Most discrepancy you've seen with Magnetospeed?

JasonMPD

Testing ammo in my new 12.5 SBR, the Frontier (Hornady) 75gr HPBT Match 5.56 NATO spec ammo was measured by the Magnetospeed at 2609 FPS (15 shot average).  That's fast for 68+ grain bullets in a 12.5" barrel, but possible? Maybe?

Anyhow using trajectory validation in two programs (Strelok Pro and BallisticARC) they agree the MV is more like 2300 FPS.  0.395 G1 BC @ 2609 would drop 4.0" from a 100 yard zero at 205 yards.  My observed drop is 5.65".

However, yet another variable, it's a 4x scope with a CQC style donut reticle with a dot in the middle.  Could I miff a shot group low by 1.65" with that reticle?  Sure could.

So not yet assuming it's the chrono, has anyone seen a broad discrepancy with a Magnetospeed? 

Pegasus

My Magnetospeed has not exhibited any discrepancy that stands out.  The readings have always been right where I expected them to be.  I've only been using it with .308 and have not chronoed any .223 in years.

mitdr774

6.5x55, 24" barrel, 160gr RN, book load of 2250 FPS.  Only did one quick test shot to see if they would even read close.

Magnetospeed 2106 FPS
Caldwell at 15' 2110 FPS

This was with a rifle that has always seemed to come in low on velocity compared to the book.

Ernie Bishop

You could always have a malfunction, but I would check other known MV's and see if they are off or not.  Old battery???

JasonMPD

Ernie Bishop said:

You could always have a malfunction, but I would check other known MV's and see if they are off or not.  Old battery???

Barring the hypothetical error isn't me shooting low of my mark and me assuming it's bullet drop, those are my next troubleshooting points.  I went ahead and changed the battery and made sure the firmware was up to date.

Ernie Bishop

Well, reconfirm your drops with proving shots at distance.

Then if they don't match the software, I change the software until it matches my drops, or I can recheck my zero, and go through the process again.

The main thing is knowing where your shots are going to hit at any distance you will use it at.  One can do that without software or a chrono...Old School!

earlyagain

Is it possible that the varying internal dimensions of the 5.56 cases (by manufacturer) in combination with varying throat dimensions, varying barrel rates of twist etc., are causing the discrepancy???

Zee

My chronograph velocity and trued StrelokPro velocities do not always match. 

So what. 

As long as my drops are correct, I don’t care what velocity StrelokPro has to use in its program brain to get them for me. 

I chronograph my loads. Put that data in StrelokPro. Shoot the data. True the data. Get the results I want. Charlie Mike. 

Don’t sweat the small stuff. 

Only hits count. 

Pegasus

I had another session with my MagnetoSpeed on Sunday as I ran a quick ladder test.  The velocities for the 7 loads were right in line with my expectations and the best one also had the lowest SD, single digits.

I liked that from the first shot, the MS detected the bullet and showed the velocity.  The only thing I dislike about the MS is its silly strap; it's difficult to set so it doesn't slip.

Zee

Pegasus said:

I liked that from the first shot, the MS detected the bullet and showed the velocity.  The only thing I dislike about the MS is its silly strap; it's difficult to set so it doesn't slip.

This. 

JasonMPD

Zee said:

Pegasus said:

I liked that from the first shot, the MS detected the bullet and showed the velocity.  The only thing I dislike about the MS is its silly strap; it's difficult to set so it doesn't slip.

This. 

Mine slips a little on barrels with sporter tapers, not so much on others.

JasonMPD

Zee said:

My chronograph velocity and trued StrelokPro velocities do not always match. 

So what. 

As long as my drops are correct, I don’t care what velocity StrelokPro has to use in its program brain to get them for me. 

I chronograph my loads. Put that data in StrelokPro. Shoot the data. True the data. Get the results I want. Charlie Mike. 

Don’t sweat the small stuff. 

Only hits count. 

Oddly enough I bring this topic up because I was expecting something like 2400fps and MS said it was 2609fps. In a 12.5" barrel with 75gr ammo.  

Perhaps I jumped to conclusions about the MS/Strelok/BallisticARC.  And I certainly need to shoot a lot more of these rounds and do what I can to get space for 400+ yards.  I need better drop data at greater distances.

Spk

I'm leaning towards the scope. Is there any other scope you can mount on it to compare the two? Prehaps something with a crosshair. Just for comparison.

Unless you're shooting for score, I think the setup you have now would get the job done. On the other hand, if it's for precise work applications then I can see why you would want to resolve this issue.

Try another scope so you can rule that out or replace if necessary.

JasonMPD

Spk said:

I'm leaning towards the scope. Is there any other scope you can mount on it to compare the two? Prehaps something with a crosshair. Just for comparison.

Unless you're shooting for score, I think the setup you have now would get the job done. On the other hand, if it's for precise work applications then I can see why you would want to resolve this issue.

Try another scope so you can rule that out or replace if necessary.

The setup now is the intended setup, but once I save for it a NF NXS-8.  It's the size of most 1-4x, but is 8x FFP.

I have a 3.5-21x scope I'll use to get better verified velocity and drop data.