Predicting difference in POI?

[CliveWard]

Hi All,

 

Just out of curiosity. Is there a rule of thumb or even bit of software that can predict the trajectory change from one load to another where the sight setting remains unchanged?

 

At the moment I have my .22 Hornet zeroed to impact 1" high at 100 yards with the 35 grain V-Max at 3000 fps (.109 BC according to manufacturer).

 

I want to develop another load to use in the rifle with the H&N 45 grain RN running at around 2450 fps (.125 BC according to quickload).

 

Bore to sight line is 2.35".

 

Any ideas how much lower the POI will be with this slower but better BC bullet?

 

 

Cheers

 

 

 

 

 

Clive

[Grum87]

Ive found in the past, if you're willing to play with the ballistic calculator you can get a decent estimate of the offset by setting up both loads for a 5-10yard zero, and plugging 100 yards in to get the drops.

 

With such a short 'zero' the difference in POI would be non existant, from then on it's just physics at work.

 

Worked for me.

[CliveWard]

Hi Grum,

 

Thanks for the info. Just given that a whirl and the heavier slower load should be approx 1" lower POI which would be perfect.

 

 

Cheers

 

 

 

 

 

Clive

[jcampbellsmith]

Hi All,

 

Just out of curiosity. Is there a rule of thumb or even bit of software that can predict the trajectory change from one load to another where the sight setting remains unchanged?

 

At the moment I have my .22 Hornet zeroed to impact 1" high at 100 yards with the 35 grain V-Max at 3000 fps (.109 BC according to manufacturer).

 

I want to develop another load to use in the rifle with the H&N 45 grain RN running at around 2450 fps (.125 BC according to quickload).

 

Bore to sight line is 2.35".

 

Any ideas how much lower the POI will be with this slower but better BC bullet?

 

 

Cheers

 

 

 

 

 

Clive

Clive

 

You need to field test both loads to see what actually happens. Set up your target at 100 yds and fire 3 shots of each load at it.

 

Regards

 

JCS

[gbal]

Clive,actual POI isn't usually just a vertical-it's a bullet/barrel vibration thing,but you can get a rough idea-of trajectory and wind change-either from someone who actually shhots the load you do-or ball park by extrapolation from Commercial data-as below (sorry zero is all 200y) but it's better than nothing-comparatively...and noH&N data...24"/1in 16: drop/drift in 10 mph wind:

 

 

Hornady 35 grain V max @ 3100 BC.110 100y +2.8/2.9 200 0/13.5 300 17/36

 

S&B 45g SP @2346 BC.102 100y +6.4/4.8 200y 0/22.5 300y 34/54

 

Win 45 SP @2690 BC.130 100y +3.6/2.9 200y 0/13.5 300y 20/35

 

(the S&B load reminds just how catastrophic the 'old' Hornet was when both BC and velocity dropped).

For the 45 @2690,about another inch high at 100 will be ball parkish to duplicate-out to 200y-BUT test firing is the definitive check

 

gbal

[CliveWard]

Hi All,

 

Thanks for the info.

 

Looks promising then.

 

 

Cheers

 

 

 

 

 

Clive

[VarmLR]

I'd use a chrony and measure the average MV of both loads you want to compare, then using the manufacturer's BC and the measured MVs, you should get some pretty reasonable predictions which you can check out in the field.

[Chanonry]

You can have a stab on JBM.

 

Run one load through it.

 

Top left on the Output Data is "Elevation 4.151 Moa" or something of that ilk.

 

You then set up the next load on the input page.

 

In the third block of input data down. RH column, 3rd down is "Elevation" enter whatever the Elevation number from the first loads Output data was. In my example 4.151.

 

In the set of check boxes in the bottom section of inputs Uncheck the "Elevation Correction for Zero Range"

 

Run this.

 

Check in the second load's Output Data that "Elevation" is what you think it should be.

 

You now have a ballistic chart for your second load but with the zero set up for the first load.

 

That's the process. Does it work? Depends. Gbals point above re its all about barrel vibration etc rules. So you need to verify that the predicted dope matches up with reality. Sometimes it is close enough at the zero range certainly. Its still only a computer prediction with limited accuracy.

 

But if we are verifying dope why bother with the calc, just go shoot it and measure.

 

I have tried to work out offsets for different loads in the past and can't be bothered anymore. A bit like the switch barrel thing, I can't be bothered rezeroing all the time.

[CliveWard]

Hi Chanonry,

 

That's exactly what I was after. Thanks ever so much.

 

I did some range testing with WInchester 45 grain JHP factory ammunition and the JBM results are very similar.

 

Luckily the rifle has a very short heavy barrel so the windage for the different bullets tested so far is close enough for jazz.

 

I just need to wait for the H&N bullets to arrive in a few weeks time.

 

 

Cheers

 

 

 

 

 

Clive

[Tenex]

Can't see it. Even when changing from one batch of the same ammo' to another the POI can change vertically and horizontally due to speed and barrel harmonics.

Surely the best way is to simply shoot half a dozen rounds downrange and see where they go.

 

G

[Swarovski1]

I think I was told once if you have the same jump to the rifling with the different loads they will be very close.