Hornady 4dof vd BCs

[RPR300WM]

So when I run Hornady 4dof vs using a single G7 BC in a standard solver, I have to use a G7 BC of .410 to achieve comparable results (within a .1-.2 MOA) vs 4dof for a 225gr eld at 2880fps.

Somehow I can't believe the 4dof could be right if I need a .410 BC to provide equivalent elevation dope out to 1500 yards. I confirmed all inputs were equivalent so what gives ?

 

[Long Range 338]

Two different calculations.... 4DOF is using doppler radar measurements for each bullet that is in their database. The BC calculator is a standard 3DOF calculator and Hornady hasn't invested any time/effort into putting their own polishes on it, it appears very basic.

 

[RPR300WM]

Two different calculations.... 4DOF is using doppler radar measurements for each bullet that is in their database. The BC calculator is a standard 3DOF calculator and Hornady hasn't invested any time/effort into putting their own polishes on it, it appears very basic.

I haven't seen anyone whos actually shot out to 1200+ yards with this bullet come up with a g7 BC that was much higher than .370 when correlating to their actual dope. Seems like the 4dof is optimistic for this bullet

 

[Long Range 338]

Are you matching the 4DOF and BC version to your real world results or just comparing before actual shooting? Hornady's published BC should be in the ballpark. In my experience the 4DOF numbers are quite good. You may have to true you data with the axial form factor to reproduce your real world results but it works well. Other than that its just a matter of verifying your inputs and making sure you have the same data entered into both versions.

 

[RPR300WM]

Are you matching the 4DOF and BC version to your real world results or just comparing before actual shooting? Hornady's published BC should be in the ballpark. In my experience the 4DOF numbers are quite good. You may have to true you data with the axial form factor to reproduce your real world results but it works well. Other than that its just a matter of verifying your inputs and making sure you have the same data entered into both versions.

I'm comparing them before I've shot beyond 440 yards , however, when others have trued the g7 BC to their actual results at long range it's no where near as optimistic as the 4dof result (equivalent to .410 bc from what I can tell) based upon what theyve reported.

In other words, you'd really have to do a lot of truing on the 4dof to make it match their actual trajectory. Not so much if you just use hornadys bc by mach # info.

 

[Long Range 338]

We would have to review all the inputs to see what is actually going on. Do you have the actual dope to compare against? It's possible Hornady has an error in their system but without all the data that is being input to analyze its just shooting into the dark.

 

[Ledzep]

I'm headed out today to shoot some 225's out to 1600+. Possibly sling a few at 1900 but it's 20mph wind so no promises. I should for sure get good data to 1200. I'll keep a long of enviro data and actual dope required and if I remember will come back here and compare.

 

[Ledzep]

225 ELD-M
2910 FPS (Lab Radar)
2.56" sight over bore
POI is 0.9" low at 100yd-- I use zero angle in 4 DOF so I don't really worry about having an exact 100yd zero so if you use a 100yd zero, figure a .25 mil offset accordingly
Zero angle: 0.6867
1:9 twist barrel
1.08 Axial form factor (everything in this barrel has been 1.06-1.08)

Enviro data is on the screen shots.

This was 4DOF today and it was spot on for elevation out to the 1925yd target. Prior to the screenshots below I walked out 100, 600, 800, and center punched everything (IPSC torsos). I was 2/3 at 1200 (18" disk I think), 2/5 at 1637yd on a IPSC torso, and 3/10 at 1925 on a 24x24" square. Misses were all wind except for 1 high shot at 1637-- it varied from 13mph to 24mph and was fairly gusty, hard to be repeatable past 1000.


Just remember, you need to subtract like 0.25 mils from all of these to get a 100yd zero equivalent.

 

[Ledzep]

Using the Hornady G7 side this is what I need to get similar outputs (accounting for my .25 mil zero offset):

1202: G7 BC of .400

1637: G7 BC of .402

1925: G7 BC of .398-.399

 

[RPR300WM]

Using the Hornady G7 side this is what I need to get similar outputs (accounting for my .25 mil zero offset):

1202: G7 BC of .400

1637: G7 BC of .402

1925: G7 BC of .398-.399

Interesting. While I haven't shot beyond 440yards yet to really tell the difference. The 4dof results for my particulars (2880fps, 2.65" scope height, 28.82" Hg, 70F, 1:9 rifling) requires. G7 of .410 BC to provide similar trajectory to the 4dof with a 1.0 axial form factor . The fact that your form factor is 1.08 means that the 4dof was optimistic for elevation and required a pretty good tweek to have it match your actual.

Btw. Hornady gives two sets of BCs for this bullet. One set for 1:10. The other for 1:7. Like you, I have a 1:9 so I wonder if it's appropriate to linearly interpolate between the two sets of BCs for something in between.

Thanks for the data!

 

[Long Range 338]

Interesting. While I haven't shot beyond 440yards yet to really tell the difference. The 4dof results for my particulars (2880fps, 2.65" scope height, 28.82" Hg, 70F, 1:9 rifling) requires. G7 of .410 BC to provide similar trajectory to the 4dof with a 1.0 axial form factor . The fact that your form factor is 1.08 means that the 4dof was optimistic for elevation and required a pretty good tweek to have it match your actual.

Btw. Hornady gives two sets of BCs for this bullet. One set for 1:10. The other for 1:7. Like you, I have a 1:9 so I wonder if it's appropriate to linearly interpolate between the two sets of BCs for something in between.

Thanks for the data!

The BCs given by Hornady are a starting point, this is the whole purpose of axial form factor (truing). If you are not getting good data at 400 yards there is something wrong...

 

[RPR300WM]

The BCs given by Hornady are a starting point, this is the whole purpose of axial form factor (truing). If you are not getting good data at 400 yards there is something wrong...

My data at 440 is fine as there's little difference between the two calculators at such short range.

I was just noticing the discrepancy between the two calculators at longer ranges. Interestingly, when I plug in an axial form factor of 1.08 suddenly the results between the 4dof and the traditional G7 model using BCs interpolated between the sets of BCs @1:10 & 1:7 yields an overall elevation difference within .25 MOA out to 1500yards. This tells me that using the interpolated G7 values from Hornady would likely be much closer to actual than the 4dof with a 1.0 axial form factor as a starting point.

 

[Ledzep]

Hard to say whether or not it's "overstated". The data in the file is pulled from live fire recordings on radar so it's very hard to fudge to make it look better-- and defeats the purpose of doing the testing if it doesn't line up. IIRC they shoot several barrels with/without brakes, cans, etc.. to try to get a good average location for 1.0. Another thing to consider is that the Hornady G1/G7 BC's are derived from the same doppler velocity data that the 4dof bullet files are made from.

The trend seems to be that muzzle brakes and especially suppressors cause the form factor to go up. This is my only precision .30 cal barrel that I can shoot 225's in so it's the only example I have-- but like I said above, this barrel produces 1.06-1.08 FF with ALL the bullets I've shot in it. I have had several 6.5mm barrels and have had them be anywhere from 0.95-1.07 with 140, 143, and 147's.

This .300 PRC is a 31" gain-twist barrel with a 9" can on the end-- it wouldn't surprise me at all if gain twist, the can, and long barrel all combine to cause more drag in flight....

Anyway, doesn't seem to be an issue-- I set my zero angle, corrected form factor once at 800, and have been fine from 100 to 2000 ever since. Looking to stretch past 2000 here in the next month or two hopefully.

 

[RPR300WM]

Hard to say whether or not it's "overstated". The data in the file is pulled from live fire recordings on radar so it's very hard to fudge to make it look better-- and defeats the purpose of doing the testing if it doesn't line up. IIRC they shoot several barrels with/without brakes, cans, etc.. to try to get a good average location for 1.0. Another thing to consider is that the Hornady G1/G7 BC's are derived from the same doppler velocity data that the 4dof bullet files are made from.

The trend seems to be that muzzle brakes and especially suppressors cause the form factor to go up. This is my only precision .30 cal barrel that I can shoot 225's in so it's the only example I have-- but like I said above, this barrel produces 1.06-1.08 FF with ALL the bullets I've shot in it. I have had several 6.5mm barrels and have had them be anywhere from 0.95-1.07 with 140, 143, and 147's.

This .300 PRC is a 31" gain-twist barrel with a 9" can on the end-- it wouldn't surprise me at all if gain twist, the can, and long barrel all combine to cause more drag in flight....

Anyway, doesn't seem to be an issue-- I set my zero angle, corrected form factor once at 800, and have been fine from 100 to 2000 ever since. Looking to stretch past 2000 here in the next month or two hopefully.

All im saying is that you would have required a much smaller amount of "truing" using hornadys 1;10 G7 BCs (3 according to mach #) vs the 4dof if you needed a 1.08 form factor to make it work. Having said that, im glad your dialed in and enjoy pushing it our further !

Thanks again for the info; it was very informative.

 

[b6graham]

Interesting. While I haven't shot beyond 440yards yet to really tell the difference. The 4dof results for my particulars (2880fps, 2.65" scope height, 28.82" Hg, 70F, 1:9 rifling) requires. G7 of .410 BC to provide similar trajectory to the 4dof with a 1.0 axial form factor . The fact that your form factor is 1.08 means that the 4dof was optimistic for elevation and required a pretty good tweek to have it match your actual.

Btw. Hornady gives two sets of BCs for this bullet. One set for 1:10. The other for 1:7. Like you, I have a 1:9 so I wonder if it's appropriate to linearly interpolate between the two sets of BCs for something in between.

Thanks for the data!

this is what stood out to me. very minor error potential, but seems a little off.