338 Lapua Drop Verification Question

[lamiglas]

I should have time this evening to rum it through my bullet flight. One more question. Did you use the same method for zeroing as when you shot for validation? (Prone, bipod, rear bag etc.)?

 

[Hunter15]

korhil, when I replcae the .587 BC with your suggested .614 BC the output is 19.5 MOA. Still doesnt get me close to the 18.0 I dialed.

lamiglas, that is the only thing I wasn't consistant with. I zeroed the rifle sitting on my bench with bipod and rear bag. I shot 818 yds prone, with the same bipod and rear bag.

 

[Korhil78]

Yea...I put in .641 and it gives me 17.4(820 yds). 17.7 is for 830 yds when I put in the atmospheric conditions from my kestrel. .587 to .641 won't really change your drop that much at 820 yds so hopefully you figure out what is wrong. I have never used bullet flight so I am no help there.

 

[RockyMtnMT]

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.

You say that your click value is .25", then you are dialing moa. Try setting your ballistics program for IPHY instead of moa. Then you should be on the money.

Steve

 

[Wachsmann]

I have experienced a similar issue. when shooting at 750 yards. I used someones mag speed chrono at the range but only for 3 shots same powder charge that I always use and it reported 2973-2967-2960 for a 3 shot group. I shot at the 750 yrd mark to validate and I was about 3 to 4 inches high. I used the G7 program and it shows I was running at 3016fps to match the drops. So from what I'm hearing is that usually the mag speeds are always accurate say within 20 fps. I dialed originally for 13.5 but kept shooting high. I dropped .5 moa on my scope and hit the jug center right. The I shot several more shots at the 13moa for group. Gun and shooter shoots about .6moa at this distance. But like everyone has pointed out it could be a number of things. My scope is .5 MOA click value so I'm going to always have a little low or high fudge factor. load is a 230 berger, 89.3grn retumbo, 300 ultra mag. one thing that may been the biggest game changer was I had to open a new 1 lb of retumbo so this lot might be slightly different. forgot about that till now.