Magnetospeed V2 Testing

[AlanF]

Has anyone done systematic testing of one of these against other chronos? I just did some today and results in terms of precision were not as good as I had hoped. But before I "publish" it would be good to know if anyone else has done some testing with good results, which could cause me to take another look at my methods.

Alan

[Norm]

Alan, did you use anything under the Bayo strap to stop movement? I found that it needs some non slip material to avoid slight movements under recoil.
This made my readings more consistent.

[AlanF]

Alan, did you use anything under the Bayo strap to stop movement? I found that it needs some non slip material to avoid slight movements under recoil.
This made my readings more consistent.

No I didn't try that. It does have rubber between the spacers and the barrel, so there would be some flexing under recoil regardless of what's done on the strap (top) side. What sort of material did you use?

[Seddo]

The last one I got came with an upgraded strap and a bit of plastic to go over the top of the barrel.

[AlanF]

The last one I got came with an upgraded strap and a bit of plastic to go over the top of the barrel.

There is rubber strip they call a heat/strap guard recommended when you use a sound suppressor, to protect the strap from heat. No mention of needing it for a normal barrel.

There's a lot of them out there - someone else must have done some testing against other chronies. If someone has some good results, I'd like to hear about them. Maybe they're doing something differently.

[Norm]

Alan, did you use anything under the Bayo strap to stop movement? I found that it needs some non slip material to avoid slight movements under recoil.
This made my readings more consistent.

No I didn't try that. It does have rubber between the spacers and the barrel, so there would be some flexing under recoil regardless of what's done on the strap (top) side. What sort of material did you use?

Alan, the Bayo can still move forward with the factory strap and its rubber base.
It only takes a few mm of forward slippage under recoil to stuff up a velocity reading.
I put a strip of non slip rubber matt cut to size on top of the barrel. This stops all movement and definitely gave me more reliable results.

From the instruction manual. (they don't use non slip rubber obviously)!

9) Plug data cord into bayo jack and display unit jack (see
Basic Operations). You are now ready to shoot. Continue
to check muzzle location with reference to the V-block. If
bayo is creeping off, retighten strap with muzzle in
proper position (some creep per shot is normal).

[IanP]

Has anyone done systematic testing of one of these against other chronos? I just did some today and results in terms of precision were not as good as I had hoped. But before I "publish" it would be good to know if anyone else has done some testing with good results, which could cause me to take another look at my methods.

Alan

Alan, unless you test against a known standard chronograph, what point is the test? Testing against another chrono that could well be in error doesn't really accomplish much!

'Publish' what you want as it really doesn't show which chrono is in error. Working in a metrology lab I tested against known standard devices that were NATA certified. This allowed calibration of the device to a real known reference.

Ian

[AlanF]

Thanks Norm. I'll have a look at that.

[BATattack]

I haven't exactly done a full array of "testing" but it seems that slow shots fall low and fast shots land high at long range. Calibration may vary buy it seems to be fairly well in line with my ced m2.

For what it's worth flexing in the mount etc doesn't seem to effect shot speed readings.

[AlanF]

Alan, unless you test against a known standard chronograph, what point is the test? Testing against another chrono that could well be in error doesn't really accomplish much!

'Publish' what you want as it really doesn't show which chrono is in error. Working in a metrology lab I tested against known standard devices that were NATA certified. This allowed calibration of the device to a real known reference.

Ian

Ian,

I wasn't testing for accuracy of the absolute velocity value given, but more for shot to shot consistency (for purposes of measuring velocity variations in loads). It would be nice to have a standardised chrono to test against, but you can still learn a lot about consistency by testing several uncalibrated chronos in series.

Alan

[IanP]

Alan, unless you test against a known standard chronograph, what point is the test? Testing against another chrono that could well be in error doesn't really accomplish much!

'Publish' what you want as it really doesn't show which chrono is in error. Working in a metrology lab I tested against known standard devices that were NATA certified. This allowed calibration of the device to a real known reference.

Ian

Ian,

I wasn't testing for accuracy of the absolute velocity value given, but more for shot to shot consistency (for purposes of measuring velocity variations in loads). It would be nice to have a standardised chrono to test against, but you can still learn a lot about consistency by testing several uncalibrated chronos in series.

Alan

Ok, now I understand!

The two sensors are set at a fixed distance and its not possible for an error to creep in here. If the mount slips forward under recoil the movement is slow and minimal when compared to muzzle velocity so no real error introduced here either.

If you dont have the bayonet array set at the right distance from the bullet path then I have found you can miss some shots. The suggested clearance and the plastic gauge for measuring this distance is 0.25".

The other problem and I think the maybe the biggest, is if your bayonet array is set at an angle to the bore of the barrel. The array needs to be parallel to the rifle bore otherwise you might introduce sensor distance measurement errors because of this angle. The same thing can happen if the bayonet is loose and swings low or high and introduces an angle to the measurement.

If the MagnetoSpeed is attached correctly, (pretty hard to get it wrong) I have found it excellent and much better than my CED. All the muzzle velocities I get I can use in ballistic tables and get accurate drops out to 1000 yards. Thats when I can use G7 BCs for the bullets I'm shooting, Litz has made our sport/hobby much easier as has the MagnetoSpeed.

Ian

[DaveMc]

Alan,
We first took Ians approach here. Originally we tried to find a "standard" shooting through the magnetospeed 2 and what we thought (and really is) a high quality chronograph (PVM-21) as well as beta master and several others to hopefully gain a benchmark accuracy (or standard if you like).

In the end it soon became apparent that our best measure was indeed 1000 yard elevation the PVM was very accurate indeed but still suffered a little from change of light conditions when it seems to recalibrate the background gain - also some occasional triggering errors from shot to shot. The other tested chronies were pretty average to say the best.

The magnetospeed proved to give by far the best correlation between measured speed and height of impact at 1000 yards. So strong in fact that we could reverse engineer the data to determine 1) BC consistency of our projectiles was outstanding and 2) our best barrels were getting under quarter minute "angular accuracy" (which included chrony errors and BC inconsistency). This equated to what we were also seeing in the short range testing. In the end after many tests we have been able to make the conclusion that "our" MS1 and MS2 are within approximately 6-8 fps and much more consistent day to day then any of the infra red or optical screen chronies we looked at.

I will try and get you some of the data via email but Peter Smith has put most of it together and is somewhere down your way now. Have a chat to him in Tassie about it. I am sure he will fix you up down there and may even have some of this on his laptop.

[AlanF]

Thanks all for the responses. Here's what I found.

I used 4 chronographs, being my old F1 Chrony, and 2 CEDs, one fitted with IR screens, the other not, and a new MagnetoSpeed V2 (MSV2) which belongs to the range. The 3 older chronies were set up in series as per the pic below, and the MSV2 strictly as described in the instructions. I used a carbon fibre cleaning rod (see it in the second pic) to check vertical clearance and both vert and hor alignment of the bayonet. The "advanced strapping system" seemed to work well and I didn't notice any slippage over the 15 shots, but didn't measure it. (Norm, I'll use a caliper before and after a few shots today to see if it is moving, because I agree inconsistent movement has potential to cause errors). Temp was about 22, sky was perfectly clear, and time was about 1pm so sun was high. It was the (only) sort of conditions where the CEDs work reliably in my experience.





I was testing my 7 Shehane with 168VLDs and various loads of 2 different powders, around the 3000fps area.

Here are the raw velocity readings :



The mean of all 60 velocity readings was 2999.45 fps. The means of the 4 chronos varied considerably (50fps diff between lowest and highest). I fully expected differences of this magnitude, having done testing in series with my own chronos often. I then applied a shift to the readings of each chrono to bring its readings to the general mean value of 2999.45 fps. So for example the MSV2 readings needed to raised by about 4 fps. So now we have the shifted figures :



Now I do a graph of these figures, and looking at this graph is what led me to say that in my testing at least, the MSV2 results were not as good as I had hoped. The dark blue line representing the MSV2 jumps around noticeably more than the other 3, which are in relatively good agreement with each other. You might be tempted to say that the others all use optical technology which meant they all made the same errors simultaneously. However conditions were consistently bright, and furthermore, the M2 with IR matched the two sky screen chronos well.



It may have been more scientifically correct to apply a scale factor rather than an additive shift to the readings of each chrono, but the resulting graph would have been indistinguishable from this one. And I still need to check for slippage of the bayonet.

Alan

[DaveMc]

Alan - You may or may not be correct here. Indeed there is a danger that the 3 light screen chronies could be picking up the same errors. Interestingly middle of the day was when we found the biggest issues with ours....?????

But the long and the short of it is you seem to have the light screens working well as they are consistent with each other. Assuming the MS2 is out and for this circumstance you have all the light screens working perfectly (a big assumption)- the MS2 was still within 8 fps of all adjusted readings a pretty outstanding result all round. - this is similar to our findings (and I would suggest probably better than this) but the advantage is it does not vary when a cloud comes over, or time of day or some other environmental factor that comes through in the middle of your testing as well as the odd unexplained error.

Providing you clamp it on well, with the same clearance every time then you should get very good results. The same cannot be said for light screens or infrared screens unless you put them in a controlled light room or enclosure.

Either way I would not rely on any brand or type getting you closer than this!

[Norm]

If nothing else Alan, It looks like your load gets faster the more shots you fire!