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What bc band for 338 300 berger.

 
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  #8  
Old 04-09-2013, 09:03 AM
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Join Date: Feb 2007
Location: Townsend, Montana.
Posts: 7,817
Re: What bc band for 338 300 berger.

My experiences past 1500 yards is to be spot on you need to use stepped BC's in some cases. Or as Yrcan says a custom drag curve. I have done quite a bit of work with the stepped BC's and velocity limits. The problem is I don't feel they are something that will work in all rifles with the same bullet. In my testing, BC'c for the same bullet will vary from rifle to rifle. It is my opinion that this is due to the different twist rates, number of lands, and how that barrel scribes the jacket as far as depth. Sharing stepped BC's is like sharing a precision load, it is custom to that rifle.

The best way I have found to work all this out is to shoot either paper or steel in flat terrain. Then document the actual group centers in relation to point of aim. Also keep on record all field conditions along with shot angle if there is one, coriolis drifts, latitude and azimuth. Then once the real data for each distance is recorded sit down, for an evening, and work with the program adjusting perimeters until all line up. I said earlier shooting steel or paper. Reason is I feel these things are very important for good data. You need to be able to put a tape on it to see the distance from point of aim. At these distances a dust cloud off a rock is great practice, but could leave room for a 1/2 moa error for data. Another thing I have learned is all the angles involved at these ELR distances can be very deceiving. The bullet coming in from a descending angle, the face of the target at an angle, all will set you up for a 2 moa correction and many times only 1/2 that is needed with the angles. This is why I like to document on paper or steel with a plumb target surface.

I am also seeing where at these distances past a mile the powder temp and MV variation is becoming more needed. Again only real data for one rifle will help us here. The variations in my rifles and loads are small, but they are a variation and need accounted for.

Any wind at these distances, and there almost always is, will also have an effect on elevation impact as well as windage. With a right hand twisted barrel a right wind will raise point of impact. A left wind will lower it. I believe this is a function of the bullet climbing into the wind or the opposite on a wind following the direction of the spin drift. My best data so far indicates about 1/4 moa per 1000 yards needs to be added for a right wind and taken away for a left wind.

As you can see, all this takes many hours just getting a rifle set up properly for ELR. The drifts will require many rounds down range to tame. But I am constantly working to improve and in just the laste few years my first round success rate has improved dramatically. 1st round impacts within 2 moa at 2000 yards plus are becoming a norm and I hope to real that in even more.

Jeff
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  #9  
Old 04-09-2013, 10:13 AM
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Join Date: Dec 2012
Posts: 429
Re: What bc band for 338 300 berger.

Thanks everyone that was a real big help.

Broz you pretty much laid it all out for me, I was wanting a stupid format and that answered every question pretty through for me. Thanks as well.
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  #10  
Old 04-10-2013, 12:31 AM
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Join Date: Dec 2012
Posts: 429
Re: What bc band for 338 300 berger.

I put some bc's in my droid shooter app and went shooting. The first cold bore was pretty close being I had no Idea where the bullets were going to go. I also had less than good day for shooting the winds were gusting and stopping, behind and left to right. I will get my wife to put the video up when she gets home I think either sunday or monday. After the dust settled I think I had 8-9 hits out of 12 on about a 30" rock. That included my cold bore and everything. I was shooting at 2137 yards. I shot once cold bore and was high then shot 2 more the same. So I took a full minute out and kept shooting. I was really happy with how things went. I feel the results were a great foundation to build off of. Thanks for that help everyone. I will get the video up for you guys.
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