Ballistic help for a newb?

[TheHack]

Hello,

Just getting started shooting longer range. After a miss on a hunting trip on a "chip shot" I'm going back to square one. I'm shooting a 138 grain Hammer Hunter at 3240 fps at 75F and 3140 at 27F. I got these velocities off a Bulletseeker Doppler. The Hammer estimated G7 BC is 0.198. 1:9 twist. Unfortunately, I don't have consistent access to a long range.

Last weekend I had access to a nice range. It was dead calm and 30F. I was making consistent hits on 12" plates to 600 yards. The 700 plate is small and I opted not to burn ammo. As the 800 plate is 16" and has a larger steel backstop I shot at the 12 o'clock edge of the plate (see photo). Sadly I could not see or hear my impacts at that range. I think the impacts at 800 have an elevation trend. The Kestrel and Revic ballistic apps call for a come up of 5.3-5.4 mils. I think I'm about 24" low at 800 yards which is 0.83 mils right? So 5.3+0.8=6.1. So of if I plug that into the Revic app under the "truing" portion I entered in 800 yards and 6.1 mils. The app throws an error (see photo) that says "inconsistent BC value, check input data". Can anyone give me some insight? Thanks for the consideration!

 

[ShtrRdy]

I don't know how the Revic app works but ballistic tables I've seen and used had a '0' correction at your sight in distance.

Something else curious is the warning message " Inconsistent BC value calculation ..."

 

[waspocrew]

Hello,

Just getting started shooting longer range. After a miss on a hunting trip on a "chip shot" I'm going back to square one. I'm shooting a 138 grain Hammer Hunter at 3240 fps at 75F and 3140 at 27F. I got these velocities off a Bulletseeker Doppler. The Hammer estimated G7 BC is 0.198. 1:9 twist. Unfortunately, I don't have consistent access to a long range.

Last weekend I had access to a nice range. It was dead calm and 30F. I was making consistent hits on 12" plates to 600 yards. The 700 plate is small and I opted not to burn ammo. As the 800 plate is 16" and has a larger steel backstop I shot at the 12 o'clock edge of the plate (see photo). Sadly I could not see or hear my impacts at that range. I think the impacts at 800 have an elevation trend. The Kestrel and Revic ballistic apps call for a come up of 5.3-5.4 mils. I think I'm about 24" low at 800 yards which is 0.83 mils right? So 5.3+0.8=6.1. So of if I plug that into the Revic app under the "truing" portion I entered in 800 yards and 6.1 mils. The app throws an error (see photo) that says "inconsistent BC value, check input data". Can anyone give me some insight? Thanks for the consideration!View attachment 629211View attachment 629212View attachment 629213

You need to put a value in for the POI offset. It can't be zero. Negative values since it's impacting low.

 

[waspocrew]

In the future, instead of guessing the additional correction, I would dial it and shoot to see what you actually need to impact at your POA. Then use that info in the app to true the profile.

 

[TheHack]

Thanks for the help! Would have dialed up instead of guessing but had limited range time. Also @waspocrew , I even watched the Gunwerks truing video and the guy in the video only enters his correction in MOA, does not enter a POI offset in inches. That said, I am trying your suggestion!

 

[Barbourcreek]

Is this correct

 

[BrentM]

Thanks for the help! Would have dialed up instead of guessing but had limited range time. Also @waspocrew , I even watched the Gunwerks truing video and the guy in the video only enters his correction in MOA, does not enter a POI offset in inches. That said, I am trying your suggestion!

The right way to do it is to use the reticle and view the difference in poa to poi and dial the scope up the correct amount. To a degree this removes those guesses in how many inches off you are etc and messing with the app.

It's odd to see such a low impact from 600 to 800. My suggestion is to check your scope tracking before doing anything more. Conduct a very simple tall target test and ensure you don't have an issue internally with the scope.

 

[TheHack]

Thanks for the suggestions.

Yes, it is odd that the drop from 600 to 800 is so dramatic, that is why I brought the issue here. I will check scope tracking, hope that is not an issue in this TT 3-15

As I noted, the 138 gr impact cannot be seen on a white steel background at 800 yards, otherwise I would just measure up with my FFP scope and do as suggested. Am driving to a range on New Year's Day and will collect more data.

Will report back with more info. Happy New Years!

 

[TheHack]

Is this correct

Windage aside, 6.1 MILS up is my napkin math.

 

[BrentM]

Thanks for the suggestions.

Yes, it is odd that the drop from 600 to 800 is so dramatic, that is why I brought the issue here. I will check scope tracking, hope that is not an issue in this TT 3-15

As I noted, the 138 gr impact cannot be seen on a white steel background at 800 yards, otherwise I would just measure up with my FFP scope and do as suggested. Am driving to a range on New Year's Day and will collect more data.

Will report back with more info. Happy New Years!

Missed that. Might barrow a spotting scope next time out. I am not in high humidity so impacts are usually easy to spot. Still a bit miffed on the impacts being that low. I think what I'd do is double down on the data and make sure it's extact. Do another range session and see if it's repeatable, take a spotting scope to ensure all impacts at all ranges are center and confirm. If you impacts at 600 we're not center, but actually a little low, then I'd definitely think your data is off.

 

[TheHack]

Missed that. Might barrow a spotting scope next time out. I am not in high humidity so impacts are usually easy to spot. Still a bit miffed on the impacts being that low. I think what I'd do is double down on the data and make sure it's extact. Do another range session and see if it's repeatable, take a spotting scope to ensure all impacts at all ranges are center and confirm. If you impacts at 600 we're not center, but actually a little low, then I'd definitely think your data is off.

Thanks Brent, will do! I will post my new data after the New Year.

 

[BrentM]

Thanks Brent, will do! I will post my new data after the New Year.

You can pm the data if you want someone to look it over and double check. I am thinking your chrono data needs to be double checked too. I understand your desire to do mv adjustments but unless you can dial the scope to center impact or measure the drop (not guess) it is a little bit of a swag that can cause more headaches.

 

[Sdvldog1371]

You can get your zero offset for your calculator at closer range. If you settle in behind your rifle and build a really good position and then shoot 3 shots at 100, then make any corrections to get it as close to zero as possible. After it is as close to perfect as possible, you measure how far the center of the group (at 100 it should be a bughole) is from the center of the target. It may be less than 1/4" but that offset grows at distance.

Also, your Calculator wants an azimuth and angle because it plays into the calculations. So does wind direction to an extent. Literally having a zero shot on a north south isn't fully accurate east west, you can change that variable in your app and look at the data at 600+ yards. It will change slightly.

Having a trued zero offset and your angle and direction helps the calculations and software to evaluate the true BC. Having your velocity trued is a matter of shooting a group beyond 400 with the given data and then measuring how far off that data was and entering that offset.

 

[med358-boise]

You didn't mention what your zero range is - should we assume 100 yards?