Weather accuracy

[Austin2512]

Not sure if this is the right thread to ask this but I was shooting today at 200 yards and dialed for my previous dope of .6 mils and was missing. I decided to dial .4 mile and was dead on. My previous dope I was shooting in 45 degree weather and today it was 82 degrees. Could the 37 degree difference really affect a .223 77 grain bullet at 200 yards by a difference between of .2 mils?

 

[Rudy Gonsior]

No, there’s a lot of other variables (non-weather) that are likely at play. Temperature at this distance is inconsequential.

 

[Austin2512]

No, there’s a lot of other variables (non-weather) that are likely at play. Temperature at this distance is inconsequential.

The only thing I could think of is the difference in bullet manufacturing or the fact I haven’t cleaned my rifle for 2 range trips now. If there’s any other variables I don’t know of please let me know

 

[Rudy Gonsior]

Question are as follows:

- What’s your optic set up?
- What’s your shooting platform? AR/Bolt?
- What’s your shooting support/position?
- Whats your barrel type?
- How many rounds did you confirm with and what’s your rate of fire?

 

[Austin2512]

Question are as follows:

- What’s your optic set up?
- What’s your shooting platform? AR/Bolt?
- What’s your shooting support/position?
- Whats your barrel type?
- How many rounds did you confirm with and what’s your rate of fire?

-vortex 2.5-10
-semi auto
-front bipod/ rear support bag
-Douglas barrel from CLE
-between the last two range trips I’ve shot about 50 rounds of the imi 77 grain stuff
- my rate of fire is about 1 round every 30 seconds maybe less

 

[Rudy Gonsior]

Ok so here’s what stands out to me as a good place to start base of the brief outline you gave and my experiences teach a couple thousand students over the last 10 years.

1. Make sure you’re firing statistically significant strings and series of fire to confirm POI/POA. 50 rounds over two trips (assuming you did more than bag away at just the 200y) isn’t much.

Shoot a 100y 5x5 without making any adjustments, getting up and breaking position between each 5 rounds, at your a sustained rate of fire and see what happens. Your 25 rounds should share an overlaying of POI in relationship to the POA or you may notice your POI isn’t actually where your POA was.

Additionally this could also highlight a possible “wandering” POI which is like related to improper fitting of the rifle to the shooter and/or poor fundamentals of marksmanship, particularly regarding body position and sight alignment.

A poorly fitted rifle or improper parallax can easily cause 0.1-0.3 shifts in your POI

2. Mechanical issues may be at play. Failure to properly mount, torque, locktite optics are very likely to cause issues at some point.

Lose bipods can also cause shift POI as well and the advent of lighter weight rails and flex under load can also cause POI shifts.

 

[JBoomhauer]

-vortex 2.5-10
-semi auto
-front bipod/ rear support bag
-Douglas barrel from CLE
-between the last two range trips I’ve shot about 50 rounds of the imi 77 grain stuff
- my rate of fire is about 1 round every 30 seconds maybe less

What size groups do you typically shoot?

Vortex has had to replace a 2.5-10 for me under warranty for a shifting zero.

And FYI it would take about 300fps to change poi by .2 at 200.

 

[Austin2512]

With that setup I’ve been hitting 1 MOA groups

 

[JBoomhauer]

Ok so here’s what stands out to me as a good place to start base of the brief outline you gave and my experiences teach a couple thousand students over the last 10 years.

1. Make sure you’re firing statistically significant strings and series of fire to confirm POI/POA. 50 rounds over two trips (assuming you did more than bag away at just the 200y) isn’t much.

Shoot a 100y 5x5 without making any adjustments, getting up and breaking position between each 5 rounds, at your a sustained rate of fire and see what happens. Your 25 rounds should share an overlaying of POI in relationship to the POA or you may notice your POI isn’t actually where your POA was.

Additionally this could also highlight a possible “wandering” POI which is like related to improper fitting of the rifle to the shooter and/or poor fundamentals of marksmanship, particularly regarding body position and sight alignment.

A poorly fitted rifle or improper parallax can easily cause 0.1-0.3 shifts in your POI

2. Mechanical issues may be at play. Failure to properly mount, torque, locktite optics are very likely to cause issues at some point.

Lose bipods can also cause shift POI as well and the advent of lighter weight rails and flex under load can also cause POI shifts.

Adding to Rudys point #1…

I would do exactly what Rudy said and keep track over a few more range trips.

To visualize, that is a 2” group centered 1.44” higher than another 2” group at 200y.

In this case all shots would impact a 3”x5” card at 200. Not sure what size target you were shooting at.

 

[Austin2512]

I was shooting at some of those orange clays, could have been my parallax and poor fundamentals on my part versus when I shot the first time and the fact that I use factory ammo

 

[Marine52]

As said above, atmospherics will not cause this shift in POI. However, if the ammo was left in the sun on a hot day, that would cause a jump in velocity.