With the HPR 55 gr VMAX where the three peaks showed up, I typically see SDs of about 40 fps. In fact, I chrono'd another 62 rounds of this ammo from another can this weekend through a 16" barrel and got the following results which isn't bad at all:

Vavg: 2617 fps
High: 2741 fps
Low: 2526 fps
Ext spread: 215 fps
SD: 42.8 fps

I plan to continue to chrono this ammo with the LabRadar (because I can change guns, just by changing guns) to see if the anomalies show up again. I'm kinda thinkin' this may have been a run issue.
 

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Next is which chrono is more accurate?

A man with 2 watches never knows exactly what time it is. :biggrin2:
Yeah, that is perplexing although in my trade, getting slightly different measurements from two instruments is not uncommon :icon_neutral:

True, but I guess we could observe that a man with two watches KNOWS he never knows exactly what time it is :tongue:

OTOH, a man with only one watch may not know he doesn't know exactly what time it is.

Which one is more accurate is a tough nut to crack. What do we compare to? I guess I'm just gonna have to accept that one or the other, or both could be off by 1 or 2 percent. I suspect the same conundrum exists with light screen chronos. But since we typically just use the one chrono, we assume it is perfectly correct - at least I do! :tongue:
 

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So, how do you like the LabRadar?

I am trying to decide whether or not I can justify the cost of one, since I already have a Chrony Beta. The main benefit I see is the ease of setup, but I am wondering what else there is that might justify the cost.
 

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So, how do you like the LabRadar?
I really like it.

...I am trying to decide whether or not I can justify the cost of one, since I already have a Chrony Beta. The main benefit I see is the ease of setup, but I am wondering what else there is that might justify the cost.
Well, now there's the hard part. It does pretty much what any chronograph does - measures bullet velocities. The LR (LabRadar) compared to the Chrony has these advantages:

- Much easier to set up
- doesn't require a cold range to set up
- doesn't require good lighting conditions, etc.
- you don't have to shoot through a little triangular area
- measures velocities at the muzzle rather than 10 feet or so down range
- doesn't measure average velocity over the distance the light screens are separated
- works when it's raining
- it's easily re-positioned if you need to shoot at a different target(s)
- Has a review mode to review the strings measured
- will measure arrows
- changing guns is as simple as changing guns

and not sure how useful this is, but it does it

- measures muzzle velocity plus velocities at 5 user set downrange distances - I get about 75 yards with .223/5.56 and 90 yards about 60% of the shots
- downloads data right into an Excel spreadsheet

Some downsides are:
- Pretty tough on batteries (6 AAs); I use a USB rechargeable battery pack I already had and it is great!
- may pick up bullets from other guns, although its software does discriminate against shots from other guns entering the radar beam.
- if used with a suppressor, you probably are gonna need the optional air gun mic - I use that because I only shoot with suppressors
- with long barrels or somewhat shorter barrels with suppressors, the muzzle may reach beyond the shooting bench and since you need to set the LR even with the muzzle, or close, you may not have a place to set the LR. However, a tripod would solve that problem. You would have to use a tripod with the Chrony also.
- as with light screens, i.e. chrony, you can only shoot one target at a time without re-positioning the chrono.

And this is kind of a biggy:
- LR limits you to about 1 shot every 2 seconds. Of course a Chrony probably does too, not because of timing restrictions but because you have to be sure you've got your gun re-aligned properly so you don't shoot the chrono.


Then there's the MS (MagnetoSpeed). It has similar advantages of the LR except it won't measure arrows, a little difficult to use with pistols and especially revolvers, and it doesn't measure downrange velocities. It has to attach to the barrel and that can be a little tricky and sometimes somewhat arduous. And that attachment to the barrel is a bit disquieting in that you can't help but wonder what it's doing to accuracy and precision. I have, in fact, seen the POI raise by 1" on a lightweight barrel when I removed the MS off the gun.



However, the MS has no bench restrictions like the LR might. And you can shoot multiple targets since the MS is mounted on the barrel and moves with the gun.

Plus there's no rate of fire limit with the MS until you get close to full auto fire, but it has a full auto mode but I've never used it, so I really don't know how well it works. I mean, if it's so good, why not just always have the MS in the full auto mode???
 
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