140 Amax at 1k and further, calculator is off

[MrGreg]

I got a chance to shoot past 600 yards for the first time this weekend, and I've found my calculations are incorrect past 900 yards. I was able to get good dope from 400 to 1200 at basically 100 yard increments.

I'm shooting factory 140 Amax (all the same lot, groups .5 MOA or better under 600 yards) from a 6.5 creedmoor, and using the Shooter app to calculate my dial-ups. Currently using a G1 of .585. 22" 1:8.5 twist Bartlein barrel.

With a MV of 2700 (estimated, not confirmed with a chrono) the calculations are dead on from 400 to 900 yards.

But at 1000, it's telling me to come up 1.5 MOA too much.
At 1130, it's telling me to come up 2.75 MOA too much.
At 1200, it's telling me to come up 2.25 MOA too much.

If I use a MV calculation tool to try to find a MV that fits the data better, I get 2747.5 fps. Using that, the numbers for 1000-1200 are much closer, but now I'm off by at least 5% for everything 900 yards and closer. See G1 attached pic for full numbers.

Then I tried using G7 of .299 (Litz) and see if I can find a MV that fits the known dope. With 2710 fps, I'm mostly within about 3.5% (chart attached).

The numbers are so accurate from 900 and closer with the G1, I don't want to screw those up in order to fix 1000+, if I can help it.

I was shooting at 4200 ft elevation, 65F, DA of 5800, 24% humidity, station pressure of 25.66.

Does anybody have a suggestion how to make the numbers match reality at 1k+ without messing them up for 900 and closer?

This is all somewhat academic, as once I shoot this factory ammo up, I'm going to start loading 140 hybrids, but I'd still like to figure out what's wrong. Any suggestions appreciated.

 

[WaltHer]

Just out of curiosity you might try a different ballistic solver like AB or JBM. I get subtle differances between AB and Horus. Im hoping that my recently "trued" AB profile will provide a better firing solutions. The truing feature on AB caused less distortion at closer, confirmed distances than simply adjusting the MV on the horus. I went from being .25 low @ 1520 to 2-3 low at 1953 all while the projo is still supersonic. Keep us updated.

 

[oneshot.onehit]

Did you run a calibration test on your scope? Not a box test

Cheers

 

[Frank Green]

Use a good chronograph or two and see what you get for velocity. That's the first thing I do.

You list the altitude etc....but did you figure in sight height in relation to the bore etc....? It's another variable.

With that being said did the conditions change thru out the day while you were shooting? Like when you started shooting the temperature was 65 degrees but later in the day is when I assume you shot the longer distances did the temperature go up to say 80 degrees?

Just curious because these changes can make your data cards be off from what you think. Your temperature changes and can effect your velocity of your ammo etc...will effect your come ups.

My range data cards for my F-Class gun were right on the money at 300 and 500 yards but when I got to the 600 yard line that one day my gun was 3/8 moa to high at 600. The gun was shooting flatter! When I got home I changed the data from what the temp and humidity was when I started shooting to data when I got to the 600 yard line. With the temp going from 65/70 degrees up to 95 degrees when I got to the line and I changed the velocity of my ammo up another 30fps the numbers came in dead on.

That's another reason I try to keep my ammo out of the sun etc....temps go up/ammo gets hotter from laying in the sun etc....can give you changes in your velocity of the ammo.

Later, Frank
Bartlein Barrels

 

[Rob01]

I can tell you that G1 BC is on. I used it in JBM for a match a few weeks back and it was dead on at 1050 yards and at 1000 I was ringing a 12" piece of steel over and over like it was my job.

Some things to do. Check your velocity on a chrono. Back calculating is fine but there are variables that will give you bad velocity numbers that way.

Run a tracking test on your scope out to atleast 35-40 MOA. This is the biggest variable that can mess with your back figuring velocity. If the scope isn't tracking dead on then you won't have a true velocity. Scopes can track fine for 10-15 MOA and then go bad. That's why small 5-10 MOA box tests are useless. Run up the elevation and check it on a proper tracking test.

Make sure all your data was properly put into the calculator. Garbage in gets garbage out in these calculators. Also try another calulator like JBM.

Also what was the area like you were shooting in? If it was hilly and target was on a hillside then you could possibly have some updrafts effecting the bullet. Just something else to think about.

If you log that data you have now in a data book then you have your come ups now for that area and conditions. You should be doing that.

 

[MrGreg]

Did you run a calibration test on your scope? Not a box test

I have not yet done that. It is a NF ATACR MOAR.

 

[MrGreg]

but did you figure in sight height in relation to the bore etc....? It's another variable.

Sight height is 2.396"

With that being said did the conditions change thru out the day while you were shooting? Like when you started shooting the temperature was 65 degrees but later in the day is when I assume you shot the longer distances did the temperature go up to say 80 degrees?

It did warm up somewhat, but I was measuring that before each new target. The column labeled "field calc" was done using the atmo at the time. The conditions I listed in my original post were somewhat of an average. I'm not taking into account powder temp variations, though. I did keep my ammo out of the sun and in my backpack, but it could have warmed up a bit throughout the day.

 

[MrGreg]

I can tell you that G1 BC is on. I used it in JBM for a match a few weeks back and it was dead on at 1050 yards and at 1000 I was ringing a 12" piece of steel over and over like it was my job.

Yeah, I'm assuming the problem is on my end, not Litz's

Some things to do. Check your velocity on a chrono. Back calculating is fine but there are variables that will give you bad velocity numbers that way.

I need to get one. I'm kinda waiting for the magnetospeed classic to come out.

Run a tracking test on your scope out to atleast 35-40 MOA. This is the biggest variable that can mess with your back figuring velocity. If the scope isn't tracking dead on then you won't have a true velocity. Scopes can track fine for 10-15 MOA and then go bad. That's why small 5-10 MOA box tests are useless. Run up the elevation and check it on a proper tracking test.

Next time I shoot, that's the first thing I'll do.

Make sure all your data was properly put into the calculator. Garbage in gets garbage out in these calculators. Also try another calulator like JBM.

JBM pretty much agrees with Shooter, so again, it's probably an error on my end.

Also what was the area like you were shooting in? If it was hilly and target was on a hillside then you could possibly have some updrafts effecting the bullet. Just something else to think about.

900 yards was the base of a hill, and the 1000, 1130, and 1200 were on their way up the hill. I don't know the angle of incline of the shots, but I'm going to try to determine that. Updrafts are certainly possible.

If you log that data you have now in a data book then you have your come ups now for that area and conditions. You should be doing that.

Yes, I kept a ton of notes. It's from those that I'm trying to figure out what happened.

Thanks for the suggestions, everyone.

 

[MrGreg]

Based on elevations, I believe I was shooting at a slight incline:

900 yds - 1.4 degrees
1000 yds - 1.8 degrees
1130 yds - 2.8 degrees
1200 yds - 3.4 degrees

But it appears this isn't enough to account for the full discrepancy. It looks like these inclines make almost no difference at all.

 

[oneshot.onehit]

I have not yet done that. It is a NF ATACR MOAR.

If your serious in shooting ELR then you should take time in calibrating your scope, yes it is a ATACR but we don't assume everything is correct. We take the time to test whatever it may be, be it a Vortex Razor or a Schmitty, it goes through the test.


Cheers

 

[MrGreg]

If your serious in shooting ELR then you should take time in calibrating your scope, yes it is a ATACR but we don't assume everything is correct. We take the time to test whatever it may be, be it a Vortex Razor or a Schmitty, it goes through the test.

I completely agree. I didn't mean to imply otherwise. That's how I figured out my VX-3 on my .223 is adjusted in IPHY, not MOA.

I've also ordered a Magnetospeed V3 today, so I can nail down velocity and remove that as a variable.

 

[8541recon]

I completely agree. I didn't mean to imply otherwise. That's how I figured out my VX-3 on my .223 is adjusted in IPHY, not MOA.

I've also ordered a Magnetospeed V3 today, so I can nail down velocity and remove that as a variable.

Good call on the magnetospeed, but something else is up I think. If you are on out to 9 and it falls off (I am assuming you are on POA POI, not "somewhere on an echo"), then I would tend to agree with the tracking problem. Have you tried to dial to 900 and then hold out further? Tracking target would be best way to tell, but it can also be expensive depending on how it is done and how precise you want it.

If you were talking subsonic ranges and using a G1, then I would say you might need to adjust for a subsonic G1, but you should be good well past 900. I am interested to see what you come up with.

 

[MrGreg]

I'll do a tracking test and post the results. Thanks for all the suggestions, everyone.

 

[MrGreg]

I wasn't able to do a scope tracking test yet (apparently my main range doesn't like targets that extends beyond the holders, even if it's below).

But I was able to measure velocity with my shiny new magnetospeed v3.

Turns out I was getting 2760 (with an es of like 60!). And the other interesting piece of information... my zero is somehow .6 MOA low.

Correcting for both of those factors, my calculated drops are now within about .4 MOA (or less) of measured actual dope for all tested distances.

I'll still do a tracking test when I can, but this makes me feel better to have the numbers match up.

Thanks for the suggestions, everyone.

 

[PS-G1_Sniper]

Thanks for the update, Greg.
I shoot 140 amax out to 1200-1250 on a modern action Swede and feel the .299 G7 matches my drop more accurately past 600 yards as well.

 

[MrGreg]

As a further update, last weekend I was finally able to do a scope tracking test. Out to 40 MOA (in 10 MOA increments), my ATACR is accurate within 1.5%, which is within my range of acceptable tolerance... and simple to correct for in Shooter.