load development and wind conditions

[turbohardtop]

I was out today to test 3 different loads for the 308. 175, 168 and 150 grain. This is the second time I was out for 175 and 168 grain ones. The weather was nice but a bit sporadic with wind. Wind was changing direction with gust around 10-15 mph. I noticed my groups for 175 was tight at 200 yards but still had 3 groups (out of 5)<=0.5 MOA. For 168 it opened up and was closer to 1MOA. For the 150 grain ones, the group was around 2.5" all at 200 yards. Is this expected? How do you deal with wind conditions when you go out to fine tune a load?

 

[targaflorio]

Re: load development and wind conditions

Worry about your vertical elevation. Wind moves the bullets horizontally.
Also a good reason to use a chronograph.
You can calculate the expected ballistics with a program like Shooter. Depends on the bullet weight, bc, and mv.
Going from a half moa to a moa group to 2.5" at 200 yds ain't the wind.

 

[Tripwire]

Re: load development and wind conditions

I'd love to find me some wind that only moves horizontally.......

OP....calm mornings/calm evenings.

Per load refinement anything else is pretty much pissing in the wind......

 

[turbohardtop]

Re: load development and wind conditions

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Tripwire</div><div class="ubbcode-body">I'd love to find me some wind that only moves horizontally.......

</div></div>
Tripwire, this would support my theory about the lighter weighted bullet being affected more, hence larger group. Last time I was out the 168 grain with 45 grain of varget had a single hole with 3 shot group. This time it was barely MOA.

 

[Tripwire]

Re: load development and wind conditions

Rest assured your theory was thunked out long ago.

Thus heavy high BC bullets being the choice for long range.......

 

[turbohardtop]

Re: load development and wind conditions

Thank you Tripwire. I am learning everyday.

 

[targaflorio]

Re: load development and wind conditions

I did a quick calc using Shooter. 175 SMKs doing 2700 fps mv and 168s doing 2750 call for the exact same windage at 200 yds: .4 mils and .6 mils for a full value wind at 10 mph and 15 mph respectively. I suggest you have other variables to deal with in your load development than just the wind.

 

[turbohardtop]

Re: load development and wind conditions

Thanks Targaflorio, if this is extrapolated to 1000 yards at the same conditions, what does it show for drift. Is the extrapolation fairly linear? I wonder why my 168 grain load did not do so well.

 

[targaflorio]

Re: load development and wind conditions

Not linear:
175s: 2.7 to 4.1 mils windage at 1k
168s: 3.2 to 4.8 mils

208 Amax doing 2850 mv : 1.8 to 2.6 mils (300 win)

 

[turbohardtop]

Re: load development and wind conditions

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: targaflorio</div><div class="ubbcode-body">I did a quick calc using Shooter. 175 SMKs doing 2700 fps mv and 168s doing 2750 call for the exact same windage at 200 yds: .4 mils and .6 mils for a full value wind at 10 mph and 15 mph respectively. I suggest you have other variables to deal with in your load development than just the wind. </div></div>

targa, so for .4 Mil at 100 yard = 1.44" and 2.16" respectively. This does coincide with my groupings right?

 

[targaflorio]

Re: load development and wind conditions

@ 200 yds, .4 mils = 2.88". .6 mils = 4.32"
My point was that the 168s and 175s call for the same dope (out to about 300 yds). Then very close through 600. So if your groups are different, it is because of your load, not because of the way the bullet performs in the wind. I started shooting 168s and dropped them completely, because once you are going past 700 yds, the 175 is a much better projectile. My go to load now is Amax 178s over 44.8 grs Varget doing 2700 fps good for 1/2 MOA at 600. I may try 208s next time... But for now, I'm working up my 300 win loads, which drop more than 100 inches less at 1000 than the 308.
Also remember, the less consistent you are feeding your barrell, the less well it will perform.
Good luck!