Need help figuring out discrepancies

[Alan Griffith]

My best friend, his friend and I are heading Montana on Thursday for a week long elk/deer hunt. They both shoot nearly identical rifles in 6.5x284 with the 140 VLD running 3050 and 3075 respectively; same powder/primer loads too.

Last week, they both checked their 200 yd zeros and 300 yd impacts. These rifles are exceedingly accurate (Jon Beanland). Today, on a windless day, they were shooting at 550 yds. Shooter ap was saying 7.75 moa for the first and a skootch less for the 2nd rifle. Seems they both needed 1.5 moa more (9.25 moa) to hit @ 550 yds. On the phone I went over their Shooter rifle/load and field conditions input and we just couldn't figure out what was off. I even duplicated my buds data on my Shooter and came up the with same as theirs.

In the interest of time, having run dry of N560, their powder, and a shortage of loaded ammo, any ideas on what to tweak to get things married up? Maybe tweak bc, vel or zero on the ap? For some reason my bud was using .595 bc for the 140 VLD instead of the .612 it should have been. Don't think that much diff in bc would equate to a 1.5 moa diff @ 550 yds; do you?

Alan

 

[SBruce]

My first thoughts would be velocity.......are you all sure you're getting 3050-3075'/sec.?? BC doesn't make that much difference at 550.

2nd consideration would be shooting conditions, mirage ect. I've personally seen (more than once) up to 1 moa variance based on a combination of shooting rest, sun angle and mirage. I've see nearly 1 MOA at 300 and also seen it at 1000. Went back to original conditions a few days later and had predictable results. Not saying this is the case in their case, but it does happen. Seen >1/2 MOA vertical at 300 yds just off ground mirage alone!!

My program says you'd have to be around 2750'/sec. to need 9.25 MOA at 550.

3rd consideration would be scope click values. Have they done the click tests.?
IME most scopes dont actually move the POI the advertised amount, and that makes a huge difference when dialing corrections.

If they had more ammo, I'd say shoot again through the chono and shoot again at 200, 400, and 500/550. Also shoot a click test. Do this under favorable conditions and make the print out match your real world results.

 

[SBruce]

Alan,

Worst case scenario, considering low ammo count; re shoot drops at 300, 400 and 500. Then simply use the MOA or MiL reticle to holdover the needed amounts, and then shoot at game only under calm conditions. We were pretty handily shooting to 600 yds long before ballistic programs and "speed dial" scopes came about by doing only that.

Good luck on the hunt.

 

[tom m.]

You MAY have entered your station pressure but not checked the box?

 

[steelshooter]

I have nothing but trouble with long range shooting. I know I can produce good loads and shoot good groups at 100yds, but beyond 500yds it all falls apart.
I've read every article and seem to know it all in theory but just can't put it together in practice. I am not detered though, and am still persevering however frustrating it gets.
My Shooter program outputs never work for me and I always have to make adjustments, from one day to the next.
Some people are born arsey and everything "just works" with anything they do. I am the exact opposite.

 

[Alan Griffith]

Some good replies. Thanks.

Questions:

1. Buddy called Berger. They chastised him for using G1 instead of G7 BC's. We both recomputed to G7 and it only changed dope .1 moa. What gives?

2. It was in the 70's the am they shot their rifles @ 550 yds. It was pretty windless, so probably a boil. When shooting in mirage, is the mirage going to cause one to shoot/hit high or low?

Alan

 

[SBruce]

Some good replies. Thanks.

Questions:

1. Buddy called Berger. They chastised him for using G1 instead of G7 BC's. We both recomputed to G7 and it only changed dope .1 moa. What gives?

2. It was in the 70's the am they shot their rifles @ 550 yds. It was pretty windless, so probably a boil. When shooting in mirage, is the mirage going to cause one to shoot/hit high or low?

Alan

Alan,

G1 vs G7 simply doesn't matter much at the distances we're talking about (as you discovered) That stuff is for the ELR guys, who are obviously in a league of their own, most of us hunters don't shoot/practice enough to have a prayer of making a cold bore shot at over 1/2 mile under field conditions most of the time. I am using G1 for the 140 VLD in a 6.5-284, confirming and re-confirming drops to 800 yds a couple times now and everything is working out just fine. Not to mention, the Exbal PC version that I am using has alot of glitches when it comes to trying to use G7's.

Mirage.............HMMM, most wont admit that it matters, except the guys that shoot benchrest competition. These guys have guns and loads that are capable (under the best conditions) of shooting 1" groups at 600 yds when everything is right. Not just the occasional fluke group but somewhat repeatable. Ask any world class benchrester; 100-300, 600 or 1000 yd, and they'll say we never want to shoot on a boil. They'll also say that sun angle affects the image in our scopes and POI changes as the sun angle changes. Hell, a good friend of mine shoots rimfire comp and he'd much prefer an "honest" wind of 5 mph over a dead calm boiling condition. Because "we just cant predict where our vertical will end up".

As for Mirage, I am working up a custom 6.5-284 and during drop confirmation; I shot at 300 yds - 3 times - 3 different days - Once off the bench with an elevated target (both bench and target ~ 3' off the ground) and once off the bipod prone with the target 12" above the ground, and once prone off the bipod with the target elevated about 3' above the ground.

The prone position with the target just off the ground had terrible mirage. The 3" aiming dot was dancing around up to 3/4 MOA in any givin direction. The target was fuzzy no matter how I adjusted the SF knob. That group was ~2" low of where the other two groups printed under different conditions (mirage didn't appear to be nearly as bad when the target or the gun was elevated off the ground). Long story short, my non-mirage POI matched the ballistic programs, the mirage induced POI wouldn't match. I've confirmed out to 800 yds, and the mirage induced 300 yd POI was obviously a fluke. As you've said, the guns are accurate, so something has gotta explain it. Mirage is the only thing I could come up with in my experiences.

If I'd have used the mirage induce POI to tweak my velocities or SI distance, I'd never have hit this mark at 700 without further adjustments, as it was; I dialed what the program said and my errors were wind related only.

 

[Joe King]

Sighted in at later in the day say late evening, then shoot at noon, Mirage, reading 500yrd drop and shooting at 550 (it's an easy mistake to make) If something like this happened I can see it happening pretty easy or even being worse. I bet your discrepancy is in the details somewhere though.