What variable to change when truing my weapon

[seidersjoden]

Hi,

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. Some people lean toward changing the MV over the BC when truing a weapon or vice versa. So my question is, if I do a good chrono of a weapon and take as many variables as I can out of the inputs I put into my Kestrel Atrag, which one should I change when truing the weapon to match the scope value?

Thanks,
Joden

 

[Keith Glasscock]

With the op's claim of being active duty military spec ops sniper, I find my advice to be truly insulting to anyone of that skill level. Therefore, my post is removed and replaced with this apology.

Sorry, I can't help you. I know nothing more than you should have learned in your training.

 

[Erik Cortina]

Donovan, I think the OP is talking about matching the rifle trajectory with a ballistic program by changing certain parameters, such as BC, bullet weight, and speed.

 

[BoydAllen]

Seidersjoden,
I think that we have a couple of issues here. First of all, where are you located, generally, and what is your shooting experience? The way that you asked your questions leads me to believe that we have some basic experience and word definition issues here. What sort of rifle or rifles do you shoot, at what distances, with what consistent accuracy? Do you reload ammunition? Understand that I am no trying to be difficult, but I think that we need to know more about what your level of experience is in order to do a better job of helping you.

 

[Erik Cortina]

Eric -

That is exactly my thoughts as well. I wrote my reply in context to the word "truing" as it is used in modern riflery, in hopes it does not get used in slang, to what it isn't.

D

I see, and I agree with you.

 

[Immike]

Hi,

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. Some people lean toward changing the MV over the BC when truing a weapon or vice versa. So my question is, if I do a good chrono of a weapon and take as many variables as I can out of the inputs I put into my Kestrel Atrag, which one should I change when truing the weapon to match the scope value?

Thanks,
Joden

I see what you are asking...
With everything properly entered in the program, I change the velocity to satisfy the impact at the furthest you can shoot accurately.

 

[seidersjoden]

Seidersjoden,
I think that we have a couple of issues here. First of all, where are you located, generally, and what is your shooting experience? The way that you asked your questions leads me to believe that we have some basic experience and word definition issues here. What sort of rifle or rifles do you shoot, at what distances, with what consistent accuracy? Do you reload ammunition? Understand that I am no trying to be difficult, but I think that we need to know more about what your level of experience is in order to do a better job of helping you.

Boyd,
I am an active duty sniper in spec ops and avid elk hunter, that being said my experience with extending long range (apart 1100yards) is limited and I just got a 30-378 made from GAP that Im going to use for extending long range shooting/hunting. I realize to stay within lethality specs for humane hunting shots bullets need to have be traveling at least 1700fps so please don't question my good intentions in that category. I'm glad you asked for more details from me so you can better help me out as I'm sure you have more experience with longer distances than myself. So for humane kills my 30-378 with 230g Begers put me at 1400y while retaining at least a MV of 1700fps at the furthest. My question is, when I take my rifle out to true it using the kestrel with Atrag or my iPhone with Ballistics A.E. app, I am told to sight the gun in at 100y then shoot at the furthest comfortable distance that my skills allow me in order to develop a consistent group to base my ballistics off of. Once I make a good group whether its high or low, what should I adjust, MV or BC, or a bit of both (which some people recommend).Bryan Litz says in his latest book that you want to shy away from changing the BC when truing the dope because that could compromise other distances. In My community, we use Atrag Kestrels and we teach to change the MV also. Any experience or recommendations?

 

[seidersjoden]

I see what you are asking...
With everything properly entered in the program, I change the velocity to satisfy the impact at the furthest you can shoot accurately.
[/quote]

Thanks for the help

 

[Erik Cortina]

Ok, just to be clear, you are not "truing" your gun, you are "calibrating" your gun to match your drop table.

 

[Drop Port]

With all other variables adjusted, fudge the FPS to get it to run true to your real fire.


dmoran you might be surprised to find out how little is given to some who need it most, a lot of guys run off a FDAC card in the field. Then again shooting is only part of the job

 

[seidersjoden]

I apologize, it was ft-lbs of energy not MV on order to get bullet spread for humane kills. Either way we are typically giving the latest technology but it doesn't mean we have the latest experience in using that technology. Like anything you can always learn more and I know you guys have more experience with long range shooting because it's a lifestyle. Unfortunately if I had it my way I would focus on long range tactical work but there are other skill-sets to be kept up too. The Atrag we use now is much better than the Cheytach software we used 5 years ago but we are taught to only change the MV because the ammo we get for the 300w has a BC that isn't as consistent. That being said since this is personal use I want to learn the correct way to make adjustments. Any thoughts?

 

[Immike]

I used to field shoot steel with a (police tactical) fellow. At all times we watched for live targets (ground hogs) while we shot a game we called rotation. When they did appear he would fumble around with his notes while I killed them. For hunting you will need to be familiar with the rifle and have your homework done before the hunt. Build a drop sheet in simple, easy to read, uncomplicated notes. I had everything I needed on a card inside my flip cap on the scope. I just need the distance to the target. Good luck.

 

[BoydAllen]

So this question is not about tuning a load, or a rifle for best performance, but rather how to adjust the variables of a external ballistics program so that it is a better predictor of what the scope adjustments need to be for a given long range shot?

 

[mikecr]

It appears to me that with an unknown ballistic error -MV adjustment- recovers with least deviation from an accurate (baseline) path throughout the distance.

I used a ballistic spreadsheet to goal seek for solutions to errors in BC, scope height, slope, air density, and zero, with BC adjustment -vs- MV adjustment, and then differentiated path from baseline at 250yd increments.
While certain errors can be directly countered for, like BC adjustment directly counters air density, MV adjustment still works pretty well, even while inappropriate. Otherwise, MV was a very good adjustment with other errors and smaller errors in a spread combining.

This seems unintuitive to me, as I know my MVs and all other parameters as measured -except BC. I have to calculate BC and then validate my results.
This has worked so far without fudging of MV.
Then again, I don't shoot beyond a killzone covered by 1/4moa of system accuracy,, which for me is ~600yds on groundhogs.

Someone mentioned cal checking your scope. This is vital.
If you dial, do not assume or generalize your scope adjustments. Test and take them to their true IPHY value per click, and set this in your software.

 

[seidersjoden]

So this question is not about tuning a load, or a rifle for best performance, but rather how to adjust the variables of a external ballistics program so that it is a better predictor of what the scope adjustments need to be for a given long range shot?

Yes, I had heard when you truing (and yes truing is used by Bryan Litz in reference to adjusting ballistics to match Dope at ranges so I figure I wouldn't be too awfully wrong by using this term) a rifles dope at ranges to adjust MV or BC.

 

[seidersjoden]

It appears to me that with an unknown ballistic error -MV adjustment- recovers with least deviation from an accurate (baseline) path throughout the distance.

I used a ballistic spreadsheet to goal seek for solutions to errors in BC, scope height, slope, air density, and zero, with BC adjustment -vs- MV adjustment, and then differentiated path from baseline at 250yd increments.
While certain errors can be directly countered for, like BC adjustment directly counters air density, MV adjustment still works pretty well, even while inappropriate. Otherwise, MV was a very good adjustment with other errors and smaller errors in a spread combining.

This seems unintuitive to me, as I know my MVs and all other parameters as measured -except BC. I have to calculate BC and then validate my results.
This has worked so far without fudging of MV.
Then again, I don't shoot beyond a killzone covered by 1/4moa of system accuracy,, which for me is ~600yds on groundhogs.

Someone mentioned cal checking your scope. This is vital.
If you dial, do not assume or generalize your scope adjustments. Test and take them to their true IPHY value per click, and set this in your software.
[/quo!

1) If you find the scope doesn't track perfectly with MOA is it easier to use IPHY?

2) So are you saying you adjust the MV or the BC at longer distances? Or you adjust what you know the least amount about like the BC??

Thanks
Joden

 

[mikecr]

1) If you find the scope doesn't track perfectly with MOA is it easier to use IPHY?

Yes. IPHY provides high resolution. For example 1moa = 1.047197551 IPHY. Your expensive scope, merchandised as MOA, or MIL, probably isn't.

2) So are you saying you adjust the MV or the BC at longer distances? Or you adjust what you know the least amount about like the BC??

Personally I set every parameter as measured. Scope height crosshair to bore centerline, slope from a plumb ACI, absolute pressure, temperature and relative humidity from a sea level cal checked Kestrel, Lattitude from GPS, bearing from a compass, MV from an Oehler chronograph, laser ranged zero/distances, elevation adjustment set plumb.
Then I add software calculated BC (based on bullet measure), and shoot on distant targets to validate my solutions. If needed, I would tweak BC at this point given that all else is measured.

Anyway, what I was suggesting is that adjusting MV for errors does appear sound to me based on scenarios I ran in software.
But I have never needed to do so, and haven't tried it myself.

 

[seidersjoden]

Huge help, thanks a lot Mike, Im considering doing the IPHY now. Just to be clear, by using absolute pressure aren't making the elevation irrelevant which is important to account for? I know that Station pressure is pressure at your actual location which is what you want.

 

[338 Mollett]

This is the kind of R&D I have done for 5 years on these calibers,I think I can help PM on the way.

 

[seidersjoden]

This is the kind of R&D I have done for 5 years on these calibers,I think I can help PM on the way.

Would love to hear any info on loads and ballistic truing at long range experience you have.

Joden