6.5 Creed Truing, could this be right?

[Jack Master]

So I am helping a friend get his 6.5 creedmoor setup and trued. Last night we shot 600yds and 1000yds to true his Hornady ballistic program.
Here is the field data.

Rifle - Savage FV in an MDT chassis with Athlon Midas Tac. (not mine, so don't complain about it)
Ammunition - handloads, Hornady 129sst, Hornady Brass, Primer??, H3450 (not sure of grains), MV = 2725ish
Weather - 50deg, 29.25 Station pressure, 60% hum
600yd drop = 4.2mils (4" group)
1000 yd drop = 12.1mils (8" group... I was impressed with this bullet)
Wind - 4:30 @ 7mph

The factory G1 BC from Hornady is 0.485. We are using the G1 because Hornady does not offer a G7 or a custom drag model for this bullet. To get the program to true out we worked all the way down to a G1 BC of 0.35 and a MV of 2880. IS this okay to drop the BC this far and increase MV that far?

Data ----Factory---------Trued
MV ------27.25ish--------2880
BC--------0.485-----------0.35

I checked the Applied ballistic book of bullets after getting home last night and they also said to use 0.482 for the BC. I want to go back and try truing the program with the G7 suggested by AB.
I had to repeat to myself 3 time last night "Believe the bullet" as I have pushing the BC that low. The two data points did line up and our next step will be verify this trued program at each 100yards. But, man!, that is a big change for from the measured data. Is it okay?

...... ..... "Believe the Bullet, Believe the bullet, Believe the bullet"

 

[Deleted member 113831]

It shouldn't have taken anywhere near 12.1 mils at 1k yards.

If 12mils was true drop, then either your speed wasn't 2700+fps...or the distance wasn't 1k yards...or the scope shit the bed.

My 308 doesn't even use 12mils at that distance, and it's only moving 2630fps

 

[Jack Master]

It shouldn't have taken anywhere near 12.1 mils at 1k yards.

If 12mils was true drop, then either your speed wasn't 2700+fps...or the distance wasn't 1k yards...or the scope shit the bed.

My 308 doesn't even use 12mils at that distance, and it's only moving 2630fps

Thanks. I thought the same of the 12.1 mils. When I got on the rifle it was 11.9. ( I manage recoil different) so I can say the dial was right.
We've done a scope tracking test up to 9 mils but not to 12, we'll recheck this. We'll bust out he chronograph this weekend and give tha go.

 

[morganlamprecht]

It shouldn't have taken anywhere near 12.1 mils at 1k yards.

If 12mils was true drop, then either your speed wasn't 2700+fps...or the distance wasn't 1k yards...or the scope shit the bed.

My 308 doesn't even use 12mils at that distance, and it's only moving 2630fps

this^^ something isnt right with the system or the inputs

 

[wyliecoyote]

This is a fairly similar problem that I'm also having being a new long range shooter with the 6.5 Creedmoor. My biggest question is this: why would you mess around with BCs and MVs to make your software spit out a contrived solution for a specific set of conditions? The MV, and to a greater/lesser extent the BC, are known, measured values, so why lie to the software?

I've been using a Kestrel 5700 Elite with the AB Custom Drag Model for my bullet (Hornady 143 gr ELD-X) and had great results shooting out to 1000 yds all last summer and into early fall. However, when the weather got colder and my barrel speed up around with 800-900 rds through it (from 2750ish to 2800 fps), I started getting bad elevation data from the software, even with up to date MVs for the conditions. With a custom drag curve like AB's or Hornady's 4DOF, aren't you taking BC out of the equation and using a measured doppler radar trajectory instead? Perhaps I can see playing around with BCs in the absence of a custom drag curve, but with such a curve, there shouldn't be any need to mess with the BC or MV? What good does it do to true your software by adjusting BC/MV for one set of conditions? You'd have to have a log book of every condition you'd expect to shoot in that would take years to build. The whole idea of having the Kestrel paired with such a drag curve was to account for changing conditions. Am I just expecting technology to provide short cuts to something that's an art form learned over many years?

 

[Jack Master]

I am not asking for a "contrived solution for specfic set of conditions". I am truing my program to my rifle for that day's conditions so the program will work correctly everyday with different weather conditions.

My biggest question is this: why would you mess around with BCs and MVs

I had to use the BC because Hornday does not offer a custom drag model for that bullet. The only other option is use a BC. This forces us to change the MV and BC to match our field data (600yd = 4.2 and 1000yds = 12.1). It is very unlikely I can simply put in my MV and BC and everything lines up perfectly to what my rifle system needs. Rather, we need to true our ballistic program to match what our rifle is doing. The only way to do that is by changing the MV and the BC in one way or another, especially when a custom drag model is not available.

make your software spit out a contrived solution for a specific set of conditions?

The "specific set of conditions" was the weather the day we were doing the shooting. If we are using an app on a phone we need to document that weather to put it in our data program when truing it. If I shoot on a cold day (30deg) and true the program to my observed drop but leave the temp in the program set to 70 degrees, my program will be wrong on a an actual 70 deg day. I need to set the program to the shooting conditions of the day we gathered the drop data, this way when it becomes 70 degrees I can change my temp in the program and get the correct shooting solution. When I true the ballistic program, the weather is also input true for that day. afterward, I can change the weather conditions day to day and have an accurate program.
If you are using your kestrel its likely doing this for you already. (I don't own one) It had "logged" the current conditions when you are truing and then it changes the environment for you the next time you are out shooting. (this is the purpose of putting the ballistic program in a weather meter)

With a custom drag curve like AB's or Hornady's 4DOF, aren't you taking BC out of the equation and using a measured doppler radar trajectory instead?

Yes, this is true. But AB and Hornady still give you ways to alter that custom drag curve to match what your rifle is doing. In the kestrel AB is when you are using thier truing menu and in the Hornady is when you are changing the "Form Factor" Both of these are a similar idea of changing the BC to match your rifle or system's performance
And again, there isn't a drag curve available for this bullet.

What good does it do to true your software by adjusting BC/MV for one set of conditions?

Because its the conditions of the day we shot and collected data.

You'd have to have a log book of every condition you'd expect to shoot in that would take years to build.

Not true. I true the program for the day we collected data, this way, when I changed the environment tomorrow or next week the program will give me a shooting solution for that day's conditions.

Am I just expecting technology to provide short cuts to something that's an art form learned over many years?

Yes... that's exactly we are all expecting it to do.

However, when the weather got colder and my barrel speed up around with 800-900 rds through it (from 2750ish to 2800 fps), I started getting bad elevation data from the software, even with up to date MVs for the conditions.

Have you thought about why your kestrel was giving bad data in the winter? My guess is because you didn't true it, or you trued to the wrong weather conditions. The fellas that I have seen efficiently run a kestrel have spot-on data for deep winter, spring, fall and hot summer. You have to tell the kestrel what your rifle does to get this to work.

In summary
I think you need to seriously study what a ballistic program can do and cannot do. You also need to understand what your ballistic computer is doing with each of the inputs your are giving it including "Capturing the Environment" on the kestrel. How did the change in pressure, temp and humidity effect you ballistic program and understand how it effects your bullet. Then understand what truing it and how other programs might need to do it, not just a kestrel.

 

[Jack Master]

This is a fairly similar problem that I'm also having being a new long range shooter with the 6.5 Creedmoor. My biggest question is this: why would you mess around with BCs and MVs to make your software spit out a contrived solution for a specific set of conditions? The MV, and to a greater/lesser extent the BC, are known, measured values, so why lie to the software?

I've been using a Kestrel 5700 Elite with the AB Custom Drag Model for my bullet (Hornady 143 gr ELD-X) and had great results shooting out to 1000 yds all last summer and into early fall. However, when the weather got colder and my barrel speed up around with 800-900 rds through it (from 2750ish to 2800 fps), I started getting bad elevation data from the software, even with up to date MVs for the conditions. With a custom drag curve like AB's or Hornady's 4DOF, aren't you taking BC out of the equation and using a measured doppler radar trajectory instead? Perhaps I can see playing around with BCs in the absence of a custom drag curve, but with such a curve, there shouldn't be any need to mess with the BC or MV? What good does it do to true your software by adjusting BC/MV for one set of conditions? You'd have to have a log book of every condition you'd expect to shoot in that would take years to build. The whole idea of having the Kestrel paired with such a drag curve was to account for changing conditions. Am I just expecting technology to provide short cuts to something that's an art form learned over many years?

 

[seansmd]

Did you figure why it was needing 12 mils at 1k, even 4.2 @600y is a lot?

 

[wyliecoyote]

Jack Master,

Awesome tear down of all my questions there, thanks for taking the time to do that. The video was quite helpful too. I'll readily admit that I haven't trued the software to the gun like you've described and that's certainly the source of my woes as the seasons changed. Using nothing more than a freshly chronographed MV paired with the custom drag model worked so well all summer that I probably got overconfident with it. So it looks like I'll have to true my MV in the Kestrel AB. So far, I've only shot inside 1000 yds and am happy practicing there so messing with the Drop Scale Factor (DSF) probably won't be a player yet (AB advises to only do this in the sub-sonic region).

I'm primarily a hunter (although I'm getting more and more addicted to this kind of shooting every time out) so having a field worthy ballistic calculator is important (can't be fiddling around on a phone), hence the Kestrel and for fast shots, a wrist bar. My goal is to have a robust ballistic computer that will compensate for whatever conditions I happen to be in, backed up by printed out data. Lots to learn!

 

[wyliecoyote]

12 mils at 1000 and 4.2 @ 600 are quite a bit for a 6.5. My last trip out January I was getting an AB computed 7.8 mils @ 1000 (actual was 7.3) and at 600 a computed of 3.5 (actual was 3.3). The AB isn't terribly far off, but I do need to tweak the MV a bit. I'm pushing the Hornady 143 gr ELD-X right around 2800 fps.

 

[Jack Master]

Did you figure why it was needing 12 mils at 1k, even 4.2 @600y is a lot?

Nah. Not yet. Gonna try shooting again this weekend if it quits raining.

 

[morganlamprecht]

This is a fairly similar problem that I'm also having being a new long range shooter with the 6.5 Creedmoor. My biggest question is this: why would you mess around with BCs and MVs to make your software spit out a contrived solution for a specific set of conditions? The MV, and to a greater/lesser extent the BC, are known, measured values, so why lie to the software?

I've been using a Kestrel 5700 Elite with the AB Custom Drag Model for my bullet (Hornady 143 gr ELD-X) and had great results shooting out to 1000 yds all last summer and into early fall. However, when the weather got colder and my barrel speed up around with 800-900 rds through it (from 2750ish to 2800 fps), I started getting bad elevation data from the software, even with up to date MVs for the conditions. With a custom drag curve like AB's or Hornady's 4DOF, aren't you taking BC out of the equation and using a measured doppler radar trajectory instead? Perhaps I can see playing around with BCs in the absence of a custom drag curve, but with such a curve, there shouldn't be any need to mess with the BC or MV? What good does it do to true your software by adjusting BC/MV for one set of conditions? You'd have to have a log book of every condition you'd expect to shoot in that would take years to build. The whole idea of having the Kestrel paired with such a drag curve was to account for changing conditions. Am I just expecting technology to provide short cuts to something that's an art form learned over many years?

Jack broke down all your questions well, but what I can add is with a proper functioning complete system (rifle, scope, chrono, app, etc...all of it), it should be really close inside 6-700 yds with no truing

Always check your zero, if possible, in the same location you’re truing...don’t assume it’s zero’d because it was done at another time, even if it hadn’t been shot, zero’s shifting due to lighting/mirage conditions/etc .1-.2 are common and that will skew your data quick

With good data, and proper range on targets (another big factor) your muzzle velocity and BC should be very close...labradar or magnetospeed, are the only 2 I have extended experience with...and need minimal truing. I think I currently have 9 barrels for my match guns, and none of the velocities are off more than 10-20 fps from my labradar...it’s usually a tweak to force it to round up or down to line up perfect

BCs are also not set in stone, they shift with twist rates, bore variables, speed, etc...good match bullets like Berger, hornady, Sierra, etc should be really close...getting further into cheaper and hunting style bullets with short range inflated BCs will usually need a lot more adjustment the further u go out

last week I trued 1 one my 6mm barrels w/ 108 Berger’s, and it was within .1 at 400 and 800 yds right off the bat

in my 6.5prc, I trued hornady 140 bthp’s and 120 nosler ballistic tip hunting bullets...both were within .1 at 400 with advertised BCs, and the 140 was within .1 at 800...the nosler however was .3-.4 low @ 800 and required the BC to be adjusted from .458 to .422...checking applied ballistics afterwards, I think they had the nosler 120 BC listed at .419 or .420 iirc...just as an example for why adjustments are needed

 

[wyliecoyote]

Thanks Morgan, good perspective on the BCs and how much you're having to tweak things. Inside 6-700, I'm only seeing 0.2-0.3 Mils difference between the AB computed and actuals, but at 1000, its 0.5 Mil (without truing MV). My set up is pretty decent (good rifle, NF scope, AB Kestrel, custom loaded ammo, etc.) with me being the weak link of course (signed up for a training course in June).

During the early hunting season last year on antelope, I had great results with just a MV and the AB drag model in the Kestrel (farthest hit was 513 yds), but in December, I had a shot on a Barbary sheep at 473 yds that I missed. It's a long story, but part of that miss was me trusting what the Kestrel spit out (backed up by JBM data for that temp/elev on my wrist bar) and dismissing the verification I had done a week earlier that showed the rifle was hitting about 6" high at 400 yds. In January, I got out to my 1000 yd range, rechecked zero, and shot lots of ammo from 200 yds out to 1000, comparing the AB Kestrel with actual impacts above/below a waterline (all were above w/ the faster MV). From what I've gathered here from you and Jack Master, I definitely know where I need to go next . . . truing MV in the software.

Sorry Jack Master for hi-jacking this thread. I'll be very interested to see what you find out about those 6.5 Creed numbers your friend had.

 

[Jack Master]

Follow up to what what we found - Back to the orilgional post.

We chronograph-ed last night.
10 shots
MV = 2741 fps avg
SD = 10
ES = 36

We went out to the target and ranged back to the shooting position. We parked a truck on the spot and ranged the windshield. 1014 Yards. This checks out.

Next time shooting we are going to tall target test the scope. I'll be back with more information.

 

[Jack Master]

So I decided to check Hornady's solver and played with JBM. (Looking to match up 600yds = 4.2 and 1000 yds = 12.1)

This is n't too far off using the chronograph speed and the standard bullet information. 600 lines right up.

This tells me 12.1 is not out of the question for 1000yd drop. @Skookum - Would you agree its feasible?

Playing with the BC to true 1000yds, then Velocity for 600, then BC for 1000, then velocity for 600 (rinse and repeat 13 times) to get this:

Final BC is 0.364 and final Velocity is 2850
This tells me the Hornady app is doing this pretty well. No reason to 2nd guess it.
I am very surprised to be getting about the same data as Hornady and the BC has to drop this low. (believe the bullet...)
Plus I am seeing this is dropping into the transonic and sub sonic range (879yds). Maybe that is what's giving me weird results too.

 

[Jack Master]

Another interesting note for this rifle. This is 39.3gr H4350 in Reformed 308 brass going 2740fps. The Hornady book says 42.8 max load will get 2700ish. We are way low on powder but are getting okay velocities. The 308 reforms have 2.5 grains less H2O capacity than a Hornady case. I understand less case volume will give higher pressures, but 39.3gr getting 2740??!! Yes we have checked with multiple scales, Yes, they were correct. Nothing with this rifle is going well.

 

[Defender3]

NVM - reading is fundamental.

 

[Steel head]

Another interesting note for this rifle. This is 39.3gr H4350 in Reformed 308 brass going 2740fps. The Hornady book says 42.8 max load will get 2700ish. We are way low on powder but are getting okay velocities. The 308 reforms have 2.5 grains less H2O capacity than a Hornady case. I understand less case volume will give higher pressures, but 39.3gr getting 2740??!! Yes we have checked with multiple scales, Yes, they were correct. Nothing with this rifle is going well.

2.5 grains less capacity matters

that and a fast barrel could totally account for your results.

 

[Deleted member 113831]

So I decided to check Hornady's solver and played with JBM. (Looking to match up 600yds = 4.2 and 1000 yds = 12.1)

This is n't too far off using the chronograph speed and the standard bullet information. 600 lines right up.
View attachment 7287650
This tells me 12.1 is not out of the question for 1000yd drop. @Skookum - Would you agree its feasible?

Playing with the BC to true 1000yds, then Velocity for 600, then BC for 1000, then velocity for 600 (rinse and repeat 13 times) to get this:
View attachment 7287673

Final BC is 0.364 and final Velocity is 2850
This tells me the Hornady app is doing this pretty well. No reason to 2nd guess it.
I am very surprised to be getting about the same data as Hornady and the BC has to drop this low. (believe the bullet...)
Plus I am seeing this is dropping into the transonic and sub sonic range (879yds). Maybe that is what's giving me weird results too.

Forgive the dumb question, but is this an 129 SST, or 129 Interlock? You used the interlock name and interlock BC of G1 .445 in your JBM sheet above, but said SST in the OP.

The speed and BC (G1 .445) for the interlock almost matches the drop you are seeing, while getting the 129 SST to match requires a 25% BC reduction.

I just can't see anyway to justify that. You would literally need to shed the polymer tip in flight to make the SST perform that badly, maybe not even then.

The 129 Interlock using your numbers needs 11.5 mils according to Strelok.

 

[Jack Master]

Forgive the dumb question, but is this an 129 SST, or 129 Interlock? You used the interlock name and interlock BC of G1 .445 in your JBM sheet above, but said SST in the OP.

The speed and BC (G1 .445) for the interlock almost matches the drop you are seeing, while getting the 129 SST to match requires a 25% BC reduction.

I just can't see anyway to justify that. You would literally need to shed the polymer tip in flight to make the SST perform that badly, maybe not even then.

The 129 Interlock using your numbers needs 11.5 mils according to Strelok.

Thanks for pointing that out. My original post is incorrect. The JBM information is correct. Below if the bullet he is using. 129 Interlock. Its more on the hunting side than the long range side.
From Hornday website -

This is still a 20% reduction.
Do you think the its possible the bullet is slowing down to a tran-sonic flight that is giving the 12.1 result and this much reduction on BC?

 

[Steel head]

Thanks for pointing that out. My original post is incorrect. The JBM information is correct. Below if the bullet he is using. 129 Interlock. Its more on the hunting side than the long range side.
From Hornday website -
View attachment 7289376
This is still a 20% reduction.
Do you think the its possible the bullet is slowing down to a tran-sonic flight that is giving the 12.1 result and this much reduction on BC?

I think it’s dropping BC and therefore speed faster as it goes down range than we’re accustomed to seeing with high BC bullets.

I noticed this recently with 7mm Berger 168 classic hunters.

The listed BC works for a shorter range and you need to start adjusting the BC at distances shorter than the target bullets I’m used to.

 

[Deleted member 113831]

Thanks for pointing that out. My original post is incorrect. The JBM information is correct. Below if the bullet he is using. 129 Interlock. Its more on the hunting side than the long range side.
From Hornday website -
View attachment 7289376
This is still a 20% reduction.
Do you think the its possible the bullet is slowing down to a tran-sonic flight that is giving the 12.1 result and this much reduction on BC?

In Strelok, you get the multi-BC option to adjust BC's as the velocity slows. So you basically get to do your own BC banding.

I typically allow for a 5% decrease in BC once the velocity drops below 1900-2000fps with boat tail bullets. This about 25% velocity loss from the muzzle velocity.

For flat base bullets like the 129 Interlock, I typically double the BC loss to 10% and start that BC once the bullet drops 20% in velocity because of course faster velocity loss also means sooner velocity loss ...so in this case I would start at 2200fps.

So I used G1 .445 BC from 2741-2200fps, and G1 .400 BC from 2200-0fps.

Doing this, I get 4.4mils at 600 yards and 12mils at 1014 yards with your combo.

This is very close to what you are seeing.

Edit: even using the original 2000fps you get 4.4mils at 600 yards and 11.9 at 1014 yards.