What Variable to Change When Truing My Rifle at Extending Ranges

[Joden]

Hi Bryan,
When doing the truing process I have heard different opinions. Some say after sighting the gun in at 100y then shooting out at 900-1300y or whatever range you can consistently hit targets at, if the group is high or low to adjust the MV. Some say if I have Chronograph the gun and feel confident in the MV that I should change the BC. By the way I’m shooting the 230 Target Hybrids. Since I know you have done a great deal with insuring the BC's on Berger bullets are good I trust in fairly accurate BC measurements given your experience. Also, I have read both your Applied Ballistics for Long Range Shooting and the Accurate and Precision for Long Range Shooting. The latter book stated that a shooter needs to be careful what they choose to change when truing, it seemed you leaned toward changing the MV over the BC when truing a weapon. So my question is, if I do a good chromo of a weapon and take as many variables as I can out of the inputs I put into the Kestrel, which one should I change when truing the weapon?

Thanks for your time,
Joden

 

[WaltHer]

I'm not Bryan, but I seem to remember him suggesting changing whichever variable you have the least amount of confidence in. If you're using the G7 bc's in Applied Ballistics, and have read the section about the pitfalls of chronograph use, then I think the answer is somewhat self evident. My second suggestion is to true your program at the distance where ballistics program predicts your projectile is going transonic instead of, "900-1300y or whatever range you can consistently hit targets at." This is made easier if you have some good data from a chronograph, but even soft data will get you close enough to aid you in truing.

 

[CoryT]

Start with small adjustments of the velocity. The chronograph numbers, no matter how 'good' your unit may be, have a certain degree of imprecision. It may be that is all that is required, but adjustments to velocity alone may not get the program to align well at all ranges. A small adjustment to BC may also be required. Adjustments to velocity of +/- about 5%, along with an adjustment of BC by 2% would not be out of line. More than that would cause me to be suspect about the data we are trying to match up, an incorrect range, an error in conditions or a group that is not actually where we think it is. One must be quite careful in collecting the data, lest you find yourself trying to get the program to give you an answer when you've actually asked the wrong question.

 

[Bigwheels]

I have found Bryans BC's to be very accurate. I am shooting the 230 hybrid targets with his .743 G1, & FFS. I have trued my program from sea level to 5600'asl. And have confirmed 1st rnd hits @ 1645yds, & 1511yds with it.
I used a method recommend by Blaine Fields. I first confirmed zero @ 100 then chrony'd the load. Use the velocity obtained to get a solution for 350-400yds. Shoot a group at that range, & adjust the MV to bring the sution to the poi. Then move out to just shy of trans-sonic range to verify the trajectories. If they don't match then adjust the BC. This is the method recommend by the maker of FFS, & it does work.

 

[Joden]

Thanks for the info guys.

I have found Bryans BC's to be very accurate. I am shooting the 230 hybrid targets with his .743 G1, & FFS. I have trued my program from sea level to 5600'asl. And have confirmed 1st rnd hits @ 1645yds, & 1511yds with it.
I used a method recommend by Blaine Fields. I first confirmed zero @ 100 then chrony'd the load. Use the velocity obtained to get a solution for 350-400yds. Shoot a group at that range, & adjust the MV to bring the sution to the poi. Then move out to just shy of trans-sonic range to verify the trajectories. If they don't match then adjust the BC. This is the method recommend by the maker of FFS, & it does work.

Ill be putting all these methods to work I'm sure. One question, what does FFS stand for? I wonder why only shooting at 350-400 yards for truing works well, maybe it has to do with the ability to shoot a confident group at that range and having better data to go off of than trying to collect a solid group at 1300yrds. Any purpose for that over truing at transonic ranges a=instead of 350-400yards?

Thanks
Joden

 

[Bigwheels]

Basically with this procedure you are trueing the MV only @ 350-400 because at those ranges the BC matters very little but MV matters much more. In other words if you're poi is off by 2" @ 400yds a huge change in BC is required to adjust it to match but a small change in MV will do it. Then once you have the MV down any error @ long range must be incorrect atmospheric inputs or incorrect BC. ASSUMING the rifle is driven properly. Like has been said previously any adjustment more than a few % one way or the other is probably incorrect. And don't expect a cheap Shooter app to be accurate enough to work at both long, & short range, & low/high elevation. It won't do it. I have tried several times. That is why I use FFS (Field Firing Solutions) for ELR work. I haven't used it but Cold Bore is reported to be as good. There was a thread on ballistic programs here some time ago. Search for it if you want.

 

[Joden]

Basically with this procedure you are trueing the MV only @ 350-400 because at those ranges the BC matters very little but MV matters much more. In other words if you're poi is off by 2" @ 400yds a huge change in BC is required to adjust it to match but a small change in MV will do it. Then once you have the MV down any error @ long range must be incorrect atmospheric inputs or incorrect BC. ASSUMING the rifle is driven properly. Like has been said previously any adjustment more than a few % one way or the other is probably incorrect. And don't expect a cheap Shooter app to be accurate enough to work at both long, & short range, & low/high elevation. It won't do it. I have tried several times. That is why I use FFS (Field Firing Solutions) for ELR work. I haven't used it but Cold Bore is reported to be as good. There was a thread on ballistic programs here some time ago. Search for it if you want.

Thanks Bigwheels, Ill look into FFS.

 

[wadcutter]

Shooter app is fine. It uses Velocity, BC and atmospherics etc. to come up with a solution just like any other program. Differences between programs are often just a result of rounding off errors in the program although there can be subtle differences as well. It is coincidence if these minor differences result in a better fit to a particular trajectory. You should not get gross differences between popular ballistic programs.

The problem I see with these programs is the data input. This includes the G7 data from Berger. This B.C. data is generally developed from shooting over distances up to 1000 yards, data beyond this is simply derived data with no real scientific testing to back up the theory.

In Bryan’s books he hints at custom drag curves being needed for accurate predictions for ELR shooting. This is another way of saying that the G7 data may or may not work at distances beyond what it was derived from.

For out to 1000 yards the G7 BC may be great but maybe a G6 or G8 BC might be a better fit for way out wide. The problem is that we don’t have G6 or G8 BC data or easy access to the programs to run it. This means that we are stuck using multi BC values past 1000 yards and these must be individually derived.

 

[Joden]

This means that we are stuck using multi BC values past 1000 yards and these must be individually derived.[/QUOTE]

There in lies my question, how do I develop a BC for ranges apart 1000y? Bryn did hint at that but if I remember correctly, unless I didn't retain that part he didn't go into detail about how to do that. Did he? To get your own BC you basically shoot a group out at the pre and post transonic range and then adjust the BC input in the ballistic program until it matches the actual come-ups on the scope? Is that right?

 

[wadcutter]

Joden,
That is basically it.
The numbers you derive will be ok for your rifle/scope/program, but may not be ok for someone else.
They need to come up with their own numbers as each rifle system is slightly different due to twist rates, scope turret errors etc.

 

[Bigwheels]

I agree the Shooter App is GTG. But only out to about 1000yds. I have tried everything including deriving my own multiple BC's with it to no avail. It will work well out to around 1000yds, but becomes inaccurate the farther out you go from there. I haven't read up on the mathematics of the different ballistic engines out there, but I know from 1st hand experience with 3 different bullets over the years in my 300WM that the one FFS uses is superior to the one the Shooter uses for beyond 1000yds. It doesn't even have a function for multiple BC's, & I have found it to be accurate from 0-2000yds @ both SL, & 6000'ASL, hot, or cold. I haven't had a chance to go higher yet, but am confident it would work @ 15,000'ASL as well as the bottom of Death Valley. Perhaps if I tried to adjust the multi-BC of Shooter again with the knowledge I've gained since then I could make it work, but I see no reason to try. FFS has given me 1st rnd hits on steel farther than a mile before as long as I do my part.( dope the wind right) I have been thinking of giving Patagonia Cold Bore a whirl lately, but haven't pulled the trigger yet. Low Light highly recommends it, & IIRC it's the one he uses in the field now. I understand it accounts for a few things better than FFS does, such as head/tail winds, & up/down angles. I'm reading up on it now. Perhaps Frank will chime in here.
Look at these.
http://www.snipershide.com/shooting...87296-pda-long-range.html?highlight=Cold+Bore
http://www.snipershide.com/shooting...ullet-test-phase-2-a.html?highlight=Cold+Bore

 

[DIBBS]

Thanks for the links Jeff.

 

[Bigwheels]

OOPS. Sorry. The XLR link is real cool, but not the one I thought it was. This one has way more on ballistic software.
http://www.snipershide.com/shooting...554-ballistic-program.html?highlight=software