338 Lapua Drop Verification Question

[Hunter15]

To make a long story short, I worked up a load that my Savage 110 FCP HS Precision in 338 Lapua Mag likes. Shooting quarter MOA @ 100yds with 250GR Sierra MK's. Shot it through my Chrony and over a Magnetospeed. Chrony says avg fps were 2800. Magneto says 2840. I plugged the 2840 and all other data into my BulletFLT program very meticulously to ensure the accuracy of the data inputs. I headed to my range to verify the drop @ 820 yds. Program lists correction @ 20.0 MOA. after two misses and corrections I start to ring the plate. Those corrections brought me from 20 MOA to 18 MOA. I was not worried about wind deflection so I shot a group concentrating on the drop data. My group measured 2" vertically, which I was very happy with. Now here is the problem. To correct the program I have to bump my velocity from 2840 to 2945. That seems like a big jump to me. Especially since the velocity from the Magneto should be very accurate. Should I change the BC of the bullet also or should I leave it alone. The bc listed is .587 G1. is that the most recent data from sierra? Any suggestions would be greatly appreciated!

 

[dkhunt14]

Is your scope height correct? The distance from center of bore to center of scope. At long range this changes things. I like the G7 to find drops. I use Bergers Drops on their site and they have been very close. I even think the Sierra is on there. I thought the BC you used sounds low. I prefer to fudge the BC. The G1 BC on a Berger 300 is .818 and it runs close when I go to G7. Matt

 

[Hunter15]

My scope height is good. I've checked all my inputs over several time and everything is spot on. The main thing that bothers me is, I am pretty confident in the Magneto Speed Velocity. Changing it by over 100 fps to obtain my drop @ 820yds seems a bit much to me.

 

[bigngreen]

Did you verify turret click value?

 

[Hunter15]

Yep, verified that too. Are you guys in aggreeance with me that a 100 FPS velocity change seems a bit much to correct the program?

 

[Korhil78]

The G1 BC of the 250 SMK is .614. That would probably be your problem right there.

Using the BC that is correct (.614), I get 17.7 MOA up for 820 yards with my atmospheric conditions at hand right now and a velocity of 2840fps.

 

[Hunter15]

The G1 BC of the 250 SMK is .614. That would probably be your problem right there.

Using the BC that is correct (.614), I get 17.7 MOA up for 820 yards with my atmospheric conditions at hand right now and a velocity of 2840fps.

That could be some of the issue. I still get 19.5 MOA up for 820 using the same conditions as the evening I tested. Where did you get that BC from and what ballistic program are you using?

 

[Rimfire]

Is your range flat ground, any angle?

 

[Hunter15]

Is your range flat ground, any angle?

just a -3 degree decline

 

[lamiglas]

Hunter25,
To answer your one question, yes changing the velocity that much from confirmed magneto velocity is a lot to much. If i missed any of this i apologize ahead of time. What powder are you using? when you shot through the magneto, what was your ES? Good luck and I hope you get it all figured out. Maybe list all of your conditions and bullet data so we can run it in another program Apples to apples to eliminate program error possibility?

 

[bigngreen]

I would run a G7 of .314 which is probably same as the G1 as Korhil gave you but depending on the programs sometimes you will start to see the difference between the two in the velocity range your at with that range.
The Magneto tends to be very close, I don't feel comfortable moving from it more than 20 fps.
I think more data points would help so you get a feel for how the trajectory is, I'm at the point now where a Magneto speed velocity, solid data inputs and a Litz G7 and if I'm not within a small margin of error that I feel I can tune with a velocity I tune with the turret calibration, as long as I'm seeing a steady climb in the trajectory.

 

[Hunter15]

Hunter25,
To answer your one question, yes changing the velocity that much from confirmed magneto velocity is a lot to much. If i missed any of this i apologize ahead of time. What powder are you using? when you shot through the magneto, what was your ES? Good luck and I hope you get it all figured out. Maybe list all of your conditions and bullet data so we can run it in another program Apples to apples to eliminate program error possibility?

Good idea. To asnwer your first question my ES is 13 Fps. Below I will supply all program inputs.

Muzzle Velocity= 2840 Fps
Zero Rnage= 100 yds
Sight Height= 1.9"
Click Value= 0.25"
Bullet Mass= 250 GR (.338 Sierra MatchKing)
BC= .587 G1
Temp When Zeroed= 73 degrees
Pressure WHen Zeroed= 28.85
Angle When Zeroed= 0 degrees
Altitude When Zeroed= 0 (because local absolute pressure was used from Kestrel)

Inputs once at range...
Range= 818 yds
Temp= 61 degrees
Pressure= 28.72
Angle= -1 degrees
Wind Speed= 5mph
Wind Direction= 9 oclock
Altitude= 0 (because local absolute pressure was used from Kestrel)

Program outputs...
170.2" of drop = 19.9MOA= 79 clicks

to obtain an actual drop at 818 yds I had to adjust dial to 18.0 MOA

The gun shoots great from 100 yds all the way out to 818 but I cannot get the program outputs to match reality.

 

[Hunter15]

I would run a G7 of .314 which is probably same as the G1 as Korhil gave you but depending on the programs sometimes you will start to see the difference between the two in the velocity range your at with that range.
The Magneto tends to be very close, I don't feel comfortable moving from it more than 20 fps.
I think more data points would help so you get a feel for how the trajectory is, I'm at the point now where a Magneto speed velocity, solid data inputs and a Litz G7 and if I'm not within a small margin of error that I feel I can tune with a velocity I tune with the turret calibration, as long as I'm seeing a steady climb in the trajectory.

By turret calibration, do you mean adjusting the value of 1 click = .25" to a different value?

 

[Korhil78]

Can you list what it says when you put in a G1 BC of .614? Put all that data in there but change the G1 BC to .614. I am using the shooter app for my iPhone. That is the BC that Bryan Litz has for that bullet.