Ballistics Trueing

[zer0dev]

I'm pretty stumped here...

I'm shooting my first NRL22 match this weekend, so I went to the range this week to true the gun in Strelok. I've been using the app for a while so I'm familiar with it, however this is the first time I've had access to a real range and the first opportunity to test what it's saying out to any good distance.

The gun is a .22 Impact M3 with the heavy liner, shooting 34gr Javelin / H&N Heavy slugs at ~990 fps. I verified the velocity with two different chronographs (FX wireless and a ProChrono). Strelok is setup with all the correct info on the gun and ammo (0.118 BC @ G1), re-checked the scope height and everything (though this has little impact down range).

I zeroed the gun at 50 yds. Trust but verify... checked the targets with my range finder and good at 50 and 100. According to the app, it's 6.9 MOA from there to 100 yds. Well, it's not. It's 5.5. I went back to check my 50 yd zero and it hadn't moved. I had the chrono at the range and velocities didn't change. Tried both slugs, both sitting at 5.5 MOA at 100 yds.

The Strelok trueing feature wasn't even able to calculate a BC adjustment. The velocity adjustment was 1092 fps!! Like I said, verified 990 with two different chronos. But the new adjustments don't lie. I picked a target at 70 yds after the adjustment, 1.6 MOA, and it was dead on. So I'm confident this will work for the match... but I just don't get it. I also don't know if it will hold out to 150/200. I have access to a 200 yd range and might play around after the match.

I played around with other drag functions in Strelok and nothing really made a difference of more than 1/2 MOA at 100. I picked some random bullet in the list and it did get me to 5.8 MOA, but that's not reliable.

Thoughts? Anyone experienced the same?

 

[Franklink]

I was playing with a .22 slugger yesterday, also shooting the 34grains (varmint knockers in my case) and noticed how flat it is with a 0.12 BC plugged in. And actual was matching pretty closely to Strelok-predicted.

You'll notice the "zero" is really something like 29-53 yards with this setup. Perhaps try changing the "zero" distance within Strelok to be somewhere between that 29 and 53 yards and see if that straightens it out for the 100 yard shots.

 

[Franklink]

Things like a tailwind/headwind and humidity levels can also change actual and ballistic app-predicted.

 

[zer0dev]

Thanks. I should have mentioned I updated weather in Strelok, and there was no significant wind. Even with a tail wind... 1.5 MOA seems outrageous at 100 yds. We're not talking 250/300. Margin of error at 100 can't be that large.

I'll see what changing the zero distance might do. But I set it to 50 and I zeroed at 50. Doesn't seem like that's something that should be "played with" to get the right dope.

 

[oOmpH]

Check your scope height data. Most likely culprit.

 

[zer0dev]

Check your scope height data. Most likely culprit.

Yep did that. Spot on. Incidentally, scope height is 3.19 in. If I change it to 4 in as a test, 100 yd adjustment comes down only to 6.1.

 

[Franklink]

....Doesn't seem like that's something that should be "played with" to get the right dope.

Unfortunately, tweaking the settings to get actual to match predicted has been necessary with all of the Strelok profiles that I've made. And that's from 20fpe all the way up to 100fpe.

And in some cases, it won't ever match perfectly.

 

[zer0dev]

I wonder how close dope is between a profile tweaked by zero distance, and one by velocity. I'll bet pretty close until further distances where the velocity change will affect drop more than the zero distance.

Testing at 200 yds will probably bear that out.

 

[Franklink]

I wonder how close dope is between a profile tweaked by zero distance, and one by velocity. I'll bet pretty close until further distances where the velocity change will affect drop more than the zero distance.

I agree.

The BC value plugged into Strelok becomes pretty important once it gets out there a ways too. You might even see if something like 0.13 as a bc value matches actual better.

BCs provided by slug companies are also only suggestions. Similar to how Strelok suggestions are only predictions, the BC your barrel/slug/conditions combination is producing may not be exactly what the slug manufacturer is advertising.

 

[zer0dev]

So I played with zero distance real quick. I need essentially a 25 yd zero to get 5.5 at 100. And I know that's wrong for 25yds. It's also wrong for 70 yds.

The truth probably lies in between. I need more data at distance past 100 to dial it in. Next week if I'm lucky.

But this weekend's NRL22 match only goes out to 100 so I should be golden with the current profile.

 

[Ries]

There is a "trueing" feature aka trajectory validation in Strelok. There you can enter how much drop you had at 100 yards and it will recalculate the BC

 

[zer0dev]

There is a "trueing" feature aka trajectory validation in Strelok. There you can enter how much drop you had at 100 yards and it will recalculate the BC

Yes, that's exactly what I did. The BC would be so outrageous that Strelok refused to calculate it lol. You can true by BC or velocity, which is why I went with velocity.

 

[OldSpook]

Yes, that's exactly what I did. The BC would be so outrageous that Strelok refused to calculate it lol. You can true by BC or velocity, which is why I went with velocity.

What constitutes "outrageous"?

 

[OldSpook]

Regarding adjustments to any ballistics program when truing the model to the world.

(1) Measured data is ALWAYS more "true" than computed data unless there is something very wrong with the sensor. So STICK to that number when you have measured it.

(2) BC is usually measured at one (or a very narrow) range of velocities, you go above or below that and you can easily see a 100% change, usually less but 25% is nothing.

(3) Remember your program is a model and the real world is something you can observe. Make the model match the world. If you can verify that it matches the world it doesn't matter if it makes sense.

 

[Scotchmo]

What scope are you using? And what are your scope settings in Strelok?

Also, if muzzle velocity is much above 900fps, RA4 (instead if G1) can get you a little closer.

 

[zer0dev]

Regarding adjustments to any ballistics program when truing the model to the world.

(1) Measured data is ALWAYS more "true" than computed data unless there is something very wrong with the sensor. So STICK to that number when you have measured it.

(2) BC is usually measured at one (or a very narrow) range of velocities, you go above or below that and you can easily see a 100% change, usually less but 25% is nothing.

(3) Remember your program is a model and the real world is something you can observe. Make the model match the world. If you can verify that it matches the world it doesn't matter if it makes sense.

That's good advice, thank you. Unfortunately I don't have something like a labradar to do a BC calculation, and I don't know if the range would allow me to put a chrono in front of the target (it's an idea though). Might be ok at my own risk.

What scope are you using? And what are your scope settings in Strelok?

Also, if muzzle velocity is much above 900fps, RA4 (instead if G1) can get you a little closer.

Element Titan 5-25x56, 3.19in scope height (using the AirMarksman backbone). Strelok has the scope in its database.

I experimented with the other drag functions. At that speed and distance RA4 (even with the different RA4 BC of the Javelins) didn't make much difference.

 

[OldSpook]

Is it an FFP?
It is a trivial matter to increase or decrease BC until you zero in on a correct/working value.
So, you have a means to measure drop relative to a certain zero. You already know muzzle velocity and all the other parameters. If all of that is good, and you are not using an SFP which is not set to the reference magnification, all you have to do is increase or decrease the BC until the drop figures match what you are measuring on the targets. It really doesn't even matter what drag model you use once those numbers match ( at three points a) between you and your zero, b) at your zero, and c) at some point down range, the farther the better) you are golden. No labradar needed.

 

[zer0dev]

It is an FFP. But I think to get the correct BC (or multi BC) I need the V1 velocity at the target to coordinate with the drop value. I don't have that without a labradar or a chrono down range.

I tried adjusting the BC to get the correct drop of 5.5 MOA and it didn't make sense. A BC of 1 gets me a drop value of 5.7 MOA which... honestly... is pretty close to real world. The 70 yd adjustment looks right. But that BC just can't be right can it? I need to stretch this out to 200 and see what those numbers look like.

This reminds me of that video Ted did a while back where his calculations were not matching up to real world drop.

 

[OldSpook]

It is an FFP. But I think to get the correct BC (or multi BC) I need the V1 velocity at the target to coordinate with the drop value. I don't have that without a labradar or a chrono down range.

I tried adjusting the BC to get the correct drop of 5.5 MOA and it didn't make sense. A BC of 1 gets me a drop value of 5.7 MOA which... honestly... is pretty close to real world. The 70 yd adjustment looks right. But that BC just can't be right can it? I need to stretch this out to 200 and see what those numbers look like.

Drop observed is hard to measure and you should do it by shooting three or four five shot groups and then averaging the observed drop. You have to do that at each test range to get meaningful data. This presumes you are shooting on level ground and all other conditions are correctly entered. I'd use G1 in the case of slugs and GA in the case of pellets but even that isn't going to make a big (as in easily measurable) difference. Remember measurement errors have to be taken out of the equation by taking a number of measurements and averaging them. Also if you can't measure it, you probably don't care because you aren't that accurate at that range. You have to be holding a pretty small group to be measuring a half MOA of difference in drop.

Again if your prediction matches your observation you have achieved your goal. Sure stretching it out is going to give you more data points and perhaps help you with setting up a multi-BC but get the close stuff done the best you can and then go try the long shots. It's a process.

 

[Scotchmo]

“At that speed and distance RA4 (even with the different RA4 BC of the Javelins) didn't make much difference.”

Not “much” but it will make some difference. It gets you closer to what you want.

Also, the Javelin BC estimates are given for 950fps. If you measured the BC at 990, it would likely be considerably higher for G1 and maybe a little higher for RA4. I’d use an RA4 BC of 0.12 to start. A single BC might be OK with RA4. If using G1, likely need to use multi BC to get your trajectory to align better at all farther distances.

Verify your zero. It’s easy to be off by a couple clicks.

Next:

Verify your distance using a tape measure. Easy to be off by a yard or two.

Next:

Verify your reticle spacing. Draw two lines on your exactly 100yd target at 10” apart. The reticle should read them at about 9.5 MOA spacing.

Also remember that distance for drop is measured from muzzle to target. Distance from reticle to target is a little more. That can change it another click.