- Thread starter jugi16
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Yes, there is. There are two main models in the 4DOF app, the 4DOF custom curves measured by Hornady and a standard BC input. Set your profile up as a BC profile and have at it.
ETA: If you’re picking a bullet from a list, you’ve already gone too far, you’re in the custom 4DOF curve model.
Why wouldn’t you want to use the 4DOF data if it’s available?
Because, insofar as I've been able to ascertain in a few hours of experimentation, the 4DOF-supplied .22LR drag curves don't come close to matching observed data.
Yeah yeah I know... garbage in garbage out. I use an indoor range - level, precise range measurement, zero crosswind - to set my zero, and I use a caliper to measure impact distances from POA - Hornady emphasizes the necessity of getting these right. But here's the thing that I'm still waiting to hear from Hornady about: why do they get different drag curves for Lapua Center-X, Lapua Midas+, and SK Standard+ at a given velocity when all three use the same bullet?
Because of the way 4DOF works, truing of their supplied curves to match observed data is extremely limited (via axial form factor). I've watched the Hornady podcasts that get fairly deep into setting up the app, and their contention is that correct inputs will yield correct outputs and truing isn't needed.
Well, I am slowly gaining confidence in the app with centerfire bullets in their library, but I have absolutely no confidence at all in their supplied .22LR curves. I only know one other person who uses 4DOF for .22LR, and he doesn't use their curves either.
The only way I've been able to make 4DOF match observed data with .22LR is via the BC calculator.
Yeah... .22lr can be a sticking point with 4DoF. Unfortunately the way lead projectiles (no jacket) work in 22lr, the bore shapes the projectile and you get much greater variance barrel-to-barrel than what we see with jacketed stuff.
We narrowed the window for axial form factor to +/- 10% because 98 times out of 100 with jacketed bullets if you have to adjust more than 6% off of the file, you probably have something else jacked up (MV, sight over bore, scope issues, etc.). Drastically swinging the drag curve in most situations is the wrong thing to do...
However... It seems like in the .22 rimfire world lot-to-lot variations and especially barrel-to-barrel variations on deformation/shaping of the bullet cause wider swaths of drag curve shape. It's come up a few times now and we've discussed it internally but we probably need to do some more in-depth testing to get a better handle on it.
We narrowed the window for axial form factor to +/- 10% because 98 times out of 100 with jacketed bullets if you have to adjust more than 6% off of the file, you probably have something else jacked up (MV, sight over bore, scope issues, etc.). Drastically swinging the drag curve in most situations is the wrong thing to do...
However... It seems like in the .22 rimfire world lot-to-lot variations and especially barrel-to-barrel variations on deformation/shaping of the bullet cause wider swaths of drag curve shape. It's come up a few times now and we've discussed it internally but we probably need to do some more in-depth testing to get a better handle on it.
Thanks. I just picked up a 4DOF Kestrel to try. Mainly for rimfire. I see now that was not a good idea.
Would it be feasible to create a standalone 4DoF calculator for .22LR alongside the existing centerfire 4DoF and BC solvers? Given the vagaries of .22LR calculations for the reasons you mentioned and the attention .22LR gets trying to set up accurate solutions, I think Hornady would create a monster hit by applying its expertise and resources to .22.
Fwiw, I used a Lapua-supplied drag curve with the now-technically-banned Strelok Pro, which also provided RA4 and other curves for .22LR... and the Lapua drag curve worked best of them all. Yes, I had to true for every brand/label/lot that I used for extended range (150-400 yards), but I could pretty much rely on the solutions.
The problem isn't really with the existing calculator as I understand it. It's more the crimped lead bullets and how they're currently modeled. The act of firing the cartridge changes the shape of the bullet. 4DoF uses two main pieces, one is the drag data acquired by live fire on the doppler, the other is largely from a physical model of the bullet. If the bullets are changing shape when fired it causes weirdness for the calculator vs. real-world because of the difference in real world projectile vs. modeled projectile.
To be honest with you I'd need to talk with a few people to refresh what the real limitations of the problem are. I don't shoot .22lr for precision/LR so I'm not as familiar with it as I'd like to be. I think it's just something that will take more work on our end to get a better model the bullets in their fired state for the data that gets pulled, as well as acquiring a variety of barrels, twists, and rifling types to test the bullets out of. I'm pretty confident something we're capable of doing, and I think something we should/will do, it's just a matter of time and (diverting) resources. I believe it's on several peoples' radar, just in a race with everything else for the schedule.
I’m not sure on this one; I use 4DOF and it’s been great to 200 once trued. Not much mileage past that though, so if it can’t hold up at 3-400 I wouldn’t be in a position to know
