Trajectory problem with Howa 6.5cm SWFA 3-9

[J Batt]

The trajectory is way off on my new rifle and scope.
Shooting a Howa Superlite in 6.5 creedmoor with a SWFA 3-9 scope. Both brand new. Using factory Hornady 140gr eldm.
Should be around 2600fps out of the 20” barrel. No chrono. Holds 1.5 MOA of accuracy. 100y zero.

Here’s my latest dope
75 degrees at 2500 feet, 27.5 inhg
1.8 mils at 360y
4.5 mils at 610y
At 2900ft 27 inhg it shot
6.6 mils at 760y.

This makes absolutely no sense with my calculator. I have to change the bc from what hornady states is .646 to .460 to make it line up at 760y. That’s insane. Or change the velocity to 2450fps which cannot be true. And either way I adjust the numbers the trajectory still wont line up at all yard lines.
Maybe the scope turret adjustments are off?

I have used this ammo in different rifle and scope combos and it’s always lined up very well with my calculator. So I know something is up, just not sure what.
Any ideas besides “did you tighten the rings”, would be appreciated.

 

[BAKPAKR]

I would start my troubleshooting by finding someone with a chronograph.

BTW - 147 ELDM gr factory ammo is about 2575 in my 22.4” Tikka. Advertised velocity is 2695. The 140 ELDM is listed at 2710.

 

[wind gypsy]

The trajectory is way off on my new rifle and scope.
Shooting a Howa Superlite in 6.5 creedmoor with a SWFA 3-9 scope. Both brand new. Using factory Hornady 140gr eldm.
Should be around 2600fps out of the 20” barrel. No chrono. Holds 1.5 MOA of accuracy. 100y zero.

Here’s my latest dope
75 degrees at 2500 feet, 27.5 inhg
1.8 mils at 360y
4.5 mils at 610y
At 2900ft 27 inhg it shot
6.6 mils at 760y.

This makes absolutely no sense with my calculator. I have to change the bc from what hornady states is .646 to .460 to make it line up at 760y. That’s insane. Or change the velocity to 2450fps which cannot be true. And either way I adjust the numbers the trajectory still wont line up at all yard lines.
Maybe the scope turret adjustments are off?

I have used this ammo in different rifle and scope combos and it’s always lined up very well with my calculator. So I know something is up, just not sure what.
Any ideas besides “did you tighten the rings”, would be appreciated.

Can you screenshot your data input?

I've clocked that ammo at 2600 out of 24" tikkas before but tikkas are usually slow. Possible you could be in the low 2500s if your barrel is as slow as a tikka.. a little above 2500 FPS and the listed AB BCs for that bullet and you'd be real close to the corrections you posted.

i'd say tall target test the Scope but probably takes a fair bit of shooting with a 1.5"+ cone to get good proof out of that.

 

[Formidilosus]

The trajectory is way off on my new rifle and scope.
Shooting a Howa Superlite in 6.5 creedmoor with a SWFA 3-9 scope. Both brand new. Using factory Hornady 140gr eldm.
Should be around 2600fps out of the 20” barrel. No chrono. Holds 1.5 MOA of accuracy. 100y zero.

Here’s my latest dope
75 degrees at 2500 feet, 27.5 inhg
1.8 mils at 360y
4.5 mils at 610y
At 2900ft 27 inhg it shot
6.6 mils at 760y.

This makes absolutely no sense with my calculator. I have to change the bc from what hornady states is .646 to .460 to make it line up at 760y. That’s insane. Or change the velocity to 2450fps which cannot be true. And either way I adjust the numbers the trajectory still wont line up at all yard lines.
Maybe the scope turret adjustments are off?

I have used this ammo in different rifle and scope combos and it’s always lined up very well with my calculator. So I know something is up, just not sure what.
Any ideas besides “did you tighten the rings”, would be appreciated.

That combo absolutely can be 2,450-2,500fps MV. I’ve seen several lot# that were at 2,500fps or just below from 20” barrels.

 

[J Batt]

Here’s what I started with before recording shots. The problem is, If I correct the velocity to match the 760y impacts (at 2440fps), then both 360y and 610y impacts are out of sync by .3 mils.
If I correct the velocity to match 610y impacts (at 2500fps). Then the 360y is off by .2 mils and 760y is off by .4 mils

 

[J Batt]

That combo absolutely can be 2,450-2,500fps MV. I’ve seen several lot# that were at 2,500fps or just below from 20” barrels.

Even while correcting the velocity to 700y impacts, the curve of the trajectory is not lining up with the calculator.
For now I will correct the velocity to 700y impacts, but impacts at closer ranges will be high compared to what the calculator is producing.

 

[J Batt]

At 360y a muzzle velocity of 2600fps is correct for impacts.
But at 610y a muzzle velocity of 2500fps is correct for impacts.
And at 760y a muzzle velocity of 2440fps is correct for impacts.
This is the problem. If I choose a velocity for one yard line then all the others are wrong. It’s behaving as if the BC is changing down range.

 

[Macintosh]

Well, the bc IS changing downrange because bc is a function of velocity, ie it changes during the course of the trajectory. But that isnt the problem, its not enough to create a discrepancy like that at the ranges you are talking about.

For what its worth you are just a couple tenths different than my 24” tikka at 2660fps and its tracking fairly linearly with mine, which is velocity trued but using the AB custom drag curve. (Hornady 140gr bthp)

How many shots at each distance? Are you just seeing a few impacts landing at different areas within your actual cone of fire, rather than differences in required elevation at each distance?

 

[J Batt]

Well, the bc IS changing downrange because bc is a function of velocity, ie it changes during the course of the trajectory. But that isnt the problem, its not enough to create a discrepancy like that at the ranges you are talking about.

For what its worth you are just a couple tenths different than my 24” tikka at 2660fps and its tracking fairly linearly with mine, which is velocity trued but using the AB custom drag curve. (Hornady 140gr bthp)

How many shots at each distance? Are you just seeing a few impacts landing at different areas within your actual cone of fire, rather than differences in required elevation at each distance?

Im using three shot groups before making corrections. Once I’m in the ballpark I send about 10 shots to verify. Its tracking around 1.5moa at all yardlines, and the impacts follow my corrections easily.

 

[LongWayAround]

At 360y a muzzle velocity of 2600fps is correct for impacts.
But at 610y a muzzle velocity of 2500fps is correct for impacts.
And at 760y a muzzle velocity of 2440fps is correct for impacts.
This is the problem. If I choose a velocity for one yard line then all the others are wrong. It’s behaving as if the BC is changing down range.

The problem is you are guessing and making assumptions.

Borrow or buy a chronograph before you get all twisted up.

You probably have compounding errors somewhere along the way.

I can't help but wonder about your sight height.

What are you shooting at extended range? Have you tried shooting for a waterline at that 600ish?

 

[Macintosh]

My 140 eldm dope is not what I would call “finished”, but its really close to yours. Makes me think your calculator is not crazy.
Using 2595fps chrono velocity, .295g7 bc, 100 yard zero, DA of 1850’, this is from a 20” tikka barrel.

The chart is set for every 50 yards to show, but to compare to your distances:
1.9@360
4.5@610
6.4@760

Is it correct that your 760yd dope is from a different altitude from the others? Also a different day?

 

[112Savage]

My guess would be in order of impact.
Sight height
Velocity
BC truing
Stability

 

[J Batt]

My 140 eldm dope is not what I would call “finished”, but its really close to yours. Makes me think your calculator is not crazy.
Using 2595fps, .295g7 bc, 100 yard zero, DA of 1850’, this is from a 20” tikka barrel.

The chart is set for every 50 yards to show, but to compare to your distances:
1.9@360
4.5@610
6.4@760

Is it correct that your 760yd dope is from a different altitude from the others? Also a different day?

View attachment 914994

Thanks a bunch for this. I did shoot 760y at a different location.
I’ve never had an issue using the Ballistic AE app before on about half a dozen other rifles. It’s always lined up beautifully once I true the velocity to my impacts.

My guess would be in order of impact.
Sight height
Velocity
BC truing
Stability

Thanks. My sight height is 1.75. The app rounds up to 1.8. I’ll try going over everything again. For now I’ll use the lower velocity established at 760y.

 

[Kyguy]

Get a chrono..... lots of Hornady ammo runs slow. I've got two boxes of American Whitetail 140gr .270 that's supposed to be 2940 out of 24" barrel and it ran 2700 out of two different rifles with 24" barrels. Back when I playing with a 6.5 Grendel, EVERY single box of Hornady, even different lots and loads, was a couple hundred fps slower than the box velocity, even with 20", 24" and a 26" barrels. It was oddly consistent across the barrel lengths, only about 75fps difference between the 20" and 26", but 200-300fps slow overall.

 

[ztc92]

My 20” Tikka CTR was almost exactly 2600 FPS with factory 140 ELDM loads. As others had said, if your barrel is on the slow side it could be closer to 2500.

How many rounds on the barrel so far?

 

[eric1115]

I'll echo the folks saying to get a chrono. 2450 is definitely possible. Also, what was wind doing when you were shooting?

Head wind or tail wind if you are shooting up or down a hill can make elevation do funky things. 0.3 at 500ish isn't uncommon where I often shoot, if there's a moderate tailwind. Most of the target locations are ~10° up and that wind flows with the terrain.

I'd be very surprised if it's a tracking issue, but kill two birds with one stone and shoot a 10 round zero recheck, then dial 5 mils and shoot another 10 round group and measure center to center.

Were you supported the same way for all your groups? I've seen guys pull a rear bag for a further target to get more elevation and end up shooting high because they are not supporting the back of the gun under recoil the same way as they were before.

We're your groups at distance decent size (number of shots and group size)? Some guys shoot one to three rounds on a steel plate at distance and call it dope. You could be anywhere in a .5 mil spread pretty easily doing that.