Flatter than calculated trajectory

[boltfluter]

Make sure your zero at 100 yds is dead on, as this slight error will be greatly exaggerated at distance. This has bitten me more than once over the years. I am sure you are doing this, but be sure and get your zero at the same range, location wise, that you are doing the test at. Good luck and let us know how it goes.
Paul

 

[Jeff Porter]

I would set the JBM to zero at your target distances and look at the inches up at 100 yards for those. So for your example 8.1” up at 100 for 600 yard zero.

Set rifle to 100 yard zero and shoot a centered group at 100. Add the 6.25 dial up and check impact on your 100 yard target.
If tracking right it should be up 6.25 but if it is higher than that, you have a contributing factor. Continue adding I’d needed to get to the 8.1” up. See if that explains any variation in point of impact versus dialed setting. I know you did a tracking test but I am presuming that was just running the knobs and looking at a grid target and not firing a round. Recoil can matter.

Scope tracking and BC adjustment and true MV are likely all combining to give the results you are seeing.

 

[std7mag]

Hi 357Mag,

I did input the measured distance between bore centreline and optic centreline. It was almost exactly 2.0".
Thanks

This is at the objective of the scope, not the center of the scope, correct?

 

[dellet]

Something that is very easy

I would set the JBM to zero at your target distances and look at the inches up at 100 yards for those. So for your example 8.1” up at 100 for 600 yard zero.

Set rifle to 100 yard zero and shoot a centered group at 100. Add the 6.25 dial up and check impact on your 100 yard target.
If tracking right it should be up 6.25 but if it is higher than that, you have a contributing factor. Continue adding I’d needed to get to the 8.1” up. See if that explains any variation in point of impact versus dialed setting. I know you did a tracking test but I am presuming that was just running the knobs and looking at a grid target and not firing a round. Recoil can matter.

Scope tracking and BC adjustment and true MV are likely all combining to give the results you are seeing.

what I would add to this is that is very simple to zero at 600, return to 100 and measure point of aim, point of impact difference.

Zero 100, zero 600, return to 100 check impact over aim.

Same check over multiple distances doesn’t hurt.

 

[Eagle Six]

The Applied Ballistics calls for 5.75 MOA up.

Edit: This is incorrect.

 

[SKWERLZ]

The Applied Ballistics calls for 5.75 MOA up.

I get a a similar result with ballistic AE and I guessed a DA of about 1600 with op’s stated temp and altitude.

 

[Brians356]

Make sure your zero at 100 yds is dead on, as this slight error will be greatly exaggerated at distance. This has bitten me more than once over the years. I am sure you are doing this, but be sure and get your zero at the same range, location wise, that you are doing the test at. Good luck and let us know how it goes.
Paul

Personally, I don't think much about horizontal when shooting groups. I concentrate on holding consistent vertical even in breezy conditions. I'm interested in minimal vertical spread.
-

 

[17Hornet]

Make sure your zero at 100 yds is dead on, as this slight error will be greatly exaggerated at distance. This has bitten me more than once over the years. I am sure you are doing this, but be sure and get your zero at the same range, location wise, that you are doing the test at. Good luck and let us know how it goes.
Paul

I'll double check it before the field test. Thanks

 

[17Hornet]

I would set the JBM to zero at your target distances and look at the inches up at 100 yards for those. So for your example 8.1” up at 100 for 600 yard zero.

Set rifle to 100 yard zero and shoot a centered group at 100. Add the 6.25 dial up and check impact on your 100 yard target.
If tracking right it should be up 6.25 but if it is higher than that, you have a contributing factor. Continue adding I’d needed to get to the 8.1” up. See if that explains any variation in point of impact versus dialed setting. I know you did a tracking test but I am presuming that was just running the knobs and looking at a grid target and not firing a round. Recoil can matter.

Scope tracking and BC adjustment and true MV are likely all combining to give the results you are seeing.

We fired 3rd "groups" to validate tracking (running low on ammo at that point). Tracking was within 1/4MOA of dialed. So dialed up 10, got 10.7" travel, instead of the 10.47" we asked for. I'll have him do the test at multiple ranges with a constant zero to see what we are getting.

 

[17Hornet]

This is at the objective of the scope, not the center of the scope, correct?

Correct. Measured at the objective lens, to bore centreline.

 

[17Hornet]

Something that is very easy

what I would add to this is that is very simple to zero at 600, return to 100 and measure point of aim, point of impact difference.

Zero 100, zero 600, return to 100 check impact over aim.

Same check over multiple distances doesn’t hurt.

Makes sense. I'll probably end up doing something like this next time I'm out with him. If nothing else, it gives additional data to make a corrected chart.

 

[dcali]

Generally with stuff like this, step through every potential source of error, starting with the biggest ones - velocity, range, bc being the usual culprits. And double check you're not doing something stupid like dialing from the wrong baseline.

My guess would be you selected G1 instead of G7, but look through all of it. You'll find something.

 

[17Hornet]

The Applied Ballistics calls for 5.75 MOA up.

Would you be willing to post a screenshot of your entered data? I'm thinking perhaps I have entered something wrong.

I tried using the Applied Ballistics online calculator to check, but when I hit enter the screen just goes white and it doesn't process any results.

 

[17Hornet]

I get a a similar result with ballistic AE and I guessed a DA of about 1600 with op’s stated temp and altitude.

Would you be able to post a screenshot of your entered data? At this point, I'm thinking I may have entered something wrong.

 

[17Hornet]

Generally with stuff like this, step through every potential source of error, starting with the biggest ones - velocity, range, bc being the usual culprits. And double check you're not doing something stupid like dialing from the wrong baseline.

My guess would be you selected G1 instead of G7, but look through all of it. You'll find something.

Everything has been checked that I can think of. I have the correct G7 BC entered, range was checked with 2 rangefinders, velocity data was gathered on 2 separate days. The average for the first day was 3317fps and the average for the second day was 3340fps. The second day was about 6⁰C (~11⁰F) warmer than the first day.

I will double check his dialing next time we are out - I was letting him take care of all of that last time.

 

[Brians356]

Targets:
-100 yard target is located SSW of bench
-600 yard target is almost due West of the bench

This suddenly jumps out at me. You're having to shift your setup to change direction between the two distances, approaching 90 degrees. Also the light is changing, especially in sunlight when there may be mirage. For digging into trajectories at two distances, all else needs to be the same as much as possible. Can't you shoot the 100s in the same direction as the 600? Or, can you shoot 100 and, say, 200/300 in the same direction just for this investigation? All I'd be comfortable with is necessary slight elevation angle changes without relocating bags. Or are you using a turntable bench (ugh!)?
-

 

[Eagle Six]

Seems there is considerable difference between JBM and my AB and @SKWERLZ Ballistic AE calculators.

I made some assumptions as entered data that you have not provided, so correct me if I am wrong

Barrel twist 1:7.5, right
Sight Height 2.0 inches
Sight Offset 0 inches
Bullet Diameter .224
Bullet Weight 75 grains
Bullet Length 10119 inches
Muzzle Velocity 3340 fps
Powder Temperature 43 F
G7 .266/.235
Altitude 2788 ft
Corrected Pressure 30.17
Temperature 42.8 f
Humidity 60%
Wind Speed 6.2 mph
Wind Angle 135 degrees
Latitude 60 N
Azimuth (when shooting 600 yards) 270 degrees

 

[dcali]

Everything has been checked that I can think of. I have the correct G7 BC entered, range was checked with 2 rangefinders, velocity data was gathered on 2 separate days. The average for the first day was 3317fps and the average for the second day was 3340fps. The second day was about 6⁰C (~11⁰F) warmer than the first day.

I will double check his dialing next time we are out - I was letting him take care of all of that last time.

Something is definitely wrong. Double check everything again. Somewhere you're not doing what you think you're doing.

 

[17Hornet]

This suddenly jumps out at me. You're having to shift your setup to change direction between the two distances, approaching 90 degrees. Also the light is changing, especially in sunlight when there may be mirage. For digging into trajectories at two distances, all else needs to be the same as much as possible. Can't you shoot the 100s in the same direction as the 600? Or, can you shoot 100 and, say, 200/300 in the same direction just for this investigation? All I'd be comfortable with is necessary slight elevation angle changes without relocating bags. Or are you using a turntable bench (ugh!)?
-

The reason we are setup this way is due to the topography of the coulee - this is the way the backstops have naturally arranged themselves. We will be moving to a field next time we shoot and everything will be in the same direction (should be NW if memory serves). Ideally I'd take him out to my range, but that's a 2+ hour drive for him. Maybe I'll convince him eventually. Lol

 

[17Hornet]

Seems there is considerable difference between JBM and my AB and @SKWERLZ Ballistic AE calculators.

I made some assumptions as entered data that you have not provided, so correct me if I am wrong

Barrel twist 1:7.5, right
Sight Height 2.0 inches
Sight Offset 0 inches
Bullet Diameter .224
Bullet Weight 75 grains
Bullet Length 10119 inches
Muzzle Velocity 3340 fps
Powder Temperature 43 F
G7 .266/.235
Altitude 2788 ft
Corrected Pressure 30.17
Temperature 42.8 f
Humidity 60%
Wind Speed 6.2 mph
Wind Angle 135 degrees
Latitude 60 N
Azimuth (when shooting 600 yards) 270 degrees

Yeah, that all looks correct. I just checked JBM again and it matches the data I have entered there as far as I can see. Maybe I just have to fork over for the Applied Ballistics app...

Thanks for posting your inputs!