Range Report Weird ballistics from todays shooting session.

Alpine 338

Lumberjack
Full Member
Minuteman
Jun 26, 2010
2,596
1,794
NW Colorado
A few days ago I mounted my new S&B 5-25x56 on my TRG-42 in 338LM. Friday afternoon I sighted in the new scope at my backyard 100-yard range. One round after boresight, adjusted, then one round for minor adjustment, then three rounds for confirmation.


Today, I set up a target at 300-meters and dialed in 1-mil of elevation dope (JBM Ballistics called for 1.1-mils). Had a tail wind at nearly 6-O'clock averaging 9 to 10-mph. So I figured I didn't need the extra 0.1-mil dialed in as the wind would carry the bullet. I then shot a 5-round string. Other than the wind, I had some heat mirage and couldn't get a pefectly crisp picture while adjusting the parallax.

The 5-round group had a vertical spread of about 3-inched, and a horizontal spread of about 1.5-inches. The group was centered almost perfect on the vertical centerline, but the weired thing it was a little over 3.5-inches low, or 1-mil low of the horizontal centerline.

The only thing I can figure is that the wind was pushing the rounds down because my shooting position was on a rise or elevated position, the the 300-meters to the target was a big depression, with the target on a hillside at roughly the same elevation that I was shooting from.

We then engaged steel at 930-yards, or 850-meters and the wind had moved to a crosswind at about a 45-deg angle from the rear. With the remaining 9-rounds I only hit that 18x20-inch plate once, most of the rounds went just over the top of the steel because of the wind kept carrying the bullets.

Anyone else expeience the wind pushing their bullets down, or was I experiencing the effects of mirage?
 
Re: Weird ballistics from todays shooting session.

FYI Was shooting factory Black Hills with 250-gr SMK, temp was around 73-deg F, and if I where to guess, the humidity was less than 20%. Pressure was on the rise.
 
Re: Weird ballistics from todays shooting session.

Can't blame the ammo since the rifle was laser beam accurate with the same ammo and previous Nightforce scope. I have a severial hundred rounds of the 250-gr stuff, bought it when I had my other TRG with 1/12 barrel. The current TRG is a 1/10, and the only ammo I will buy or reload in the future will be 300-gr Scenars, unless I stumble across some RAUG 250-gr AP at a fair price just to try out to see what it will do on AR500.
 
Re: Weird ballistics from todays shooting session.

I thought mirage over most surfaces tended to displace the image upwards to make the rounds hit high...

My Dad has reported vertical crosswind effects at an old range at Pendleton, where the big end of the firing line extended into what used to be air space in a large gully. The line, of course, was built up as a level berm, and was more than 20 feet above the rest of the original grade. IIRC, it was good for 1-1.5 MOA with .30-06 at 300.

Running the ballistics software will show that the point of impact effects of headwinds and tailwinds is exactly the same as fudging muzzle velocity by the same number of fps.

I've never seen any real scholarly discussions or results of experimentation on both head/tail winds and vertical components of crosswinds, though. You should apply to DARPA or someplace for a federal research grant.