What's going on with my Magnetospeed V3?

[TheGerman]

Already called and left them a message and am going to re-test it on Monday, but had something really odd happen with my otherwise flawless Magnetospeed yesterday that I can't explain.

Took the same rifle, with the same loads out for testing and velocity logging. Had a range of identical loads that I had shot during 2 other testing sessions; the only difference is the powder charges as I was increasing them by .3. All powder charge ranges had been shot 2+ times in the past and logged as well as temperature.

Same gun, same magnetospeed - I start shooting as usual and notice all the velocities, while near each other, were at least 150fps BELOW the velocities from the other 2+ testing sessions with temperatures in the mid 70s to low 90s. Nothing erratic, no 'regular' velocities and then something very high or very low, S/D on all strings was 10 or less so it wasn't the magneto reading them weird or something happening with the unit moving or something coming lose, etc. This was consistent over 50 rounds - all strings of 5 were relatively close to each other velocity wise, low S/D, but were 150-200fps BELOW the velocities from previous sessions.

The only obvious thing to me was that yesterday it hit 111 degrees outside while I was shooting. Would the sun and heat interfere with the readings? I'm betting sitting in the sun baking it was 130+, there were mags I had left laying out next to me and I couldn't pick them up after a few minutes. Could the sun and heat be the problem?

What really confused me was there was zero pressure signs or signs to show the rounds would be erratic. Everything grouped very well as usual. The magnetospeed started this from the very first shot, so it wasn't something that all of a sudden started happening after 10 rounds or 30 mins,

What gives?

 

[diverdon]

I never had anything like that happen, then I've seldom retested a load once I have the mv. Of course I agree that the heat may have something to do with your strange readings. Also I wonder how your batteries are. Toward the end of the battery some devises can act funny. Perhaps next session bring a new battery shoot one series then change the battery and see if the results are affected.

 

[eklarsen]

Nothing wrong with the magnetospeed, it is well documented that environmental differences will affect MV, in this case hotter, you didn't mention but did you clean your rifle or any other changes? Typically when it is hotter MV will increase but anything can happen with different environment. I see you are in Afghanistan so I assume you didnt hand load these round but differences in seating depth, even very small deltas will cause different MV as well, I wouldn't sweat 150-200 FPS.

edit: Sorry maybe not in Afghanistan any longer, if you did handload it could be slight differences in seating depth as well.

 

[nfoley]

^^^ - You wouldn't sweat 150-200 fps? That is a big change to blame on environmentals. If anything the increase in temp should have raised your MV, not lowered.
Am interested to see if something is going on with your magnetospeed.

 

[TheGerman]

^^^ - You wouldn't sweat 150-200 fps? That is a big change to blame on environmentals. If anything the increase in temp should have raised your MV, not lowered.
Am interested to see if something is going on with your magnetospeed.

That's the main reason I took these rounds out again. I have a large load development spreadsheet and keep velocities, temps and all sorts of things documented. One of the things I wanted to get was the change in velocity as well as if I would run into pressure issues with loads I had that did well in 80 degree weather, are now being shot in the 110+ degree weather we get here part of the year. Didn't clean the barrel or change anything since the last round of shooting a few days prior.

I was expecting a bit of a change in velocity, but not a 150-200FPS drop, which is why I think there's an oddity due to either the extreme temp or a battery issue. Had it just given me a bunch of erratic data, I'd simply chalk it up to heat. But the data was a 150-200fps drop in all velocities across the board, with low S/D; it was like it was taking the normal velocity and subtracting 200 from it every time.

I'm curious what they say tomorrow when I speak with them and if extreme heat (I'm betting the bayo got to 140+ degrees in the sun) is a known issue that causes this. Or who knows, it may just be the battery or a total random fluke I'd never be able to recreate?

 

[diverdon]

I wouldn't sweat 150-200 FPS.

What is the longest distance at which you routinely ring steel not sweating 150-200 fps differences?

In .308 I have tested several different powders and typically the deviation on the loads I shoot is about .5 fps/deg. So unless something quite different than ordanary temp on powder effects is what is happening here I doubt that could even account for 50fps. I'm inclined to agree with the German that for some unknown reason the V3 is returning incorrect results.

Sorry maybe not in Afghanistan any longer, if you did handload it could be slight differences in seating depth as well.

He is German, if he handloaded the bullets the seating depth is an order of magnitude more precise than most factory loads.

 

[sjoliat]

I don't know the exact anatomy of the bayonet, but I am guessing there are multiple sensors that detect the magnetic field. It seems reasonable that given the extreme temp and expansion of materials, the distance between sensors would have increased, as would the time between sensors - reading like a drop in velocity. Just my thinking anyway..

 

[mark5pt56]

I don't understand the lower readings, not sure if the display box could be affected by the heat. That shouldn't matter though since the data is from the bayonet. Did you check the bayonet surface, insure there's no "skipping" marks on it and same spacers, etc--just checking? I had 20fps less from the same loads, I'm certain it was from the 15 degrees less temp and clouds vs sunny and a clean barrel.

 

[Danhalen7.62]

I know you are developing, but I would check your dope. 150-200 fps would be a VERY noticeable difference. 308 shooting 175's would be around 1.5 mil difference @ 1k... At least you would be able to narrow it down to your chrono or ammo.

 

[nfoley]

Any update on this German? Curious if magnetospeed had any comments as to cause of your readings.

 

[TheGerman]

Any update on this German? Curious if magnetospeed had any comments as to cause of your readings.

Spoke with them and was planning on shooting it again last night but we had torrential rain all evening/night/today. Hoping to go out tomorrow and try it again.

The guys at MS were under the impression it isn't the unit because the ES/SD were consistently low. I confirmed that heat does nothing to the unit as they explained to me that while the bayonet is polymer, the actual parts that get readings are a high grade metal (forgot the type it was) where extreme heat may change a reading by a few FPS, but nothing like 150-200FPS. Extreme cold is actually worse than extreme heat I was told.

I tried to come up with every scenario I could think of that the MS could have experienced. From heat, to would it have been possible to add/remove a spacer since last time, still get a reading but since the height was different the reading would be different? All things they've heard of before and tested, nothing that would do this so consistently.

Changing the battery shouldn't change anything (even though I'm going to) and we kept circling back to same ammo, same gun, low S/D, low E/S every 5 shot string the entire time = not a high chance its the unit.

We'll see what happens when I shoot it again.

 

[diverdon]

I guess I have to wonder which number trues up between your ballastic software and your actual drops at range. Then I wonder if it is possible that something changed in your load. Did you recently open a new can of powder or a new box of primers? If you use a powder trickler is is possible that it somehow became uncalibrated? Has anyone else been near your reloading equipment?

There is a guy who lives near me, whose son used his reloading gear. One day the story goes, the son poured the left over Blue Dot into the Varget can, subsequently dad ended up with a 30-06 that out preformed .300 Winchesters until that batch of powder was gone. (That story is probably Bull)

 

[TheGerman]

I guess I have to wonder which number trues up between your ballastic software and your actual drops at range. Then I wonder if it is possible that something changed in your load. Did you recently open a new can of powder or a new box of primers? If you use a powder trickler is is possible that it somehow became uncalibrated? Has anyone else been near your reloading equipment?

There is a guy who lives near me, whose son used his reloading gear. One day the story goes, the son poured the left over Blue Dot into the Varget can, subsequently dad ended up with a 30-06 that out preformed .300 Winchesters until that batch of powder was gone. (That story is probably Bull)

That's the thing, the rounds are from the same batch. So unless I managed to have something change during the process and then managed to somehow grab all of the higher velocity rounds and leave all the lower velocity rounds at home, I don't see how a change is possible.

Trust me, I already went backwards over the rounds as this has been bothering me and is a bit of a mystery. Checked the brass to make sure it wasn't a different maker, checked what primers it was, ran check weights on the power thrower, went over anything I could.

 

[diverdon]

If it were me I would locate a second corono to check with.... But if like me you hate borrowing shit, then on to plan "b." set up a target at 1000 generate a solution using each MV with your solver. (for one bullet I use the numbers might be 9.2 and 8.0 mils. See which solution works best. If it is the solution that matches current results then at least your numbers are good now. If it takes the old numbers to get hits then it might be time to get a new cronograph.

 

[sheepdog697]

I know you are developing, but I would check your dope. 150-200 fps would be a VERY noticeable difference. 308 shooting 175's would be around 1.5 mil difference @ 1k... At least you would be able to narrow it down to your chrono or ammo.

I agree with what he said. If you check your dope, you should be able to go back and correct your MV to what your field dope is. Then you can go from process of elimination.