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338 300gr BC

 
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  #8  
Old 10-03-2010, 08:16 PM
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Re: 338 300gr BC

Thanks for the input. I will look into the trajectory validation. The puzzling part is that with my f class rifle, the trajectories are usually within 0.25 moa out to 1000.
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  #9  
Old 10-03-2010, 09:30 PM
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Re: 338 300gr BC

I have a feeling that Kirby was running a custom BC for his AM as well. Might have been .81 in his gun ? Not sure. I use the .768 in exbal and 2832 MV in my edge. This is dead on for my gun .The chrono gives it 2870 at the muzzle and 2852 fifteen meters down range.

I wouldnt worry what the chrono says either..

DUH
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  #10  
Old 10-03-2010, 11:28 PM
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Re: 338 300gr BC

I actually use .820 for BC with my 338 AM and .800 for my 338 AX. Have always worked out fine for me.

The difference in trajectory at 1000 yards with 30 fps velocity spread is roughly 1/4 moa. Far less them most of us could tell with our shooting ability, putting me on the top of that list.

One thing you may have to play with is multipul BC values for various velocity ranges. THis can also help you tweak your drops.

Are your drops consistantly off over the entire trajectory or more one ended?
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Kirby Allen(50)

Allen Precision Shooting
Home of the Allen Magnum, Allen Xpress and Allen Tactical Wildcats and the Painkiller Muzzle brakes.

Farther, Faster and Flatter then ever before.

Web Page: www.apsrifles.com

allenmagnum@gmail.com
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  #11  
Old 10-03-2010, 11:44 PM
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Re: 338 300gr BC

Quote:
Originally Posted by canderson View Post
Thanks for the input. I will look into the trajectory validation. The puzzling part is that with my f class rifle, the trajectories are usually within 0.25 moa out to 1000.
With an ES of 30+ you will have a hard time matching a calculated long range trajectory.
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  #12  
Old 10-04-2010, 12:15 AM
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Re: 338 300gr BC

Trebark,

How do you figure that?

Check it with one velocity and see if it matches up, if not check the 30 fps faster velocity.

In most cases, 30 fps is not worth even worrying about, average the difference and use that velocity for your program.

30 fps spread will not make 1 moa of difference at long range(1000 yards) Not even close.

Here is an example of 30 fps variation at 1000 yards: My 338 AM with 300 gr SMK

3300 fps velocity and data at 1000 yards:
Retained velocity: 2303 fps
Retained energy: 3532 ft/lbs
bullet drop w/ 100 yard zero: 16.75 moa (174.2")
bullet drift w/ 10 mph crosswind: 3.0 moa (31.8")

3330 fps velocity and data at 1000 yards:
Retained velocity: 2327 fps (only 24 fps difference)
Retained energy: 3605 ft/lbs (73 ft/lbs difference)
bullet drop: 16.25 moa (1/2 moa difference)
bullet drift: 3.0 moa (no difference)

Now if you can consistantly hold less then 1/2 moa accuracy you MAY be able to see the difference of 30 fps at 1000 yards with this class of chambering but I know very few that can hold this level of accuracy consistantly shooting from field conditions.

A shooters ability to accurately judge shooting conditions will make MUCH more difference in the real world that 30 fps velocity spread.

Maybe I misunderstood your comments.
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Kirby Allen(50)

Allen Precision Shooting
Home of the Allen Magnum, Allen Xpress and Allen Tactical Wildcats and the Painkiller Muzzle brakes.

Farther, Faster and Flatter then ever before.

Web Page: www.apsrifles.com

allenmagnum@gmail.com
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  #13  
Old 10-04-2010, 09:04 PM
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Re: 338 300gr BC

What type of speed and group size are you getting.
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  #14  
Old 10-05-2010, 08:24 PM
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Location: Helena, AR
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Re: 338 300gr BC

Everyone thanks for helping. Kirby here is a little insight to what I have found. MV is 3200. The rifle is zeroed at 300. 600 drop come up is supposed to be 6.0 moa actual is 6.5 moa. 815yd 11.3 moa (this one was really close). 1000 yd come up 16.5 moa actual is 17.25 moa. 1200 yd come up is 22.8 moa actual was 24 moa. If yall can make sense of what is happening please help. Otherwise, I will back the target out 100yds at a time and see what happens. By the way Kirby, this rifle is a total balst to shoot. I was extremely fun listening to my 2' x 2' steel rings at 1200 today.
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