POI change with Magnetospeed

[DangerRanger]

I only put mine on for velocity data for drops and to check that me SD/ES are good.

some guns it sends 3 moa low, some no different, some 1-2 high

 

[JRanum]

Straightshooter, This is an interesting experiment. Frank Mann did a similer one in 1909, by lowering the muzzle closer and closer to a block of wood beneath it to see what, if any, POI change would result. If I remember right he got close enough to cut a trough in the wood with a bullet with no change on paper until that point. It would seem your theory of the MS not actually interfering with the bullet gasses or flight, but merely 'tuning' in a change of POI is correct.

 

[dunraven]

Use a chronograph for what it was intended: MV. What does it matter about POI? You going to leave it on in a match?

 

[hogpatrol]

I think where some get variations is fixing the bayonet different distances from the muzzle. I use a six inch scale and record the position of the bayonet. I found if I move the bayonet fore and aft, velocity remains the same but the POI changes are different.

 

[sdean]

I think where some get variations is fixing the bayonet different distances from the muzzle. I use a six inch scale and record the position of the bayonet. I found if I move the bayonet fore and aft, velocity remains the same but the POI changes are different.

And that's how you work a tuner. Screw it in or out.

 

[Straightshooter1]

Use a chronograph for what it was intended: MV. What does it matter about POI? You going to leave it on in a match?

it's about curiosity, insatiable curiosity.

 

[normmatzen]

The magnetospeed uses two inductors with magnets for a core so the electric field will impart a force away from the field when the bullet goes by. Simple physics. And, the weight of the magnetospeed also changes the tune of the rifle.
I just use the chrono to do charge changes and find the longitudinal resonance only, I do NOT use it when competing in long range bench rest!

 

[Straightshooter1]

So . . . yesterday I did some various testing, one of which was to see what happens when I turn my MagnetoSpeed 90° to the 9 o'clock position instead of my usual 6 o'clock position. As I've mentioned in the past, in my usual position, I get a vertical POI shift of ~3" to the 12 o'clock and the group is virtually no different from what I otherwise get at 100 yds. When I position the MagnetoSpeed to the 9 o'clock position the POI shifted down ~2.5" from the POA instead of up when it was in the 6 o'clock position. But. . . it not only shifted down it also shifted to the right by ~ 2.5". And thought it shifted down and to the right, the group remained tight (if fact, one of my better 5 shot groups at .227 MOA).

Now, I'm wondering if I can position that the POI will be in line with the POI without the MagnetoSpeed attached. And so, next time I'm out, I'm going to see what happens as I rotate the MagnetoSpeed at 90° increments to see where the POI's land and will report back with pics.

Just FYI for some perspective, I'm firing a .308 24" Krieger sporter barrel.

Ok. . .so, I tested to see where the POI will be if I turn my MagnetosSpeed 360° at 90° increments. There was no change in where it was mounted to the barrel, only that it was rotated. 3 shots at each location starting at the usual mounting position at 6 o'clock, then to 9, 12 and 3 o'clock position. Results were actually just as expected as you can see in the pic below.

Before mounting the MagnetoSpeed I warmed up the barrel with 5 shots to the dot I was going to use for the POA. After 4 shots, I held off of center to try and get the 5th shot on center of the dot to make it easier to line up the crosshairs and luckily managed to get it pretty close to center of the dot. Then I mounted the MagnetoSpeed and began the test, not really making much effort to get a tight 3 shot groups as the size of the groups wasn't the objective. After the test, I removed the MagnetoSpeed to shoot two 5 shot groups to see how this batch of cartridges I loaded might do and that's what you see at the top of the pic.

The distance the 3 shot groups were from the POA was ~2.5" except for when it was at the 12 o'clock position where it was ~3.0" from the POA; apparently some kind of effect from gravity, I'm guessing.

Since the MagnetoSpeed was mounted at the same spot on the barrel, I'm inclined to conclude that the POI shifts were not due to any change (or very little, if any) in the harmonics from the additional weight on the barrel. But the POI shift was due to interference to the air flow coming off the bullet as it travels over the MagnetoSpeeds bayonet being that it's so close to the bullet flight path.

Here's that pic:



PS: These are .308 cartridges loaded with 168 SMK's pushed by 40.9 grs IMR-4064 in Federal brass with CCI 200 primers

 

[Ned Ludd]

Straightshooter - years ago when the MS first came out, several of us using them did the same experiment you showed above, with the exact same results. I don't think it's possible to generate a better picture of what the MS does to POI than yours. Very nice image!

In addition, I and others did many additional experiments testing various various mechanisms by which the MS might affect group size and/or POI. As Straightshooter 1 illustrated so nicely above, the predominant effect on POI is due to muzzle blast off of the sensor deck. Another less direct indicator of this is that devices that either reduce or direct muzzle blast away from the sensor deck, such as suppressors and side-ported brakes, also can noticeably reduce the shift in POI. The tuner effect generated by having the MS attached to the muzzle likely has its greatest effect on group size, rather than POI, which seems to be affected the most by muzzle blast. Nonetheless, all these factors combined contribute to the overall effect on precision when the unit is attached to the barrel.

 

[Bill K]

I use it for what it was intended, not to see how the groups are with it on. I sure as heck don't hunt with it on.
Any chrony, no matter the brand is made to check velocity, not groups.. Anyway that is what I believe.

 

[fatelvis]

Ok. . .so, I tested to see where the POI will be if I turn my MagnetosSpeed 360° at 90° increments. There was no change in where it was mounted to the barrel, only that it was rotated. 3 shots at each location starting at the usual mounting position at 6 o'clock, then to 9, 12 and 3 o'clock position. Results were actually just as expected as you can see in the pic below.

Before mounting the MagnetoSpeed I warmed up the barrel with 5 shots to the dot I was going to use for the POA. After 4 shots, I held off of center to try and get the 5th shot on center of the dot to make it easier to line up the crosshairs and luckily managed to get it pretty close to center of the dot. Then I mounted the MagnetoSpeed and began the test, not really making much effort to get a tight 3 shot groups as the size of the groups wasn't the objective. After the test, I removed the MagnetoSpeed to shoot two 5 shot groups to see how this batch of cartridges I loaded might do and that's what you see at the top of the pic.

The distance the 3 shot groups were from the POA was ~2.5" except for when it was at the 12 o'clock position where it was ~3.0" from the POA; apparently some kind of effect from gravity, I'm guessing.

Since the MagnetoSpeed was mounted at the same spot on the barrel, I'm inclined to conclude that the POI shifts were not due to any change (or very little, if any) in the harmonics from the additional weight on the barrel. But the POI shift was due to interference to the air flow coming off the bullet as it travels over the MagnetoSpeeds bayonet being that it's so close to the bullet flight path.

Here's that pic:

View attachment 1210421

PS: These are .308 cartridges loaded with 168 SMK's pushed by 40.9 grs IMR-4064 in Federal brass with CCI 200 primers

Thank you for That great experiment. What distance was this shot at?

 

[Straightshooter1]

I use it for what it was intended, not to see how the groups are with it on. I sure as heck don't hunt with it on.
Any chrony, no matter the brand is made to check velocity, not groups.. Anyway that is what I believe.

I agree, a chrono is intended for measuring velocities and not groups. But, collecting data and understanding the relationship one's velocities and the related groups helps with finding good loads as well as reducing cost of getting that understanding.

Thank you for That great experiment. What distance was this shot at?

100 yds

 

[Straightshooter1]

Someone in another thread suggested that if the MagnetoSpeed was mounted much lower than recommended so that the compressed air between the bullet and the bayonet wouldn't have any interference resulting in no POI shift. So, I gave that a try today and mounted it really low and increased the sensitivity way up to 9. It definitely did reduce the amount of POI shift, but did not completely eliminate it.

And though the MagnetoSpeed still measured velocities, the measurements were far from accurate. I fired the 1st two shots in the standard configurate to estable normal MV for the cartridges I'm using and got 2745 and 2731 fps. After adjusting the MagnetoSpeed way down, the next 3 shot registered 2687, 2705 and 3835 fps. I decided to take one more shot with the MagnetoSpeed in it's normal position and got 2728 fps.

See what it looked like on paper (the groups above the horizontal line, left and right):

 

[Dusty Stevens]

I havent even seen my magnetospeed since the day the labradar came out. Do they even still sell them?

 

[Ned Ludd]

Yes. There are even pole devices made so that they can be mounted without being attached to the barrel, so as not to affect barrel harmonics. However, such attachments will not necessarily abrogate the effect of muzzle blast from the sensor deck. These attachments aren't exactly inexpensive, either, so someone that doesn't already own a chronograph needs to consider that before buying. I'm of the same opinion, I haven't found a need to use my MagnetoSpeed since I bought the LabRadar, especially after I added the JKL external LabRadar trigger.

 

[rijndael]

However, such attachments will not necessarily abrogate the effect of muzzle blast from the sensor deck.

IME, using a muzzle brake with those off barrel attachments will remove the POI shift.

 

[Straightshooter1]

IME, using a muzzle brake with those off barrel attachments will remove the POI shift.

Hmmm??? Then, I suppose it depends on the design of the break and probably other ballistic factors. . ???

In my tests here, it's all done with a radial muzzle break. And when using a break that only had side ports, it too still resulted in significant POI shift. . . though not as much when the MagnetoSpeed wasn't attached to the barrel.

 

[rijndael]

I've tried it with 2 brakes. Heathen 4 port and a PVA Jet Blast.

 

[Ned Ludd]

IME, using a muzzle brake with those off barrel attachments will remove the POI shift.

Agreed. It should reduce the change in POI due to muzzle blast off the sensor deck by approximately whatever amount fraction of the muzzle blast it deflects away from the sensor deck. In practice, that could mean all, or most of the POI change. Some MagnetoSpeed users have reported very little, if any, POI change with braked rifles.