The other day, I was helping a friend with his new 6.5x47 rifle I helped him build and developed the load myself. This rifle will shoot .3 moa with the 130 VLD running 2873 fps. Very low ES; like 15 fps. Back on the 4th of July, I was testing the rifle/load out at 1089 yds on a rock approximately shoe box sized, up on a cliff. Zero wind and about 70 def F. I kept hitting this rock over and over and over. Now, two days back, I had my friend out, I was shooting at the same rock and still kept hitting it. We decided to stretch it a bit further to a suit case size rock (I think. Not climbing the cliff to measure it) sitting at 1341 yds.
11.9 up angle
68 deg F
Humidity: I always run 30% here in Utah unless it's raining.
zero side wind
Sight ht of 1.9" with NF 5.5-22 sitting on top of the Stiller action.
Both Gunwerks G7 and Shooter give me 41.25 moa. I'm using the G7 BC of .282. Yet, I'm hitting above the rock, approx 1 full moa high.
I get home, figure I need to try and use the Coriolis Effect feature of Shooter.
Azmuth of about 38 deg
Coriolis changes it to 41.9 which is in the wrong direction. I needed to come down to about 40.25 to hit the rock. I was watching for updrafts and once in a while catch a spider web or cotton wood, barely up drafting. No way to measure that nor to enter that in to Shooter! Or is there?
Thanks for any input.
Last edited by Alan Griffith; 07-21-2013 at 11:22 AM.
Your problem is common. And one I am working on diligently.
1: Lets start with a basic problem that has caused many grief. Actual scope tracking. Your scope may actually be moving your point of impact, lets say, 1.05 moa instead of 1.0 moa. This will appear to be a larger issue as distance increases. This is adjustable in shooter and Bryans AB program. Take your log book data and play with it to see if you can get on at several distances by adjusting this.
2: Angle of target face and angle bullet is descending. What looks like 1 moa or even measures 1 moa through a reticle might not be when the angles are added to the equation. Retest at both distances using a 90* target surface like a steel target or a rock wall. To get accurate drop data.
3: Up draft. Very common when we shoot long. We are usually shooting up. I find thermal and other winds are commonly present with up hill slopes. Do this test or use it to help with a first round dial up. To the best of your ability guess the wind going up where the target is. Look at the wind angle and how it will be contacting the angle of the descending incoming bullet. Many times this is a full value effect.
Enter the wind speed in your program as a full value cross wind and get the drift it will give in moa. Then use that number as to what you need to subtract from your dial up. Notice how little of an updraft it will take to lift you 1 or 2 moa.
Wow! Now that's a few great answers. Now, all I have to do start going through them.
Thank you VERY much!
1. Could a NF NXS really be off? Even a tiny sketch?
2. The rock I was shooting was sitting on a tiny ledge; cliff face, so doubt this will be an issue.
3. At a distance of 1341 yds, Shooter says a 1 or 2 mph full value wind would move me .5 to 1.3 moa. So, if I apply that value from below, the slightly up ward moving cottonwoods and/or spider webs are a great tell tale sign that that is likely the issue. As I think about it, the 1089 yd hits were flying over pretty much empty space until the last hundred yards yet the 1341 yd misses were flying more along the canyon wall for maybe 400-500 yds of up ward angling slopes and cliffs.
1: you bet!! We do not live in a perfect world. These differences in tracking may be so slight you cant detect them at 100 yards. Just for an example, a correction of 1.0 (1.047") compared to 1.04 (1.088") at100 yards is a difference of .041" that is 41 thousands of an inch. Hard to detect at 100 yards no mater what method used. But at 1300 yards the difference is .545 moa.
2: as long as you had a vertical target surface for both shots you are probably safe to use the data. But there is no better way to get accurate data than a vertical steel plate or paper target you can walk up to with a tape measure.
3: Remember to switch off the spin drift when you are using windage drift to give a correction for an up lift.