Significant dope change help

[Ohioguy47]

Howdy folks. Just looking for a little help diagnosing a dope change.

I usually hold 3.9m at 600. Today it was consistently 4.4m. I would expect maybe a .1 shift with different weather conditions at this range. Not a whole half mil

Rifle: bmp 6.5 creed. Everything snuggled down to spec. Pic rail is bedded on.

Handloads: h4350, hornady 140bthp. Powder and bullets are different lots than last time, but chronographed velocity remained the same despite colder temperatures.

Scope: just swapped to a trijicon tenmile. Put it in my tall target vice and it consistently tracked. Both were in the same height nightforce rings.

All in all I'm not sure what the hell would cause it. Winds were insignificant. No major pressure changes. If anyone has something to point to I'd appreciate the insight.

 

[waveslayer]

Tagging to follow for curiosity reasons. But my guess is switching the scope... since that's you're only stated variable.

Is the scope mounted in the same location? Maybe both scopes didn't truly track thus the significant shift in 3.9 to 4.4 mils in addition to mirage perhaps . I've seen mirage change some dope...

 

[Feniks Technologies]

Assuming that you checked the zero on the rifle and it was the same.......your new lot of bullets might have a lower BC than the last.

In all likelihood, its several small things adding .1 here and .1 there.

 

[Ohioguy47]

Tagging to follow for curiosity reasons. But my guess is switching the scope... since that's you're only stated variable.

Is the scope mounted in the same location? Maybe both scopes didn't truly track thus the significant shift in 3.9 to 4.4 mils in addition to mirage perhaps . I've seen mirage change some dope...

That's what I was thinking too, but it's so odd that it didnt have any tracking issues when I tested with almost a half hour straight. Rings are in same location but with the scope moved back closer to my eye. I can see this causing some minor shift. Thanks

 

[Ohioguy47]

Assuming that you checked the zero on the rifle and it was the same.......your new lot of bullets might have a lower BC than the last.

In all likelihood, its several small things adding .1 here and .1 there.

Zero was solid. I can see that adding a .1 or .2. Thanks!

 

[Steel head]

Powder lots can vary dramatically especially if factoring in humidity change from an open can to fresh.
I’ve seen a 75 fps change in lots with H4350.
Bullets also can vary a bit from lot to lot.

Add in environmentals and who knows.

Check your speeds
Re true your solver.
Compares notes from other days with similar environmentals.

 

[Barelstroker]

Powder lots can vary dramatically especially if factoring in humidity change from an open can to fresh.
I’ve seen a 75 fps change in lots with H4350.
Bullets also can vary a bit from lot to lot.

Add in environmentals and who knows.

Check your speeds
Re true your solver.
Compares notes from other days with similar environmentals.

I'm inclined to agree with the moisture content of the powder.
A couple guys did some testing with what I considered to be astounding differences in velocity between different moisture levels.
Good call Steel head.

 

[Baron23]

I thought he said speeds remained consistent…he said he chrono’d and got the same MV.

 

[rijndael]

Was your parallax properly adjusted?

 

[nn8734]

I thought he said speeds remained consistent…he said he chrono’d and got the same MV.

Correct, he did say that. I’ve seen .3- .5 difference when DA drops by 3000 or so at 600m-1000m with my 6.5cm. Colder moister air will slow it down requiring more elevation all other things equal.

Question is how much colder was it today or whenever he last shot it vs when his dope was recorded previously. And if he shot it this morning vs later in the day last time (always more humid in the am before the sun dries the air out over the course of the day.

Interesting…

 

[Barelstroker]

I thought he said speeds remained consistent…he said he chrono’d and got the same MV.

So he did. Ahhh, maybe not the powder.

 

[ShtrRdy]

Correct, he did say that. I’ve seen .3- .5 difference when DA drops by 3000 or so at 600m-1000m with my 6.5cm. Colder moister air will slow it down requiring more elevation all other things equal.

Question is how much colder was it today or whenever he last shot it vs when his dope was recorded previously. And if he shot it this morning vs later in the day last time (always more humid in the am before the sun dries the air out over the course of the day.

Interesting…

If I read correctly you're saying more humidity means the air is denser? If so, that's not true. Humid air is less dense.

 

[Ohioguy47]

Replaced the optic and chassis with an amg and xlr, respectively. Tested 100% tracking.
Confirmed zero and velocity.
Still am having the dope be 4.4m up at 600 yards.
Ballistic solvers are saying 3.8 to 4m at that range. Would have to take well over 100fps off my MV to true at that distance or remove over 1.2 off my G1 Bc . All atmospheric conditions are entered correctly.
Rifle is shooting great at that distance with 3 inch groups. I'm having a having trouble believing the barrel is jacking my BC up that badly.
Yes parallax is correct and my fundamentals aren't too terrible.
I'm really dang confused. Would hate to dump an affordable rifle that groups well and has a smooth action.
One of you wealths of knowledge please help me out and end my pain.

 

[Barelstroker]

Replaced the optic and chassis with an amg and xlr, respectively. Tested 100% tracking.
Confirmed zero and velocity.
Still am having the dope be 4.4m up at 600 yards.
Ballistic solvers are saying 3.8 to 4m at that range. Would have to take well over 100fps off my MV to true at that distance or remove over 1.2 off my G1 Bc . All atmospheric conditions are entered correctly.
Rifle is shooting great at that distance with 3 inch groups. I'm having a having trouble believing the barrel is jacking my BC up that badly.
Yes parallax is correct and my fundamentals aren't too terrible.
I'm really dang confused. Would hate to dump an affordable rifle that groups well and has a smooth action.
One of you wealths of knowledge please help me out and end my pain.

What ballistic solver you using?

 

[rijndael]

Have you box tested your scope?

 

[dutchboy53]

Replaced the optic and chassis with an amg and xlr, respectively. Tested 100% tracking.
Confirmed zero and velocity.
Still am having the dope be 4.4m up at 600 yards.
Ballistic solvers are saying 3.8 to 4m at that range. Would have to take well over 100fps off my MV to true at that distance or remove over 1.2 off my G1 Bc . All atmospheric conditions are entered correctly.
Rifle is shooting great at that distance with 3 inch groups. I'm having a having trouble believing the barrel is jacking my BC up that badly.
Yes parallax is correct and my fundamentals aren't too terrible.
I'm really dang confused. Would hate to dump an affordable rifle that groups well and has a smooth action.
One of you wealths of knowledge please help me out and end my pain.

Who do want to believe your rifle or the ballistic solver?
look at weaponized math
you do it with the paper targets and then adjust the solver
paper doesn't lie

 

[nn8734]

Replaced the optic and chassis with an amg and xlr, respectively. Tested 100% tracking.
Confirmed zero and velocity.
Still am having the dope be 4.4m up at 600 yards.
Ballistic solvers are saying 3.8 to 4m at that range. Would have to take well over 100fps off my MV to true at that distance or remove over 1.2 off my G1 Bc . All atmospheric conditions are entered correctly.
Rifle is shooting great at that distance with 3 inch groups. I'm having a having trouble believing the barrel is jacking my BC up that badly.
Yes parallax is correct and my fundamentals aren't too terrible.
I'm really dang confused. Would hate to dump an affordable rifle that groups well and has a smooth action.
One of you wealths of knowledge please help me out and end my pain.

The bullet’s impact at whatever elevation is all that counts. The other consideration is that your previous optic had clicks that were prouder than the current optic or current optic is not as. Doesn’t matter. All that matters is that its repeatable over subsequent sessions in similar conditions as currently configured.

Shoot again in similar conditions (same ammo produced with same components from same lots) in the near future to be sure your validation youve done still holds true

 

[CShooter92]

What ballistic solver are you using and what speed are you getting from your chronograph?

I had a buddy whose dope was off by about 0.4-0.5 mil past 600 yards simply because he had his sight height entered wrong in his kestrel. Make sure that's correct as well.

 

[JBoomhauer]

Dumb question, Are you shooting at the same range as before? Is it possible the target was moved?

I shoot one range that has a F-class type 600yd firing line that is actually 580 or so . It took quite a while to figure out why my data was always a little off at this range.

Kept hearing stuff like updraft as a reason between regulars.

 

[CavReconScout]

You true the ballistic program to the rifle, not the other way around.

 

[huntnh]

I agree probably a combination of different powder and temp Iv seen up to 100fps difference in powder lots. Barrels loose speed when there almost done what’s your round count?

 

[CK1.0]

In this case, since you chrono'd it the first time and got 3.9m and then later got the same MV number but it took 4.4m, I'd ignore the chronograph number, get on at 500 the old fashioned way, and then true up your velocity using a ballistic calculator. After doing that, I'd try 300/400/600 with whatever MV the calculator spits out. BC might affect 600 a little, but not .5m, closer in, BC shouldn't come into play too much, so I would just use whatever generic BC number Hornady puts on the box for this.

If you're on, then you'll know your chronograph is a liar. At least you'll have one less variable.

First things first, recheck that you entered all your initial rifle info correctly and didn't bump or screw something up (twist, hight over bore, etc), and recheck your zero. AMHIK...

@huntnh might be on to something though... dead barrel would do it.

Half a mil is a bunch though, so if the chrono isn't broken, and your barrel ain't dead... you're definitely shooting over a buried alien space ship that is increasing gravity's pull between you and the target.

 

[Billdoe708]

Dumb question your range finder didn't get switched between yards and meters did it?

 

[NoDopes]

Is your new scope in MOA?

Can you try another lot of powder/bullets just to check and compare?

I thought colder air was more dense, but higher altitude is less dense so they can generally cancel each other out when shooting in higher elevations.

 

[bax]

You said, "I usually hold 3.9m at 600. Today it was consistently 4.4m." What was the temperature when you were dialing 3.9? What was the temperature when you were dialing 4.4? As air cools it becomes more dense and imposes more drag on the bullet - as the temp drops you have to dial more. Also, if I recall correctly, dry air is more dense than humid air. Last Sunday I was shooting a 308 from 100 to 1k. My dope card was based on good gun data measured at about 75F. My card told me 11.0 mils at 1k. On Sunday, I needed 12 mils to make point-of-aim hits. So 40F temperature delta gave me a whole mil at 1k. I was shooting in northern Indiana, your handle says Ohio. It was chilly on Sunday. Could that explain what you saw?

 

[RegionRat]

OP's change at 600 yards is more than double the normal change from climate/pressure errors, so hard to say why.

May not matter if the dope is stable, but I agree it is a little troublesome that your BC would be that depressed to fit the dope.

In the end, as long as the accuracy is good, it is the stability and predictability that counts.