The Accurate Reloading Forums THE ACCURATE RELOADING.COM FORUMS Guns, Politics, Gunsmithing & Reloading Reloading Don't trust ballistic tables ...Go | New | Find | Notify | Tools | Reply | |
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Finally got out to the 200 & 300 yd. range the other day. I tried two loads: .280 Rem., 139-gr. Hornady SP, 59.5 gr. RL-22, 3000 fps. .338 Win. Mag., 200-gr. Ballistic Tip, 65.0 gr. RL-15, 2950 fps. From load development I had both shooting exactly 2.0" high at 100 yds. Here are the manufacturers' table results vs. actual results: .280 book -- +1.5"@100, 0.0@200, -7.0"@300 .280 actual -- +2.0"@100, 0.0@200, -4.0"@300 .338 book* -- +1.6"@100, 0.0@200, -7.1"@300 .338 actual -- +2.0"@100, 0.0@200, -6.5"@300 [* - averaging figures for 2900 fps and 3000 fps] Of course, during this freak snowstorm (no one else at the range, it was great) the temperatures were lower than in a bullet maker's test tunnel. Will do more testing when it's warmer to double-check these results. A classic case of "your mileage may vary." I think I also observed the advantage of neck-sorting brass. The brass in my .338 loads was sorted to cull out anything more than .0015" variation in neck thickness; those loads held just over 1 MOA (3.25" @300). The .280 loads were shot with "practice" brass -- the ones that were culled out for having too much variation. While the same batch of .280 ammo shot 1 MOA at 100 yds, the 300-yd. group opened up to about 1.5 MOA. All other case prep was the same. John | ||
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Try feeding this data into a program like PointBlank and fiddle with the sight height above the bore. See if their data is for iron sights. I agree on neck wall thickness. That's where to start. It's garbage in garbage out. | |||
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Were these your velocities or the velocity listed for the load? Obviously that would cause a difference. A second point is that the sight height is important, as noted by the first reply. Most ballistics tables are standardized for a separation of the scope and bore centerline of 1.5". Most modern rifles with the ridiculous scopes being used today are nowhere near this. The third possible reason is due to bullet damage. It doesn't take much tip damage to change the ballistic coefficient considerably for a high BC design. I saw a test in a BR article where they shot duplicate loads with new bullets and identical bullets from the same lot which had simply been shaken and handled in their original plastic box. There was a big difference. The fact is that these results are not far off. At the slight angles occuring here, drops are really pretty linear from line of sight. You can look at ballistic tables with multiple zero entries to confirm this. If you look at your second set of data, you will see that there is a 0.4" difference at 100 yards. If you adjust the 300 yard numbers by 1.2" to put them on an equivalent zero basis, the difference is only about 1/2". I think this is actually incredibly close. | |||
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quote:While I appreciate your points, most of them don't apply here. Velocities were previously chronographed over multiple range sessions. I don't care for ridiculous scopes. Just measured both and they are about as close to 1.5" as I can measure without dismounting the scopes. My Ballistic Tips are all in good shape. Not easy to damage those in the box. The Hornadies were in normal shape, i.e. slightly variable after packing and shipping from Nebraska to Missouri to Virginia. Of course since manufacturers' tables are based on computer modeling, their bullet tips are always perfect. If I moved the POI up 0.4" at 100 I'd expect 1.2" up at 300. I'd also expect 0.8" higher at 200, which didn't happen. Bottom line is that I'm glad I checked. If I trusted the tables it would be awfully easy to shoot too high on a 300-yd. pronghorn, say. | |||
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quote:Hey John, Excellent topic. It is amazing to me just how relatively close some of the ballistics programs can guesstimate trajectory. That said, a person who doesn't verify the actual trajectory of his Load, in his rifle, at the distance he intends to take shots at Game, still has a lot to learn. [ 04-03-2003, 16:18: Message edited by: Hot Core ] | |||
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I agree. It is a very good topic. Now to further bring the point home, try these tests with different bullets and see what happens with the same velocities and settings. I did this once with my 308 and found that the same load with different bullets can do amazing things. In my tests (only) I found that 150 Nosler Ballistic Tips actually "rose" further than the rest of the bullets I tried. At the same velocity, they printed almost 2" higher at 100 yards than the rest. Of course, this is in my rifle and I can't say it is the same for all. The moral is, shoot 'em to make SURE where they will hit at all distances. | |||
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I bet there is even less bullet drop out west where the pronghorn are at. It would be interesting to do the same experiment at a higher elevation and lower humidity. | |||
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John I don't want to belabor this point, but I don't understand your response. You seem to agree with what I said, but disagree with the results. You obviously adjusted your zero to 2" high at 100 yds. If you adjust the two book loads to the same zero, the results would be: 338 Book +2"@100 -5.9"@300 Actual +2"@100 -6.5"@300 280 Book +2"@100 -5.5"@300 Actual +2"@100 -4.0"@300 This is probably the closest agreement I have ever seen to book values on drop, and I have checked them for years for many rifles. Most chronographs, in fact, are not this accurate. There are any number of things that can account for differences this small, such as velocity variation, temperature, air pressure, even humidity. Bottom line is, I think these numbers are in very good agreement with the data you quote. I also agree completely with the statement that no one should hunt with a load (including factory loads) until he has actually measured its performance at long range. | |||
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quote:Art, I had them 2" high at 100 and was pretty close by your calculations, but I was also dead on at 200, which shouldn't be possible by your calculations. May have to reshoot the whole dang thing sometime ... shucks. I sure wish I could make "live fire" adjustments for altitude, temperature and weather before getting on the plane ... John John | |||
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John, I have a ballistic program from Sierra, and it's really accurate. You can change your environment variables to what your actual is and you're really close. It's Sierras infinity program. It's worth it to check it out. | |||
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