Tweaking bc’s

Chase723

Well-Known Member
Joined
Nov 22, 2009
Messages
531
Couple things. This is all based on the assumption that your scope tracks perfect in addition to what has already been mentioned.

First, for velocity, the number you get from a chronograph is not absolute. Like has been mentioned, it’s a starting point. Even a Magnetospeed being 99.5-99.9% accurate is going to give you a variance of 3-15fps in a 3000fps rifle. So it gets you really close but you need to true it based on your come ups before BC has a major effect. 500 yards is a great place to do this. 15fps doesn’t seem like much but combine this with what I mentioned above and it easily accounts for your difference. Are you centered punching steel at 500? Or are you off .1-.2 mils? Don’t discount that. The bullet never lies.

Second, there is always going to be some BC variation from barrel to barrel so once you true your velocity you need to true your BC at distance. Since you can shoot at 800, once you know all of the above is correct and you have tried your velocity, adjust your BC at 800 to match your come up. Then shoot at 300, 400, etc on out to make sure it all lines up.

Hint, if after adjusting your BC you now notice that your on target DOPE for targets at closer distances doesn’t match up to the adjustments as indicated by your ballistics calculator then either your zero offset, scope height, velocity, or scope tracking, or a combination thereof, are not correct.
 

azsugarbear

Well-Known Member
Joined
Sep 20, 2005
Messages
1,466
Location
Central AZ
To answer your question, I have had to modify my BC's anywhere from 0.2 to 0.4. But this was back in the old days when we were still using the G1 BC instead of the more accurate G7 BC used for VLD bullets. However, this modification was done only after verifying items mentioned above: (1) scope is tracking true MOA (measure at least 20 moa up on a target using a plumb line); (2) making sure your zero is exact and not hitting 1/8" high or low (if it is, then you need to compensate for that in your data input). These are the two biggest culprits, but there are more as mentioned above. When you tweak the BC, you will most likely find that the new solution will have you hitting a little high in the 400-600 yds range (assuming 200 yd zero) and a little low beginning around 1000 yds. Although it may be a little off, it will not make any difference as you will still be well within the kill zone of you animal.
 

david g ranes

Well-Known Member
Joined
Sep 9, 2009
Messages
580
To answer your question, I have had to modify my BC's anywhere from 0.2 to 0.4. But this was back in the old days when we were still using the G1 BC instead of the more accurate G7 BC used for VLD bullets. However, this modification was done only after verifying items mentioned above: (1) scope is tracking true MOA (measure at least 20 moa up on a target using a plumb line); (2) making sure your zero is exact and not hitting 1/8" high or low (if it is, then you need to compensate for that in your data input). These are the two biggest culprits, but there are more as mentioned above. When you tweak the BC, you will most likely find that the new solution will have you hitting a little high in the 400-600 yds range (assuming 200 yd zero) and a little low beginning around 1000 yds. Although it may be a little off, it will not make any difference as you will still be well within the kill zone of you animal.
To get my clicks to match my ballistic app I had to go from .268 to .288 for the bc on my 22 creedmoor shooting 85.5 Bergers my 6 mm shooting 105 vld hunting it went from 278 to 298 to get the app to match my impacts it stayed pretty consistent at 400 but I realize things don’t start changing much till around 600 on the 22 I have a huskemaw with third moa clicks do I realize that’s not as precise if movements but I like the cross hairs on them better than any thing else. David
 

TBell

Well-Known Member
Joined
May 12, 2012
Messages
164
Location
Texas
I use Ballistic AE in my iPhone and I point my bullets or trim, so the BC had to be calculated using drop and velocity.
The app is not always spot on, but close.
I have also found that my BC out of my 338-416 Rigby Improved has higher BC with all bullets due to it’s higher velocity.
It’s not huge, but is different.
Without altering bullet profiles, Ballistic AE is very good and accurate with the listed bullets in the app archive. The BC’s are based on Litz’s data.

Cheers.
Yep have had good luck wit AE Ballistics, even using magno....clamp on chronograph. Sigh-in (without) at 100, then check speed, put in to AE app. go to 600 yards, shoot at 24” steel. Has always been on steel, then adjust the 4”-8” (+-) in the reconciliation part of the app. It corrects the velocity, save to that projectile in software, and i’m good. i am not a target competitor, but it has proven to be on the mark for me. Then confirm on 400 target from same location.
 

Flintlock shooter

Well-Known Member
Joined
May 2, 2018
Messages
98
Location
Spokane WA
Accurate MV will give you a accurate rifle out to about 650 yards. Beyond that it requires a accurate BC. BC is best developed within 10% of the range at which your bullet goes transonic. When truing the BC if you are hitting high, raise the BC. If hitting low, lower the BC.
BC has to be developed for each barrel. Some may have the same BC, but not all.
 

BrentM

Well-Known Member
Joined
Jan 10, 2013
Messages
3,094
Location
Meridian, Idaho
I have a mag and lab for velocity checking. Both excellent. Out to 1000 I've never had to tweak anything for consistency. There are days when atmospheric conditions will effect the flight path enough to throw the data off, but I generally understand that when things are off, its an error on my part. Having said that, I don't know what app you run but Stelock, ab, and shooter have all proven to be excellent.
 

yobuck

Well-Known Member
Joined
Aug 23, 2008
Messages
1,757
Location
east central fl. /n.c. pa.
Accurate MV will give you a accurate rifle out to about 650 yards. Beyond that it requires a accurate BC. BC is best developed within 10% of the range at which your bullet goes transonic. When truing the BC if you are hitting high, raise the BC. If hitting low, lower the BC.
BC has to be developed for each barrel. Some may have the same BC, but not all.
Well uh uh isnt that what a dial on the scope is for?
Or do i live in a dream world?
 

david g ranes

Well-Known Member
Joined
Sep 9, 2009
Messages
580
I have a mag and lab for velocity checking. Both excellent. Out to 1000 I've never had to tweak anything for consistency. There are days when atmospheric conditions will effect the flight path enough to throw the data off, but I generally understand that when things are off, its an error on my part. Having said that, I don't know what app you run but Stelock, ab, and shooter have all proven to be excellent.
I’m using geo ballistic arc which is supposed to be a decent app it’s just weird I have trouble with this one and never had issues with gunwerks app I’m sure I’m goofing up something just trying to figure it out because my poi has never been off as much on what the app is telling me to dial. David
 

BrentM

Well-Known Member
Joined
Jan 10, 2013
Messages
3,094
Location
Meridian, Idaho
I’m using geo ballistic arc which is supposed to be a decent app it’s just weird I have trouble with this one and never had issues with gunwerks app I’m sure I’m goofing up something just trying to figure it out because my poi has never been off as much on what the app is telling me to dial. David
I had that app too and I don't like it. I used it a lot at first, especially the wind segmenting function but it drove me nuts. Just my opinion, but I would suggest shooter or strelock Pro. I like shooter from a simplicity sake. To me, it's very intuitive compared to other app with a lot of unnecessary complexity.
 

david g ranes

Well-Known Member
Joined
Sep 9, 2009
Messages
580
I had that app too and I don't like it. I used it a lot at first, especially the wind segmenting function but it drove me nuts. Just my opinion, but I would suggest shooter or strelock Pro. I like shooter from a simplicity sake. To me, it's very intuitive compared to other app with a lot of unnecessary complexity.
Did you feel the figures that it put out was correct compared to your other app you have used I don’t have trouble inputting my info but it just seems my dial up at farther ranges always leave me shooting high compared to my velocity inputs and haven’t had that happen until I bought this app. David
 

BrentM

Well-Known Member
Joined
Jan 10, 2013
Messages
3,094
Location
Meridian, Idaho
Did you feel the figures that it put out was correct compared to your other app you have used I don’t have trouble inputting my info but it just seems my dial up at farther ranges always leave me shooting high compared to my velocity inputs and haven’t had that happen until I bought this app. David
The data didn't line up with kestrel or shooter and real life. I have had no issues being on target with kestrel and shooter. Both use the same basic ballistic engine. Applied Ballastics is really hard to beat for normal ranges. If you get into ELR you will need 6dof and custom drag curve data. I just struggled with ARC and Ballistic AE. I deleted both Apps and use my kestrel and shooter. For hunting I have leica 3200's and the data from them match's shooter and kestrel to 1000. Past 1000 kestrel links to the leica so it's applied ballistics data.
 

david g ranes

Well-Known Member
Joined
Sep 9, 2009
Messages
580
The data didn't line up with kestrel or shooter and real life. I have had no issues being on target with kestrel and shooter. Both use the same basic ballistic engine. Applied Ballastics is really hard to beat for normal ranges. If you get into ELR you will need 6dof and custom drag curve data. I just struggled with ARC and Ballistic AE. I deleted both Apps and use my kestrel and shooter. For hunting I have leica 3200's and the data from them match's shooter and kestrel to 1000. Past 1000 kestrel links to the leica so it's applied ballistics data.
Here I thought I was getting a good app but with the other ones I have used I might have been a click off but with this one it seems 1 moa off is the norm. David
 

Recent Posts

Top