Trouble Shoot Sudden POI Drop

[BoltBandit]

Took family and friends to the deer lease this weekend for the misses bday and enjoyed a weekend of 2a shenanigans and of course we eventually made it out to the power lines to do some long range shooting.

My buddy lined up on a hostage IPSC at 308 yards and nailed the baddy using 1.1Mils. He did this a few times.

Moved to 480 and nailed the waterline on an eight inch gong using 2.3Mils, again repeatable.

Lastly moved to the 805 yard target and nailed the water line using 5.3Mils w/ several fallow up shots.

Hell yeah, the Kestrel is ON POINT today!!!!

My turn....

1st shot, miss.... Same for the 2nd, 3rd, and 4th..... Odd. I made some adjustments to the wind thinking maybe there was something I wasn't seeing in the wind. Nothing. So I moved over to the giant 50 cal rated 24" gong and the rifle is low. The final elevation to hit waterline was 5.8Mils. As I worked my way back to the closer targets, my final solution was 2.4 Mils and 1.2Mils on the 480 yard and 308 yard gongs respectively.

Ok, maybe I have a soft shoulder during the recoil pulse? Maybe he's pulling into his shoulder super hard? Dunno....

Mind you, I'm the only long range guy here, so I'm acknowledging the potential for variations in technique.

Its the women and children's turn. Every damn one of them was ringing steel using 5.8 Mils.

To sum it up, the 5.8 elevation adjustment was the final adjustment, and its driving me crazy as to why. Especially when:
1. The Kestrel was spot on... who doesn't like that.
2. The rifle shot so consistently with the initial dope, and then shot consistently with the final dope.
3. There was a broad range of shooter experience levels, but still producing consistent results

So of course I'm trying to figure out why. Here is my gun, load and reloading process.

MPA BA w/ 26 Krieger barrel; 1:8 twist, w/ KGM suppressor; approx 1,000 rounds down the pipe. The rifle consistently shoot's 3/8" groups and 1/4" on a good day if I do my part.

6.5CM with Hornady ELD-M 140gn bullets w/ 42.2gn of H4350. Brass is Lapua small primer on its second firing. Primers are Winchester and something else, whatever I had on hand to be honest.

Also, I don't have any historical data on the ELD's with this barrel as I only shot Berger's until supply became an issue.

Reloading:

1. Decap and bump shoulder back .003" using a full length die. Brass is sprayed with Hornady case lube in a zip lock bag.
2. Brass is cleaned with a SS pin tumbler. Cases blown out with an air compressor and then air dried.
3. Normally I trim and chamfer the brass with a 3-way tool head on a drill press, but the Lapua brass wouldn't fit for some reason. I'm only guessing it's because the neck thickness is thicker than the Hornady brass I just retired? Not sure. Maybe there is build up on the tool head of some sort? Haven't had a chance to trouble shoot this. Regardless, this step was skipped and the brass was neither trimmed or chamfered.
4. Powder charged with 42.2gn H4350 using a RBCS Chargemaster light.
5. Base of bullets are dipped in RCBS dry case lube (with the little BB's) prior to seating .030" off the lands.
6. My only thought on fundamentals or shot mechanics rather, is I noticed the bipod was making a groove in the soft wet surface mud. Could the lack of friction at the feet of the bipod slipping in the mud casuse of POI shift?

So at this point, I'm trying to figure out what's going on here and can pinpoint a few potential areas of inconsistency. Again, keep in mind, there was a .5 shift in POI at 800 yards, which is 14.4" inches low. I did not chrono the rifle, but at the same time I can't imagine the bc suddenly changing in the middle of the day, so my assumption is the barrel slowed down. Here are a couple of thoughts.

1. Primer brand is inconsistent, but I wouldn't think this could be enough for a .5Mil drop in POI. Thoughts?
2. Is the chargemaster throwing consistent enough charges? All charges are confirmed at 42.2gn. Is there enough variation in charge weight to cause a .5Mil drop? How much change in velocity will occur with each .1gn of powder?
3. Could barrel temp have this effect? Could the bullet slow down as the barrel warms up?
4. Is there enough inconsistency in the application of the dry bullet lube to produce this amount of shift?
5. Could the lack of chamfer in the brass cause changes in chamber pressure? (if this is true, then why was the gun consistent in the beginning, and consistent after the POI shift?)
6. Could it be a dirty barrel? I don't remember the last time the barrel was cleaned, I need to check my logs, but could there have finally been enough fouling to drastically slow the bullet down?

Things I THINK I've ruled out:
1. Shooting fundamentals: Too many shooters of varying skill level and too consistent of results
2. Barrel life, only 1,000 rounds down the tube.

Let me know your thoughts!

 

[hlee]

Did your buddy shoot the rifle again after the apparent shift?

A difference of 0.1 mil at 300 yards is roughly 1” on the target, and at 480 it is less than 2”. That’s not going to cause a miss at those ranges. 0.5 mil is kind of a lot, even at 800 y, but my first inclination would be differences in shooter before some weird “shift in poi.” After that, I’d be looking at the rifle/scope- mostly the scope. It is uncommon for a scope to “die,” but it does happen. It’s even less common for a rifle to suddenly start printing in a new spot.

Unless you transitioned to a new lot of cartridges between you and your buddy shooting, the ammo would be my last concern.

 

[BoltBandit]

Did your buddy shoot the rifle again after the apparent shift?

A difference of 0.1 mil at 300 yards is roughly 1” on the target, and at 480 it is less than 2”. That’s not going to cause a miss at those ranges. 0.5 mil is kind of a lot, even at 800 y, but my first inclination would be differences in shooter before some weird “shift in poi.” After that, I’d be looking at the rifle/scope- mostly the scope. It is uncommon for a scope to “die,” but it does happen. It’s even less common for a rifle to suddenly start printing in a new spot.

Unless you transitioned to a new lot of cartridges between you and your buddy shooting, the ammo would be my last concern.

Yes, and 5.8 was still the proper dope. To add to that, my 13 daughter, 11 year old son, my wife, my buddy's wife, and his 18 year old and 14 year old shot and all rang steel at 800 with 5.8mils. Even I re-shot, still using 5.8 for confirmation, and re-shot at 5.3, and confirmed it was not enough elevation. So I had a bunch of people with almost zero shooting experience using 5.8. Grant it, the groups opened up a lot with the inexperienced shooters, but that's to be expected. So that doesn't make sense to me that its the shooter, but that's also why I'm asking.

The scope btw is a Zero Compromise ZC527, so pretty high end. I'm not sure what you mean when you say the scope could have "died". Everything was shooting consistent with the new POI. Is that possible with a faulty scope?

Same cartridges, all hand loads.

It's driving me nuts though, lol.

 

[kilizyrag]

I find that when I have similar discrepancies it turns out I input something wrong into the ballistic app.

 

[Long Range 338]

IMO you're going to have to go to the range and put the rifle on paper. Make sure your zero is good as well as your groups. Do a tracking test to make certain the scope is tracking properly. If everything is squared away that eliminates some of the variables. Most likely the scope or something different between shooters. Did you adjust the parallax? I've seen some variation between shooter settings. 0.5 mils is quite a bit of discrepancy however.

 

[BoltBandit]

IMO you're going to have to go to the range and put the rifle on paper. Make sure your zero is good as well as your groups. Do a tracking test to make certain the scope is tracking properly. If everything is squared away that eliminates some of the variables. Most likely the scope or something different between shooters. Did you adjust the parallax? I've seen some variation between shooter settings. 0.5 mils is quite a bit of discrepancy however.

Parallax was adjusted, and like you, that seems like a huge discrepancy for parallax.

 

[hlee]

I’m also going to throw out the idea of confirmation bias. Let’s just skip to the 800 yard target. You input all of the variables and the kestrel spits out a value. You give that to your buddy (who is a less experienced shooter) and he makes some hits. Everyone says “Bitchin’!” The rifle agrees with the kestrel so everything is “right.”

Now you (the experienced shooter) take over and all is not right with the world. Your shooting does not align with the kestrel. But, the kestrel is an infallible box that uses the wizardry of mathematics to create perfect solutions. Further experimentation shows that the rifle is incorrect by 0.5 mil at 800 yards. Why? It must be the rifle/scope/optic…

Here’s an alternative scenario…

Buddy is a somewhat inexperienced shooter. 1.1 v 1.2 mil doesn’t matter on steel at 300 yards. 2.3 v 2.4 mil doesn’t matter for steel at 480 either. He was going to hit regardless. A deviation of 0.5 mil should matter at 800, but he jerks some onto the target, and all is right with the world. But, as we know, all was not right. All along, the correct solution for 800y was 5.8 mil. After seeing you and the women and children connect using the correct solution, Buddy buckles down and makes hits with that dope too. The kestrel gave you a close, but incorrect, value.

Is 0.5 mil too much to expect to need to “true” out of a software derived solution at 800 yards? I’d also triple check all of my inputs. Something as trivial as scope height could be the culprit…

 

[Klemm]

Do you not have any previous dope?
Too compare?

 

[BoltBandit]

I’m also going to throw out the idea of confirmation bias. Let’s just skip to the 800 yard target. You input all of the variables and the kestrel spits out a value. You give that to your buddy (who is a less experienced shooter) and he makes some hits. Everyone says “Bitchin’!” The rifle agrees with the kestrel so everything is “right.”

Now you (the experienced shooter) take over and all is not right with the world. Your shooting does not align with the kestrel. But, the kestrel is an infallible box that uses the wizardry of mathematics to create perfect solutions. Further experimentation shows that the rifle is incorrect by 0.5 mil at 800 yards. Why? It must be the rifle/scope/optic…

Here’s an alternative scenario…

Buddy is a somewhat inexperienced shooter. 1.1 v 1.2 mil doesn’t matter on steel at 300 yards. 2.3 v 2.4 mil doesn’t matter for steel at 480 either. He was going to hit regardless. A deviation of 0.5 mil should matter at 800, but he jerks some onto the target, and all is right with the world. But, as we know, all was not right. All along, the correct solution for 800y was 5.8 mil. After seeing you and the women and children connect using the correct solution, Buddy buckles down and makes hits with that dope too. The kestrel gave you a close, but incorrect, value.

Is 0.5 mil too much to expect to need to “true” out of a software derived solution at 800 yards? I’d also triple check all of my inputs. Something as trivial as scope height could be the culprit…

You're not wrong, it's every good scientists achilles heel, lol. So yeah, that's certainly a possibility that can't be ignored. The kestrel is about as accurate as the bc value on the box of bullets! So I hear yah loud and clear. That .5 mils seemed like a lot of error to have to true out of the kestrel, but maybe there's something to my buddy's technique.

I've checked the inputs, they're solid. Same inputs I used with the previous load using Berger's minus bullet specific data, but always worth a triple check.

The more I keep thinking about it, I'm wondering if some rounds with Bergers were mixed in the box?

 

[BoltBandit]

Do you not have any previous dope?
Too compare?

Unfortunately I don't as its a new load after switching bullets.

 

[Slides]

Can easily have 1MOA or more elevation between shooters using the same rifle depending on loading bipod, pull into shoulder and weight on cheekpiece/into bag. I usually don't really lay into my cheek piece, if I do I get significant vertical shift, it's easy to see using electronic targets.