Dope inconsistancy

[Canadian Bushman]

Given you scope is OK, and there are no conditions like wind effecting the trajectory, I would expect the answer lies in the BC/velocity settings. The only problem is that it would take a fairly large adjustment to the BC to effect the amount that you are off at 500 yards. The issue is more likely an error in both BC and velocity. The Berger/Litz BC's are generally accurate and would unlikely require the amount of correction to bring your 500 yard impact down. Having had a similar issue a few years ago I found that I solved the problem by first recording the current dopes. Next, adjust your velocity in the ballistic program, in your case, higher so your impact at 500 yards is corrected. Your program will now show your 700-1000 yards dopes low. Now adjust your BC lower to try and replicate the values of your original dopes for the longer ranges. I may take some trial and error. IMO

This is something ive considered, the only thing that bothers me is that shooting over my chrono yeilds velocities that work out really close to my dope. So im not sure where to start.

 

[Broz]

This is something ive considered, the only thing that bothers me is that shooting over my chrono yeilds velocities that work out really close to my dope. So im not sure where to start.

what chronograph are you using?

I think I would move to 700 or 800 yards and shoot 2 or 3 groups letting the barrel cool and see what that yields for sure.

At 500 is it just cold bore shots going high or is this a center group measurement?

Jeff

 

[Canadian Bushman]

what chronograph are you using?

I think I would move to 700 or 800 yards and shoot 2 or 3 groups letting the barrel cool and see what that yields for sure.

At 500 is it just cold bore shots going high or is this a center group measurement?

Jeff

Im using a beta chrony thats been shot twice so i have no problem throwing out data i recieve from it, i just think the fact that it matches so much of my data is more than coincidence.

My cold bore shot is eerily consistent with rifle always grouping very well with subsequent shots.

Just two weeks ago i shot a 3" 3 shot group centered on point of aim at 741yds with this same load, using load and weather conditions in shooter.

Last week i shot two feral hogs at 635yds and the bullet hit about 2-3" from point of aim, again with shooter plotting conditions.

This tuesday i got a second round hit at 910yds that was 6" high again with shooter.

And this is also the load that i use for 1k yd ftr, and always lands between 36-37 moa for the entire string at the range shooting due north. And we typically fire 60 rounds a match.

 

[Canadian Bushman]

My chrony does tend to give me readings about 10-20 fps faster then the mv that works in shooter, but at the ranges i shoot most and the average accuracy im able to hold this difference doesnt account for much.

My average es for this load is around 20 to 25 fps.

 

[Canadian Bushman]

Are you using a G1 or G7 BC, are you on out to a 1000 yards?

Im using the G1 bc. Ive run the same data with the G7 and its identical.

 

[Broz]

Well you already know the data from a shooting chrony is questionable. As is true with the 3 I own. But this still does not answer the question of why 5" high at 500 and spot on at 750? I am just thinking and asking questions that come to mind. If your 500 yard data is center group and not cold bore it eliminates the barrel stress, stock and bedding idea's. I truly feel there is a glitch somewhere. You stated it is not in scope tracking so I am at a loss. But we have all set up many rifles, I would like to know for sure why this one is off a full moa at only one distance.

Do you have the powder temp data area of the program zeroed? I have seen some wrecks from bad data there.

If I come up with an idea I will post again.

Jeff

 

[Canadian Bushman]

Well you already know the data from a shooting chrony is questionable. As is true with the 3 I own. But this still does not answer the question of why 5" high at 500 and spot on at 750? I am just thinking and asking questions that come to mind. If your 500 yard data is center group and not cold bore it eliminates the barrel stress, stock and bedding idea's. I truly feel there is a glitch somewhere. You stated it is not in scope tracking so I am at a loss. But we have all set up many rifles, I would like to know for sure why this one is off a full moa at only one distance.

Do you have the powder temp data area of the program zeroed? I have seen some wrecks from bad data there.

If I come up with an idea I will post again.

Jeff

Temp data isnt completely ironed out, and could be questioned but i have been narrowing it down this last year and feel im getting very close.

My problem here is in shooter the temperature variation is linear and im not sure the relationship between velocity change and temp is linear. So i dont know how close is as close as ill be able to get.

There are a few things i dont understand and have in question. Perhaps they could be related to my problem.

Bullet B.C. In relation to MV - ive always trusted bergers published B.C., dont know any better.
Scope height - measuring on canted base
Copper fouling - rifle seems to shoot high (faster) as fouling increases - obvious in rising zero over 70-100 shots.
Factory Barrel - very rough, and copper fouls quickly.
Semi-New Nighforce nxs - seems to track and hold zero identically to last nightforce, but im always suspicious.
Shooter error - im currently struggling with consistancy in trigger control, shouldering the rifle the same with equal pressure, controlling recoil the same way each time i shoot, and managing my reloads to shoot consistent MV, ES, and accuracy.

 

[Broz]

Temp data isnt completely ironed out, and could be questioned but i have been narrowing it down this last year and feel im getting very close.

My problem here is in shooter the temperature variation is linear and im not sure the relationship between velocity change and temp is linear. So i dont know how close is as close as ill be able to get.

{Take a dial up reading for the 500 yard shot then zero out MV temp variation and see if it comes in with less dial up.}

There are a few things i dont understand and have in question. Perhaps they could be related to my problem.

Bullet B.C. In relation to MV - ive always trusted bergers published B.C., dont know any better.
{ I agree to start with advertised BC}

Scope height - measuring on canted base
{ I measure center bore to center scope at turret location}

Copper fouling - rifle seems to shoot high (faster) as fouling increases - obvious in rising zero over 70-100 shots.
Factory Barrel - very rough, and copper fouls quickly.
Semi-New Nighforce nxs - seems to track and hold zero identically to last nightforce, but im always suspicious.

Shooter error - im currently struggling with consistancy in trigger control, shouldering the rifle the same with equal pressure, controlling recoil the same way each time i shoot, and managing my reloads to shoot consistent MV, ES, and accuracy.
{ all of these last ones go back to , if on at 750 should be on at 500 but a good reason to gather data from at least 2 or 3 shot groups}

Inserted comments in bold
Jeff

 

[Canadian Bushman]

Ive been playing with my data in shooter all morning. If i add about .3-.4 to scope height the "bump" around 500yds starts to come in a bit. If i lower my bc from .281 to .275 and drop MV to 2565 from 2580 things get even closer. Probably within .25 moa from my actual data. Seeing how its a .5 moa gun thats pretty close.

My scope height at the turret is actually about 2.1-2.2
Shooter comes in at about 2.4-2.5

My close range data is closer with the low scope height and long range data is closer with the high scope height.

Could this have something to do with the way the erector tube is positioned in the scope body across my range of data?

 

[royinidaho]

From your pics I'll not be going too far out on a limb by offering that wind and topography are not the problem.

Jeff and yourself are headed in a good direction.

I think we all will learn something when this gets resolved.

 

[WildRose]

Are you measuring your scope height from center of the bore to center of the tube?

 

[Canadian Bushman]

Broz,
The difference between dial up for powder temp of that day and dial up without factoring powder temp is only about .1, it was about 60 deg saturday.

Do you normally have to tweak bc to match up your data?
Ive never made habit of it, but you shoot much much further than i do with far greater accuracy.

Roy,
Yes the terrain here is quite flat, and the wind is usually pretty consistent as far as direction is concerned.

Wild rose,
I have been measuring center of bore to center of tube at the turrets like broz described, i was just uncertain if this was the right way to do it as i never asked anyone.

I dont like having false data to make things mesh but ill put up with it if it works.
Im gonna go over the rifle and check all my bolts, clean the bore, fire a bunch of fouling shots then try to collect data from 300,500,700, and 900 all in one day to get a good plot against my two current sets of drops. Right now that cool front just blew in so its insanely windy and cold. Might have to wait til the weekend. Thank you guys for your ideas and advice, as always its very much appreciated.

 

[WildRose]

Broz,
The difference between dial up for powder temp of that day and dial up without factoring powder temp is only about .1, it was about 60 deg saturday.

Do you normally have to tweak bc to match up your data?
Ive never made habit of it, but you shoot much much further than i do with far greater accuracy.

Roy,
Yes the terrain here is quite flat, and the wind is usually pretty consistent as far as direction is concerned.

Wild rose,
I have been measuring center of bore to center of tube at the turrets like broz described, i was just uncertain if this was the right way to do it as i never asked anyone.

I dont like having false data to make things mesh but ill put up with it if it works.
Im gonna go over the rifle and check all my bolts, clean the bore, fire a bunch of fouling shots then try to collect data from 300,500,700, and 900 all in one day to get a good plot against my two current sets of drops. Right now that cool front just blew in so its insanely windy and cold. Might have to wait til the weekend. Thank you guys for your ideas and advice, as always its very much appreciated.

I missed where Broz had mentioned it. He is of course correct. One caveat, if you have a canted base that could explain why when you adjusted it your dope seemed to fit better.

 

[Broz]

Broz,
The difference between dial up for powder temp of that day and dial up without factoring powder temp is only about .1, it was about 60 deg saturday.

Do you normally have to tweak bc to match up your data?
Ive never made habit of it, but you shoot much much further than i do with far greater accuracy.


I dont like having false data to make things mesh but ill put up with it if it works.
Im gonna go over the rifle and check all my bolts, clean the bore, fire a bunch of fouling shots then try to collect data from 300,500,700, and 900 all in one day to get a good plot against my two current sets of drops. Right now that cool front just blew in so its insanely windy and cold. Might have to wait til the weekend. Thank you guys for your ideas and advice, as always its very much appreciated.

Here is what I will suggest. Zero the MV / Temp variation completely. This is something I am working on but have yet to get it to work to my advantage. However I think with enough testing and data it could be of help. Problem is the chamber temp is going to change this so I feel it will be only good for a first round cold bore where the rifle and ammo have had time to acclimate to the ambient temp. Can you see where the most temp stabile powders, with less velocity could be very important to induce less error? So for now zero out that data to make it inactive. I have seen it do more harm than good if not used under perfect circumstances.

I won't use false data either. Use the 2.1 or 2.2 scope height and factory BC for now. We already know low end chronographs lie so this is a variable and I feel where we should work especially with only slight changes as you said helped.

Your check list and shooting plan is a good one. Drops under like field conditions will be great to work with.

Start with a cold bore zero check. Remember a100 yrd zero off by 1/2 to 3/4 " will result in drops being off by .5 to .75 moa. Test and reconfirm here cold bore.

You also bring up a good point, we are working inside a .5 moa rifle, ammo and shooter skill zone. The reason we shoot 2 or 3 shot groups with cool time to proof test.

If you get a calm day that is overcast go for it. Mirage has sent me home from many days confirming drops. Even the slightest mirage will kill your efforts. I remember the last time this happened to me. I was 1 moa off at 1000 yds. center group. I said BS and went home. The next day with no mirage the same dope same target was spot on.

Also, don't ignore the scope turret value calibration adjustment in the shooter app. It is your friend. It is very critical to find a slight error in scope tracking. Some times at 100 yards it is impossible to find. But as you crank up it multiplies. So if inserting a correction factor of (example) .985 or 1.025 or so on gets you there it could be revealing a hidden tracking issue you can not detect. This is a golden tuning aid for this app.

But first you need solid recorded drops for different distances along with solid recorded field conditions. Then sit down with a cup of coffee in the evening and make the app match the rifle.

Jeff