Adjusting input data for ballistic programs

[trophyhusband]

I need a little help here. I just got a G7 BR2 rangefinder but It doesn't give me the right correction for my 6.5 Grendel. It does, however give me the right correction for my 300WM. For my Grendel, Strelock always puts me about 4 MOA low at 1000 yards and the G7 BR2 puts me even lower. All ballistic programs I've looked at give low to varying degrees so I'm convinced that this is a bad input=bad output situation. My question is this, should I adjust the muzzle velocity down or the BC down, or something else I'm not thinking of to get it to come out right? I don't just shoot this at 1000 yards, but occasionally out to 1200 yards and sometimes I like to move in to 500 yards. I also want to hunt deer with it so whatever input numbers I fudge will have to give me an accurate output across all ranges.

 

[Bart B]

Have you chronographed your loads in field conditions then input the average muzzle velocity into the G7 BR2?

 

[trophyhusband]

I've chronoed and averaged on one day but not averaged over several different days of varying weather conditions. Temp sensitivity factor is also suspect.

 

[Bart B]

What altitude did you get a zero at? If it's a couple thousand feet different than you hunt in, that'll cause a 2 MOA vertical sight setting.

 

[BMF]

1)I was under the impression that the G7 automatically adjusted for elevation by calculating the air pressure?
2) What are the numbers you are inputting?

That's a fairly popular round. Someone may have a similar load and could cross reference it with their G7
_____________
Brent

 

[jackem]

I need a little help here. I just got a G7 BR2 rangefinder but It doesn't give me the right correction for my 6.5 Grendel. It does, however give me the right correction for my 300WM. For my Grendel, Strelock always puts me about 4 MOA low at 1000 yards and the G7 BR2 puts me even lower. All ballistic programs I've looked at give low to varying degrees so I'm convinced that this is a bad input=bad output situation. My question is this, should I adjust the muzzle velocity down or the BC down, or something else I'm not thinking of to get it to come out right? I don't just shoot this at 1000 yards, but occasionally out to 1200 yards and sometimes I like to move in to 500 yards. I also want to hunt deer with it so whatever input numbers I fudge will have to give me an accurate output across all ranges.

Over at the Grendel forum there is a thread about the actual BC of the AMAX pill being different than advertised.

http://www.65grendel.com/forum/showthread.php?10705-123-amax-BC

Jack

 

[C.O. Shooter]

Have you done any trajectory validation? I would shoot at 400, 600, 800, and 1000 yards. Figure out your drops. Use your current muzzle velocity to start and adjust according to your drops.

This is a good tutorial.

[ame]http://www.youtube.com/watch?v=dWpTVbXlspk[/ame]

 

[trophyhusband]

I just got back from shooting at 500 yards. It was quite a bit warmer than conditions i normally shoot in. Strelock and the G7 agreed on the correction (500 yards was ranged with a Bushnell 1200) and my shot was almost 2 MOA high.

 

[trophyhusband]

What altitude did you get a zero at? If it's a couple thousand feet different than you hunt in, that'll cause a 2 MOA vertical sight setting.

My zero and testing have all been done at 5100 feet. I haven't hunted deer with the Grendel yet (and unfortunately won't be using it this year). I do enter elevation. Into Strelok and the G7 has a barometer so it makes the correction for altitude. I shot my elk at 8000 feet with my 300WM using the correction given by the G7. I didn't run the numbers through Strelok for that shot.

 

[trophyhusband]

1)I was under the impression that the G7 automatically adjusted for elevation by calculating the air pressure?
2) What are the numbers you are inputting?

That's a fairly popular round. Someone may have a similar load and could cross reference it with their G7
_____________
Brent

Yes, the G7 corrects for elevation. Input muzzle velocity is 2580 and BC is .510 in both Strelok and the G7. The G7 determines air pressure and temp. I enter weather data in strelok given by a Sky master. Strelok also asks for temp sensitivity factor which is set at 1.4.

 

[trophyhusband]

Have you done any trajectory validation? I would shoot at 400, 600, 800, and 1000 yards. Figure out your drops. Use your current muzzle velocity to start and adjust according to your drops.

This is a good tutorial.

http://www.youtube.com/watch?v=dWpTVbXlspk

I havent, but I'll watch the tutorial and give that a try after deer season.