Need help to "true" my chart...or should I bother?

[bdg848]

Hello all,

I have set my maximum hunting distance as 600 yards based on my group size but I need help with a drop chart. I don't have a chronograph so I guessed a velocity for the sterlok app, shot at 300 and 600 with the suggested drop, and was intending to adjust velocity from there to get close adjustments at both distances. It was telling me 1.2 mil at 300 and 3.8 at 600. My actual results are 1.6 and 4.1 Mils. I cannot adjust the velocity and get it to give me a close number on one without throwing the other off significantly. To get 300 to match, the velocity must be 2500fps and that makes 600 yard drop 4.8 mils... .7 too much. To get 600 to match, I'm at 2675 fps and that makes 300yd 1.3 .3 too little drop.

I'm completely new to this (ballistics, not the fundamentals of marksmanship) so I'm not sure what to do next. I can just shoot off of my known drop but my hunting will be done about 4000 ft in elevation higher so I was really hoping to be able to simply adjust elevation in the app when I got there and then quickly confirm it. Now I won't know to even trust my known data with the elevation change....any advice?

*edit* After messing with the altitude, the app didn't change any of the data with an elevation difference from 500' to 4000'. When I set elevation to sea level it changed the data by about a tenth of an inch...So I guess at 600 yards I can ignore the elevation change?? Does that seem right?

 

[Rob5589]

The most accurate way is to shoot at the intended distance with the same environmentals. Of course that isn't usually possible. In that case I will use my base set up and enter it into an app (I use Applied Ballistics) at various elevations and temps. That should give a good baseline to work off. I generally don't worry about it too much about it unless I see a ~ 5k foot increase and/or significant temp changes.

 

[Zane Shepherd]

Fwiw, I've ran a lot of apps, applied ballistics with cdm drag models is now my go to.

Just ran ballistics on my 338 edge. 4000' of elevation is roughly 4 points of barometric pressure difference. When I run ballistics for this the difference from baro pressure alone is 0.1 mil at 600. Thats roughly 2.16".

If you can't make the actual field results match your app numbers by adjusting velocity, try adjusting the bc.

Also, here in Oregon when I shoot long range, it is often across canyons. Canyons can have up or down drafts which will mess with your numbers.

Mirage is another thing that can yield poor numbers. When I'm verifying data I do it right at first light, setting targets up in the dark,, which will generally yield the best shooting conditions. In the past I've done it in the middle of the day, in lots of sun, and had less meaningful results.

Hope this helps.

 

[Wrench]

Have you tall target tested? You may have a scope with values that are not exactly as described.

Here's how I handle your situation.

Tall target test to get values. Shoot 100' for zero and as far as I can....to 600 for velocity validation. 700-infinty for bc validation.

If the gun groups well (moa or better) and the scope tracks well......and the velocity guess can be dialed in from 3-600.....the only thing left is minor bc variation due to rifle or environmental.

You must realize that the info you feed is responsible for what it produces. It scope height is 1.02....feed it that. If the info is right it will be closer than you're capable of.

 

[Wrench]

Most programs have a feature where you can take the called dope and compare to the actual strike location and use that for velocity correction.

 

[bdg848]

Fwiw, I've ran a lot of apps, applied ballistics with cdm drag models is now my go to.

Just ran ballistics on my 338 edge. 4000' of elevation is roughly 4 points of barometric pressure difference. When I run ballistics for this the difference from baro pressure alone is 0.1 mil at 600. Thats roughly 2.16".

If you can't make the actual field results match your app numbers by adjusting velocity, try adjusting the bc.

Also, here in Oregon when I shoot long range, it is often across canyons. Canyons can have up or down drafts which will mess with your numbers.

Mirage is another thing that can yield poor numbers. When I'm verifying data I do it right at first light, setting targets up in the dark,, which will generally yield the best shooting conditions. In the past I've done it in the middle of the day, in lots of sun, and had less meaningful results.

Hope this helps.

Now that you mention mirage, It was midday and there was definitely a good bit of heat boiling up in the glass. I will have to try again first thing in the morning and see if my POI changes.

 

[wind gypsy]

What load are you shooting, barrel length? The actual numbers you’re getting seem very unlikely which is probably why you can’t get the app to line up. I’d guess one of the following is at play:
1. Poor zero at 100
2. Scope doesn’t track accurately
3. Crazy down drafts after the first couple hundred yards?

 

[bdg848]

Its a 270win 150gr Nosler ABLR. My wife's grandpa helped me load them, I dont have the exact load with me. My 100 yard zero is solid and I doubt there is a downdraft issue for me...Eastern Iowa doesn't have the terrain for that haha. My scop is an Athlon Midas Tac.

 

[pyrotechnic]

Read this. It sounds like you have a combination of factors screwing up your results.
With a somewhat accurate BC, you should be able to get a close match out to 600yds by just adjusting muzzle velocity......IF the other inputs are correct.

A primer on point mass solvers (ballistic calculators)

I’m pretty new to this forum, I lurked for a while before I joined and the membership here has guided a lot of purchases regarding tents, sleeping bags, pads, clothing, and binoculars. Not to mention hours upon hours of entertainment reading threads on hunting and getting to live and learn...

www.rokslide.com

 

[wildwilderness]

Easy answer borrow a chrono. No way it should be around 2500 fps though, Too slow.

With all calculations garbage in equals garbage out. Double check everything, and do a track test on your scope.

 

[BRTreedogs]

So I have been having this same problem. On 2 rifles and it was suggested that I my scopes may be off. After seeing a couple other questions answered on here I have come up with a couple factors.
Aerodynamic jump. One direction it pushes the bullet up. The other down. I always have just left my app with 10 mph wind at 90 degrees because I didn't know it mattered at all on the dial up.

The 100 yard zero. I've just been using my range finder. There usually plusnor minus 1 yard.

Need to check with a 300' tape. From the turret of the scope as thats where the adjustment is made, to the target.

 

[pyrotechnic]

Aerodynamic jump is not going to result in a 0.7 mil difference between theoretical vs actual results.
The OP needs to go through his inputs one by one and make sure he understands what they are and that they are correct. Make sure your not using a g7 BC number if your program is referencing a g1 model.

 

[Vandy321]

Borrow a chrono, download hornady 4dof, ensure all data is spot on (including zero angle and sight height) adjust form factor as req'd for trueing.

Frank from SH has a podcast on the 4dof app as well as a bunch of posts about it on the hide.

Not implying you're not, but be confident you and your rifle are capable of shooting well enough to know its the data and not the shooter, .3 mil in vertical at 600 yards (your 3.8 mil vs 4.1 mil) is only ~6.5" total, if your rifle is a 1 MOA rifle, that could be as good as you get.

Worst case, use your real world data at 600 yards, true that with whatever MV makes sense and don't overthink it.

 

[pyrotechnic]

Re-reading your OP I would definitely double check your zero. You have a 0.3 mil error at 300 and a 0.4 mil error at 600.
Assuming everything else is correct my best guess you are low on your 100yd zero by around 0.3 mil and a slight tweak to your initial velocity guess would get everything to line up perfectly.

As mentioned a 0.3 mil error is right around 1" at 100yds, 3" at 300 yds, and 6" at 600. Are you repeatable enough to resolve that at the further distances? Are you shooting steel or putting groups on paper?

 

[Wrench]

Use .317 (g7) for a bc. My mv is 2941fps....that with rl26. I have proven this to 1400 in my 270 with that bullet.

I suggest you really scrutinize your 100yd groups. The LRAB is a PRICK about neck tension. If you call nosler and talk to the ballisticians they will confirm.

For me to get acceptable accuracy with the lrab in a rifle that has ripped countless one hole groups, I had to run a lee factory crimp die and a fair jump.

There is something about the material they used in that bullet that causes it to slug up inconsistently....I forget the whole story, but nosler was very open about it when I called them. They'll suggest faster powders like 4350/4831 which I had good luck with as well.

 

[bdg848]

Re-reading your OP I would definitely double check your zero. You have a 0.3 mil error at 300 and a 0.4 mil error at 600.
Assuming everything else is correct my best guess you are low on your 100yd zero by around 0.3 mil and a slight tweak to your initial velocity guess would get everything to line up perfectly.

As mentioned a 0.3 mil error is right around 1" at 100yds, 3" at 300 yds, and 6" at 600. Are you repeatable enough to resolve that at the further distances? Are you shooting steel or putting groups on paper?

Yeah, I had .9 100 yard zero, 2.3 inches at 300, and 4 inches at 600 all on paper. Each a 3 round group. I'm good enough at pulling a trigger but don't know anything about the science and math...kind of like a trained monkey haha. I thought my zero was right on but I don't have that target to confirm it wasn't slightly low. I will have to go out first thing tomorrow morning and try again.

Other people have mentioned borrowing a chronograph; I have tried to find one, believe me.

 

[Vandy321]

Yeah, I had .9 100 yard zero, 2.3 inches at 300, and 4 inches at 600 all on paper. Each a 3 round group. I'm good enough at pulling a trigger but don't know anything about the science and math...kind of like a trained monkey haha. I thought my zero was right on but I don't have that target to confirm it wasn't slightly low. I will have to go out first thing tomorrow morning and try again.

Other people have mentioned borrowing a chronograph; I have tried to find one, believe me.

Sounds like you have roughly a 1 moa rifle. I think you're spinning your wheels worrying about a few tens of mil at 600 yards. If that rifle was shooting 1/4 MOA, you could knats-ass it a bit more.

I'd grab real world drop at 600 from the center of multiple 3 shot groups. plug that in the app and use whatever speed the app says, call it good.

 

[wind gypsy]

Yeah, I had .9 100 yard zero, 2.3 inches at 300, and 4 inches at 600 all on paper. Each a 3 round group. I'm good enough at pulling a trigger but don't know anything about the science and math...kind of like a trained monkey haha. I thought my zero was right on but I don't have that target to confirm it wasn't slightly low. I will have to go out first thing tomorrow morning and try again.

Other people have mentioned borrowing a chronograph; I have tried to find one, believe me.

I'd confirm zero with at least 5 shots if they aren't all stacking on top of one another, more is better. At almost 1 moa for a 3 shot group, there is opportunity to have some error in where your actual zero is.

I know a higher BC was posted above in this thread but I wonder if you aren't getting full stability with that bullet in your rifle. This could explain some delta at 600 but the real oddball in your results is the 300 yard data where BC has little impact. It's hard to load a 270 slow enough to need 1.6 mils up from a 100 yard zero at 300.

An old thread with Litz tested BC from the LRAB.

Nosler LR Accubonds: BC testing results

I've been able to get my hands on 4 out of the 7 LR Accubonds; everything up thru 7mm 168 grain. The following summarizes my BC testing of these bullets. One of the big questions is: are the BC's actually as high as they're claimed/advertised to be? See the chart below for a summary of my...

www.longrangehunting.com

 

[MidGAHunter]

Lots of good information and advice in this thread. Only thing I will add is to shoot minimum 10 shots at 100 yards and zero your rifle based on that. Zeroing on a single 3 shot group has great potential to cause your rifles actual zero with that load to be off. And don't throw out "fliers"...those need to be included in the zero calculation as well.

 

[Wrench]

You don't NEED a chronograph....you need to be able to spot your hits at known ranges and backfill the info with your program. Do this at 1,3,4,5 and 6 and you WILL have a usable MV.

Pay attention to the pain in the butt part of what I posted earlier.....lrabs are not very fun to dial in.