Lets Talk Stepped BC's

[Broz]

BROZ,

Interesting ideas. How do you determine the correction for your second curve?.

Well that is why I started this thread. The only way I know is to shoot the actual distances at least every 100 yards and document drops. Then use this data to "Tune" BC and Velocity to match up.

Jeff

 

[Rocky Mountain]

Well that is why I started this thread. The only way I know is to shoot the actual distances at least every 100 yards and document drops. Then use this data to "Tune" BC and Velocity to match up.

Jeff[/QUOTET

The only down side I can see to that idea are very slight up and down winds to the target at extreme range, sometimes they are very hard to detect and can make you unsure of what is really happening with your true scope wind up.

 

[Broz]

Well that is why I started this thread. The only way I know is to shoot the actual distances at least every 100 yards and document drops. Then use this data to "Tune" BC and Velocity to match up.

Jeff[/QUOTET

The only down side I can see to that idea are very slight up and down winds to the target at extreme range, sometimes they are very hard to detect and can make you unsure of what is really happening with your true scope wind up.

Yes this is a fact. This is why you need to make the same shot over and over on different days while compiling data. I find early am best.

Jeff

 

[youngbuck]

Broz, you are in a position to use stepped BCs. You have a lot of data compiled, especially with the time in Idaho. I thought the 2 bullet option in shooter is pretty clever. You have the info to go back in and "tune" you BC to find a good fit. I'm pretty interested in the new program Bryan spoke of. The adjustable base sounds neat too. I need to stop reading your posts regarding rangefinders. The last thing my bank account needs is a PLRF.

 

[ken snyder]

I'm not an expert but I do shoot milk jugs at 1800yd. (only 1 out of 17 average ). There are only 2 BC's: supersonic and subsonic. All of the stepdowns are because the bullet does not match the standard profile worth a hill of beans. I feel that for ELR you need do figure out what your actual supersonic and subsonic BC is (out of your barrel). It doesn't matter what the bullet is rated at because they all swage up differentently in different barrels and at ELR small differences are tremendously large. Place a heavy metal plate in front of your second chronograph, find the distance that equals the last of supersonic velocity and then go out another 200yds. for subsonic. Now there is no more step up, down, sideways or inside-out BC popcorn balls. BC is a marketing substitute for shinola.

 

[Buffalobob]

For a couple of reason that I hope I have corrected, I am always low at ELR, usually about 1-2 MOA. I have reworked all of my charts and have both the G1 and G7 charts agreeing within 0.3 MOA at 2500 yards so we will see in a month and a few days whether that helps. I would say that between Bryan's book and his ballistic program, JBM and Exbal that things are looking much like the data that I was recording last year so hopefully I have my stars and ducks all lined up now. The thing is that at 2500 yards even 0.3 MOA is a big chunk of real estate.

 

[eddybo]

Maybe you can get Bryan to run you a you one of these. I could not get it to copy correctly but it is quoted from a thread here.

I ran a custom drag profile for the 7mm 200 grain ULD, see below:


Vel G1 BC G7 BC
4000 0.830 0.349
3900 0.819 0.351
3800 0.809 0.353
3700 0.799 0.355

I have resorted to stepped G1 BCs in a couple instances, it is a pain. About the only way I know to do it is get your actual drops and reverse engineer.
Other than that I am not saying anything in this thread.

 

[NZ Longranger]

Before the days of G7's, I used to run seriously stepped G1 BC's for my bullet of choice back then - the 7mm 180gn Berger VLD. These started at .710 out to 1000 yards and then progressively dropped until by 1700 yards I was using .4 G1. This shows how far from the G1 curve the VLD's actually are! Even with G7's I still had to step down beyond 1400 yards, but only a fraction of the G1 stepdown. So far with the Hybrids using G7, both 7mm 180's and the 338 Gen II 300's, we haven't had to step down at all out to 1400, and with the 300's to 1710 yards we also haven't needed to step down. We need to do more extended range testing with the 300's but so far to as far as we're prepared to shoot game in good conditions, the single G7 using "Shooter" is bang on. If you use G1 you'll have to use stepped BC's much beyond 1000 yards in my experience.
Greg

 

[Broz]

Before the days of G7's, I used to run seriously stepped G1 BC's for my bullet of choice back then - the 7mm 180gn Berger VLD. These started at .710 out to 1000 yards and then progressively dropped until by 1700 yards I was using .4 G1. This shows how far from the G1 curve the VLD's actually are! Even with G7's I still had to step down beyond 1400 yards, but only a fraction of the G1 stepdown. So far with the Hybrids using G7, both 7mm 180's and the 338 Gen II 300's, we haven't had to step down at all out to 1400, and with the 300's to 1710 yards we also haven't needed to step down. We need to do more extended range testing with the 300's but so far to as far as we're prepared to shoot game in good conditions, the single G7 using "Shooter" is bang on. If you use G1 you'll have to use stepped BC's much beyond 1000 yards in my experience.
Greg

Thanks Greg, I believe you are pushing the 300 Gen 2's quite a bit faser than I am. So that is probably the difference. But so far it looks as if I will need to step them at about 1400 yds. Time will tell as I still want another day shooting from 1400 to 2000 yrds to double confirm some drops with and with out look angles, and coriolis.

Jeff

 

[jmden]

Now those last two posts give some interesting info. I'm wondering if NZ hits the same fps at 1710 as Broz does at 1400 given environmentals. Using 2700fps for Broz and 3250 for NZ in Exbal (so vel. banded G1), with the same environmentals, finds about 1900fps for both at the above yardages.

 

[Broz]

Thats what I'm thinking jmden. I am running them right at 2800 @ 4200 feet.

Jeff

 

[NZ Longranger]

Jmden,
You've got it!
Greg