Short barrel wind deflection

[DangerRanger]

I built a 16.25” 6.5 creedmoor recently to hunt suppressed with. It’s mostly a 0-400tops rifle but I’ve been enjoying shooting it out past 600 as well.

I’ve been “struggling” with wind having a larger effect than my wind call more often than usual. I understand my kestrel is only reading a moment of time where I am, and I am looking at wind indicators that I can find downrange in the middle and at target.

I just feel like more often than before in my shooting life im seeing a wind call that turns out to be significantly higher than I called it.
Is it that my bullet is going slower than im used to out past 600 so what wind snags it out there has a greater divergence of the path than im used to? Is it that the bullet is going higher in the air/further in the air?

It’s not horrifically off. but it’s let’s say maybe I’ve got a .4mrad left hold from my solver, but I end up adding .2mils correction after spotting. Is this something I’m ignorant on concept wise or am I simply noticing I suck at calling wind

Load is 143gr @2430.

 

[ma smith]

A 16 inch rifle under 2,450 FPS is (too) slow for 140 class of bullets, and the exta TOF downrange is allowing the wind to act on the bullet for longer than "normal". Good rule of thumb is you need MIN 2550 FPS at MV for the 140s. One approach is to try the Berger 130 hybrid. They are lighter, slightly lower BC, but faster as a result and still fly very well.

 

[ShtrRdy]

What is the twist rate on your short barrel?

 

[DangerRanger]

What is the twist rate on your short barrel?

8 stainless tikka

 

[6.5SH]

I built a 16.25” 6.5 creedmoor recently to hunt suppressed with. It’s mostly a 0-400tops rifle but I’ve been enjoying shooting it out past 600 as well.

I’ve been “struggling” with wind having a larger effect than my wind call more often than usual. I understand my kestrel is only reading a moment of time where I am, and I am looking at wind indicators that I can find downrange in the middle and at target.

I just feel like more often than before in my shooting life im seeing a wind call that turns out to be significantly higher than I called it.
Is it that my bullet is going slower than im used to out past 600 so what wind snags it out there has a greater divergence of the path than im used to? Is it that the bullet is going higher in the air/further in the air?

It’s not horrifically off. but it’s let’s say maybe I’ve got a .4mrad left hold from my solver, but I end up adding .2mils correction after spotting. Is this something I’m ignorant on concept wise or am I simply noticing I suck at calling wind

Load is 143gr @2430.

Are your elevation predictions in the solver correct? If not those BC/speed errors affect the windage prediction as well.

If they are correct are you using the Kestrel in a vane mount? If not, do you have a piece of yarn or something else attached to get the direction to hold it into?

 

[DangerRanger]

A 16 inch rifle under 2450 FPS is likely is (too) slow for 140 class of bullets, and the exta TOF downrange is allowing the wind to act on the bullet for longer than "normal". Good rule of thumb is you need MIN 2550 FPS at MV for the 140s. One approach is to try the Berger 130 hybrid. They are lighter, slightly lower BC, but faster as a result and still fly very well.

Ok so maybe I’m not going insane lol

Are your elevation predictions in the solver correct? If not those BC/speed errors affect the windage prediction as well.

If they are correct are you using the Kestrel in a vane mount? If not, do you have a piece of yarn or something else attached to get the direction to hold it into?

Yes, but they would be. Mv is trued off drops. I guess I should get the magneto out, it just doesn’t like my can so it’s a pain. Direction is taken off feel combined with a tape on a pole at the firing line. I don’t find myself having the issue with my 26” but maybe the extra mv is just covering up my faults

 

[JerkyFreak]

The MV obtained with and without the can is close enough to make it worthwhile getting the Magneto out.

Guestimating velocity using drop only works if the bullet BC out your barrel is 100% correct.

 

[Kiba]

143s at 2430 out of an 8 twist might not be totally stabilized, and while they'll shoot good groups they might not be spinning fast enough to have complete stability to achieve the full rated BC which is why your real life drops and wind holds at longer ranges are greater than the software predicts if you're using the published BC.

An 8 twist is adequate for full stability for a 6.5mm 143gr bullet at the usual 2750ish fps range, but down at 2430fps the 8 twist may be on the border of starting to compromise the BC of the heavier 143s. Looking at some stability numbers, you'd need about a 7.5-7.7 twist to achieve comparable stability with the 143s at 2430 compared to an 8 twist at 2750 which is about the usual velocity range for 140s in a 26-28" barrel. If you look only at bullet rpm, an 8 twist at 2750 is spinning 247.5k rpm, and at 2430 fps you would need a 7.1 twist to get to 246.4k rpm.

Another vote for trying the 130s with your shorter barrel. The 130s will not only be faster, but because they're shorter and lighter they need less RPM to fully stabilize and have maximum BC-- so even though they won't be winning any speed contests out of your 16" barrel they will still be 100% stable out of an 8 twist and have full BC compared to the probably marginally stabilized 143s at 2430.

Edit for more info: Assuming you're currently running H4350 with the 143s at 2430fps, if you load to the same pressure with 130s you should get about 2540fps according to Quickload.

 

[DangerRanger]

Thanks guys!

Sounds like I should try 130s no matter what

 

[DangerRanger]

Simple. Call more wind.

I’m trying to figure out the why and if the why actually exists instead of getting ballistic solutions that are wrong and just doing something else.

Seems like that’s just creating a bad habit, and is going to muddy the waters when I have other rifles that I feel like I can trust the output on.

if it’s not a thing and I’m just sucking I want to know that too so I don’t train a crutch in that doesn’t exist irl