POI change with Magnetospeed

[Eric Leonard]

I usually test loads for group and then check for speed and consistency with the chrono,,between showers this morning I was working on new lot of 105 VLDs and new hotter lot of H4350 and got my speed and ES back where I was but with about .6 grs less powder,

after shooting groups I put on the Magnetospeed the POI was 3/4 high and 1/2 right from where it was without it on,,accuracy was about the same,,

what is everyones SOP on workin with this chronie,,do you test with it on and get good data and trust your zero or do you only test speed after finding a load

I shot a couple strings with another powder that looked very good at 100 yards but ES was 50 fps and I cant live with that ,,4350 load is in single digits ever time and pretty temp stable also

 

[DennisH]

I get my readings which I feel are pretty accurate.

Then I remove the Magnetospeed and zero my scope in.

Just my opinion and process.

Dennis

 

[Comrade Terry]

I prefer to test the velocity after finding the load. After that, I can zero the scope with just a few rounds.

I'm not interested in the velocity of loads which I'm not going to use.

 

[RDavies]

Nearly everyone finds the POI will climb when you put the magetospeed on, though it stayed similar when I had 2 magneto speeds on, one with the bayonet on top and one below (I was checking one crono against the other). I start all of my load development with a crono before I go to paper as I don't have enough opportunities to shoot long range to test groups on paper which show bad ES/SD. Once I get a powder/primer/jump or jam combination which works well on the crono, I will do a ladder test, then fine tune some powder loads and seating depths.

 

[Joe R]

gstaylorg said:

The MS can change POI as well as group size/shape. It can act like a barrel tuner...there is no way around it. Although not everyone experiences large changes in POI....

I was at the range shooting through my Oehler and a guy asked me if he could strap-on his MS onto my barrel so that we could compare velocity. I did and the velocities were almost identical, but I expected the MS to effect my POI but if you take a look at the target below you can see that there wasn't much change in POI, but the groups did improve. Just saying...

Joe

 

[snakepit]

What was the distance you were shooting at?

 

[Eric Leonard]

100 yards

 

[Boxcar77]

I prefer to test the velocity after finding the load. After that, I can zero the scope with just a few rounds.

I'm not interested in the velocity of loads which I'm not going to use.

Couldn't have said it better myself! Concise and too the point.

 

[tonysnoo]

My magnetosphere changes my poi at least 1.5 minutes high. It doesn't always change grouping, but can slightly. I like to develop and then find out what speed, too.

 

[dmoran]

For those who are only concerned with the speed of there load and deviations, you don't need a chronograph at all (for distances greater then 100yds). Simply by adjusting the velocity of a ballistics program (JBM, AB, etc.) to the actual drop of the POI's on the target(s). That can yield more accurate and/or "true velocities" and deviations then many chronographs are capable of, that will be unique and true to your rifle barrel, bullets, and load.

Also a good way to check and/or calibrate a chronograph.
Donovan

 

[tonysnoo]

The whole point of testing velocity during load development is to find the boundaries of the charge weight node that shows low ES/SD so that you can then set your charge weight at the center. Group size/shape can influence the final determination of charge weight to some extent, but I'm more concerned initially with the velocity data. Groupings within the node during charge weight testing often are not the greatest. However, I'll fine tune the groups afterwards by adjusting seating depth. How is it possible to know the boundaries (width) and the center of the node if you only determine MV after "finding the load"? If that approach works for you, great, but I really want to know my optimal charge weight is centered in a node where changes in charge weight have the least effect on MV/ES/SD. That is the load that will show the greatest resistance to changes in temperature/charge weight measurement, etc. during a string of fire. In any event, I've seen groups both shrink and expand with the MS attached. It all depends on the caliber/bullet/charge etc. So I choose to take it off and shoot groups separately from MV determination. YMMV.

I don't develop based on groups, but do follow the line of reasoning of group placement vs poa. I'm sure there are lots of ways to determine a node, that's the one I like.

If you work solely based on chronograph readings, the magnetospeed may be great, then take it off to tune on the load you want.

 

[bsumoba]

Mine actually changes and throws my rounds low about a minute.

Develop the load first, then when it is nailed down, run the velocities on a separate firing. Yes, it sucks to not be able to check velocities while doing a ladder or OCW test, but you will at least get really good muzzle velocity numbers.

 

[Lapua40X]

... I like my MagnetoSpeed far better than any other chrono I've used due to its ease of use and reliable readings.

I prefer to test the velocity after finding the load. After that, I can zero the scope with just a few rounds.
I'm not interested in the velocity of loads which I'm not going to use.

Pretty much sums up my opinion ..... 8)

 

[dcali]

You don't need to chrono a ton of rounds.

You can take advantage of the fact that velocity to charge weight relationship is very close to linear over a small range of charge weights. It only takes a few shots to get an idea of what velocity will be at any reasonable charge weight. Use a min load, a max load, and two or three in between.

If you plot those in a spreadsheet (charge weight vs velocity), you should see something pretty close to a straight line that you can use to predict velocities you didn't test for.

Then, once you find your accuracy load, verify with another 10 or 15 shots to get a feel for the velocity SD.

 

[fx77]

Prefer to get the best groups and then use the chrono data to print out a table of comeups/drops, etc.

 

[savagedasher]

Yes it can change the point of impact and also change your tune . Why would someone not use a crony when working up a load. My self I would rather have a less accurate crony then one the effects my tune.
Larry

 

[Rpbump]

Like many shooters I try shooting groups first then chrono. Using the MS on heavy/bull barrels I've not experienced a shifting of groups.


Rpbump

 

[mfieldsii]

I was checking my zero and my 100 to 200 yard drop. Did a 4 shot group at 100 yards with no magneto speed. put 4 bullets on the bullseye all 4 touching and under a dime.

Move to 200 to do a 4 shot group. First one shot was exactly 2.6" drop just as ballistic calculator says it should. I then decided to throw on the magneto speed to see if my MV changed with a new canister lot of the same powder i use had changed. My shot jumped 3" on my next 3 shots!!! I could not believe it. Only thing changed was the magneto speed. So I pulled it back off and shot one more and back down next to the 1st shot it went.

So yes, 1.5 MOA it can definitely throw it off.... I would imagine it would vary by load and barrel etc. Still not sure why it climbed 3" instead of going left right down or variation, etc. I presume that has the bullet leave the barrel and the bonnet being so close to the bullet as it is accelerating it may getting a little bump up out for the barrel.

 

[Straightshooter1]

I was checking my zero and my 100 to 200 yard drop. Did a 4 shot group at 100 yards with no magneto speed. put 4 bullets on the bullseye all 4 touching and under a dime.

Move to 200 to do a 4 shot group. First one shot was exactly 2.6" drop just as ballistic calculator says it should. I then decided to throw on the magneto speed to see if my MV changed with a new canister lot of the same powder i use had changed. My shot jumped 3" on my next 3 shots!!! I could not believe it. Only thing changed was the magneto speed. So I pulled it back off and shot one more and back down next to the 1st shot it went.

So yes, 1.5 MOA it can definitely throw it off.... I would imagine it would vary by load and barrel etc. Still not sure why it climbed 3" instead of going left right down or variation, etc. I presume that has the bullet leave the barrel and the bonnet being so close to the bullet as it is accelerating it may getting a little bump up out for the barrel

I get that much shift in POI when I have my MagnetoSpeed mounted on my 24" sporter barrel. But I don't think it has to do with any interference from it as the bullet leaves the muzzle. One should be able to test that simply by mounting it at 90° instead of the usual. If fact, I was going to test that last week and forgot. But I give that a try next time out and see.

One of the surprising things for me was not that there was a POI shift, but with that shift, I was still getting the same (or very, very close to the same) precision as I groups remained as tight as without it. I've seen some others reporting the same, and others who didn't get the same precision. So, I guess I'm just lucky as that helps with getting chrono data at the same time as doing a load development.

 

[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.