Need Help on How to Map Actual Trajectory with Software

[Full Curl]

Wondering if somebody with a lot more experience with ballistic programs can help me out here. I've been working up a load for my 7mm rem mag and am trying to verify drop charts that the software is telling me but I'm not able to match them up to what I'm seeing in the field very close. I'm currently using Strelok Pro software. Here's the info:

.284 caliber
160gr Nosler AB bullet G1 BC 0.531

Avg fps at 55-57 degrees 2,741 (StDev 23.21)
Avg fps at 57-59 degrees 2,767 (StDev 20.29)

100 yard (+1.69 inch vertical POI)
200 yard zero (+0.39 inch vertical POI)
287 yard (-6.18 inch vertical POI)
391 yard (-19.26 inch vertical POI)

I'm assuming that I need to "true" my velocity or the BC of my bullet to map this actual trajectory?? Not sure how to do that. Ultimately I just want some accurate drop charts. Any suggestions? Thanks.

 

[jpd676]

I have seen people make an error when they put in the scope height into the data inputs. Also, I shoot a 162 Amax in a 7mm mag, with a mild load of Retumbo and a 26" barrel I am getting 2950. Your speed seems a little slow. Also, sometimes chronographs aren't super accurate. When the battery on mine gets low I start getting weird speeds. Is your bullet impacting higher or lower than your data suggests?

 

[Full Curl]

I'm going to double check scope height tonight with calipers. As far as chrono, I'm not sure there. I don't have a ton of experience with them but these are the numbers from my Pro-Chrono and they are close to what I was getting last summer as well. I'm shooting 68.5gr of H1000 in a 26" barrel. The software tells me that I should have a higher impact at 100yds and lower at 391yds. What is "reasonable" deviation from actual POI to software POI at these ranges? I'm sure the data never matches 100%, but what should my goal be? I can report exact numbers tonight when I have the software tables in front of me. Thanks.

 

[MagnumManiac]

I'm going to double check scope height tonight with calipers. As far as chrono, I'm not sure there. I don't have a ton of experience with them but these are the numbers from my Pro-Chrono and they are close to what I was getting last summer as well. I'm shooting 68.5gr of H1000 in a 26" barrel. The software tells me that I should have a higher impact at 100yds and lower at 391yds. What is "reasonable" deviation from actual POI to software POI at these ranges? I'm sure the data never matches 100%, but what should my goal be? I can report exact numbers tonight when I have the software tables in front of me. Thanks.

This is what you should do.
Zero your rifle at exactly dead on at 200yrds, then shoot at 100, 300 and 400 to get your actual drops.
BC IS NOT A CONSTANT NUMBER. It changes with velocity and air density, therefore, no computer program will ever match your trajectory exactly. It will most likely be within a MoA or two, as long as all the info you input is correct.
I have even had an issue with one click up or down produced clean misses at over 1000yrds.

Try this, then tweak BC to match your actual drops in your ballistics program.

Cheers.
gun)

 

[jweigel]

The Strelok Pro has an option for Trajectory Validation option. It is the button with a blue up and down arrow and target. It should let you adjust your speed or BC. I usually adjust speed (if your twist is in the sweet spot for the bullet). The farther you shoot to validate....the better.

jjw
ND

 

[Full Curl]

I played with the "Trajectory Validation" function last night and was able to get real close to either 100, 200, 287, not 391 -OR- not 100, 200, 287, and 391. Maybe I'm splitting hairs here, but I just want to get it as close as I can so I can find accurate drops at 500 and 600yds. I also use a reticle with hold over points that I would like to be able to determine accurate POI numbers for that Strelok Pro can calculate as long as my trajectory data is accurate.

Like MM said, maybe I should shoot the test over again and see what results I get. I've shot it twice already and both times have gotten pretty close POI numbers. Tough for me to get very accurate POI numbers past 400yds with all the other shooting variables but as long as I can map 0-400 accurately, the software should get me real close out to 600 I would think with the drop charts.

 

[engineer40]

Tagging in. I'm interested in what people have to say about this.

Are you inputting your Barometric Pressure or your Station Pressure into Strelok?

 

[Full Curl]

Inputting barometric pressure but I usually take it from an online source for the area. I do not have an instrument to measure it.

 

[DUSTY NOGGIN]

I played with the "Trajectory Validation" function last night and was able to get real close to either 100, 200, 287, not 391 -OR- not 100, 200, 287, and 391. Maybe I'm splitting hairs here, but I just want to get it as close as I can so I can find accurate drops at 500 and 600yds. I also use a reticle with hold over points that I would like to be able to determine accurate POI numbers for that Strelok Pro can calculate as long as my trajectory data is accurate.

Like MM said, maybe I should shoot the test over again and see what results I get. I've shot it twice already and both times have gotten pretty close POI numbers. Tough for me to get very accurate POI numbers past 400yds with all the other shooting variables but as long as I can map 0-400 accurately, the software should get me real close out to 600 I would think with the drop charts.

what scope are you working with on this one

i would confirm your 200 is perfect then , shoot at the 600 then and record all of the variables for that day , try for a cooler no wind day ... get an average group POI on 10+ shots at the 600 , enter all those variables for the day you shot into your program , then adjust your speed in the to match

the better the details you put in the program the better the results you get out

 

[Full Curl]

I'm using a Leupold VX-3 4.5-14x 40mm with the Boone & Crocket reticle. Thanks for the suggestion. I didn't get a chance to shoot over the weekend but hope to soon. I re-checked scope height and confirmed it was accurate.

 

[DUSTY NOGGIN]

I'm using a Leupold VX-3 4.5-14x 40mm with the Boone & Crocket reticle. Thanks for the suggestion. I didn't get a chance to shoot over the weekend but hope to soon. I re-checked scope height and confirmed it was accurate.

thats not a bad scope at all , the old lady has the firedot sabr retical


[quote100 yard (+1.69 inch vertical POI)
200 yard zero (+0.39 inch vertical POI)
287 yard (-6.18 inch vertical POI)
391 yard (-19.26 inch vertical POI)][/quote]

it looks like you could go down one click to be closer to 200 zero .

https://www.leupold.com/wp-content/uploads/2016/02/Ballistic-Aiming-System-Manual.pdf

 

[Full Curl]

I'm going to see what the next range session brings for numbers and I'll post after that. Thanks for the information.

 

[LongBomber]

I like to shoot my drops out to at least 500 yards. I record all my information very carefully, atmospheric conditions, direction, elevation. I am very lucky t have places I can shot at the same target and keep stepping back. I end up with a target like the attached pic (6.5-284 with 140vld's, 100-500 yards in 100 yard steps) Very easy to work out when you can measure drops on one target.

 

[bigngreen]

You may have a couple things that are going to give you a challenge, nosler BC's are not correct so you need another source or work on it yourself, I looked and I could not find a Litz BC so you may be on your own which will mean some extra work for you.
Leupolds need to be ran through a tall target test to give you a solid understanding how it's moving, and run it at least 20 moa. You need to have this nailed down solid because it's critical because you'll need this to work in on an accurate BC and velocity.
Every number you can nail down hard will make it easier, a good range to target, correct scope height, an on site temp and station pressure is also huge.
I get all this stuff nailed down then when hitting the range I set a target at 100, 300, 600 and 1000 yards, you can't do this right with mirage, wind is fine but mirage will screw the whole program!! Depending on the rifle I will shoot all the targets or break it up, the idea is to get rounds on targets in the same condition then work the data, at this point I have a rifle grouping so I'm confident in putting one round on each target fast and working that data, two rounds on each if the rifle will permit it just backs up your data.
I shoot 100 and 300 for the reason of confirming zero, you will see a little variance of BC and velocity but if you see a large error from 100-300 you have basic numbers jacked up.
The 600 and 1000 yard target gives me an idea of how the trajectory changes so I can ID what number to tune. If you get this data set with attention to the quality of it and getting as much in on one condition as possible you can learn a lot and then sit down and work it.