Ballistic Data question
- Thread starter VegaSSG32
- Start date
http://www.snipercentral.com/308-match-ammo-comparison-168gr/#table
You may find what your looking for here.
You may find what your looking for here.
You know the velocity. You know the bullet BC. That's all you need for ballistic tables. There are free calculators at several places on line. The most comprehensive are at the JBM ballistics site.
You can increase accuracy a little further using Bryan Litz's measured BC's for the Sierra bullet. Select the G7 ballistic coefficient type in the JBM calculator and use Litz's 0.218 value for this bullet (G7 values are lower than the usual G1 values, but that's because the G7 function models lower drag in the first place and needs a smaller value to give correct results). The most accurate calculation possible will be to use the BRL measured entire drag function for this particular bullet done for M852 ammunition years ago. The QuickTARGET Unlimited software that comes with QuickLOAD has this model in its database. But realistically, the difference will be smaller than the sight adjustments you can make in most instances.
Keep in mind that the 168 suffers a dynamic stability problem below about 1400 fps, and unless you want to risk keyholing, you don't want to shoot it further than it takes to drop to that velocity (about 700 yards at that MV). As a practical matter, I stop at 600 yards with this bullet and switch to the Sierra 175 grain SMK or their 155 grain Palma bullet for greater range.
The only other information you may lack is that the velocity will be for a SAAMI standard 24" barrel unless it was tested in a CIP barrel, in which case it will most likely be 600mm or 23.6". The standard velocity is measured at 15 feet or about 5m from the muzzle, so figure the equivalent of 11 fps faster for velocity right at the muzzle (though that is only an equivalent for an ideal gun that produces no muzzle blast; actual dynamics and velocities around a muzzle are more complicated than that).
You can increase accuracy a little further using Bryan Litz's measured BC's for the Sierra bullet. Select the G7 ballistic coefficient type in the JBM calculator and use Litz's 0.218 value for this bullet (G7 values are lower than the usual G1 values, but that's because the G7 function models lower drag in the first place and needs a smaller value to give correct results). The most accurate calculation possible will be to use the BRL measured entire drag function for this particular bullet done for M852 ammunition years ago. The QuickTARGET Unlimited software that comes with QuickLOAD has this model in its database. But realistically, the difference will be smaller than the sight adjustments you can make in most instances.
Keep in mind that the 168 suffers a dynamic stability problem below about 1400 fps, and unless you want to risk keyholing, you don't want to shoot it further than it takes to drop to that velocity (about 700 yards at that MV). As a practical matter, I stop at 600 yards with this bullet and switch to the Sierra 175 grain SMK or their 155 grain Palma bullet for greater range.
The only other information you may lack is that the velocity will be for a SAAMI standard 24" barrel unless it was tested in a CIP barrel, in which case it will most likely be 600mm or 23.6". The standard velocity is measured at 15 feet or about 5m from the muzzle, so figure the equivalent of 11 fps faster for velocity right at the muzzle (though that is only an equivalent for an ideal gun that produces no muzzle blast; actual dynamics and velocities around a muzzle are more complicated than that).
jwrowland77
New member
I haven't been that happy with using G7. When I use the G1 data, and other data like MV, plug those into my Ballistic AE app, I always get closer results using G1.
http://www.norma-usa.com/index.php/ballistics
Check the load list to the left. I like this program for the fast acting sliders below the graph. Enjoy!
Check the load list to the left. I like this program for the fast acting sliders below the graph. Enjoy!
Jwrowland77 said:
It would depend what bullet shape you use. If it is a round nose or resembles the one in Jules Verne's, From the Earth to the Moon (below), then, yes, a correctly selected G1 coefficient will do better. But if it's a modern boattail with Spitzer nose, then a correctly selected G5 or the G7 BC will do better because it will have a more closely matching drag vs. Mach number curve. In that instance, a G1 won't track as well unless the G7 is incorrect for the actual conditions.
(Public domain image)
jwrowland77
New member
These were match bullets. Hornady and SMK. Tried both ways on both of them. Found for my rifle and load G1 gave me closer results.
Thanks guys for the replies. All useful info
I guess I should have been a bit more specific. I have ballistic data for this round off of my ballistic software and field shooting. I was just wondering what the factory ballistic were. Because you cannot find this ammo on NORMA-USA or on they're ballistic software. It is a Sierria matchking HPBT.
Even at 168gn. In my rifle, it doesn't go trans-sonic till around after the 800yard line. Then starts to loose a little stability. But really not bad at a grand. I just can't believe I cannot find this ammo or any ballistic data any where on NORMAs website.
I guess I should have been a bit more specific. I have ballistic data for this round off of my ballistic software and field shooting. I was just wondering what the factory ballistic were. Because you cannot find this ammo on NORMA-USA or on they're ballistic software. It is a Sierria matchking HPBT.
Even at 168gn. In my rifle, it doesn't go trans-sonic till around after the 800yard line. Then starts to loose a little stability. But really not bad at a grand. I just can't believe I cannot find this ammo or any ballistic data any where on NORMAs website.
JW,
That actually shouldn't be physically possible, but all the condition ducks do have to be in a row. For example, if the temperature was a little cooler over the range than was used in the calculator argument, the speed of sound calculation would be high and that could make the G1 curve look like a better predictor of elevation at certain ranges. The same could happen if your chronograph reads a bit high. My dad has an old one that adds about 200 fps at .308 Win velocities and that would cause a similar appearance. A side wind from the left (for a right hand twist barrel) could make the bullet drop further than a G7 BC predicts. A scoped sight might not have its MOA detents exactly correct. All that stuff could do it. But unless the laws of physics have changed, something is not what it appears to be.
I can give you an example from target shooting. Any time I use a ballistics program to provide come-ups for an iron sight match, they always want me to put too much elevation on when I move from 300 yards to the 600 yard line. That's regardless of the BC model used. The cause isn't the ballistics software or the drag functions, but rather is how much my vision blurs the target when I focus on the front sight. It makes where I locate the 6:00 hold shift up over what I see at 300 yards. Just my personal quirk of coordination and perception. All I can do is be aware of it and compensate.
Vega,
What number is not on your list in the OP that you need?
That actually shouldn't be physically possible, but all the condition ducks do have to be in a row. For example, if the temperature was a little cooler over the range than was used in the calculator argument, the speed of sound calculation would be high and that could make the G1 curve look like a better predictor of elevation at certain ranges. The same could happen if your chronograph reads a bit high. My dad has an old one that adds about 200 fps at .308 Win velocities and that would cause a similar appearance. A side wind from the left (for a right hand twist barrel) could make the bullet drop further than a G7 BC predicts. A scoped sight might not have its MOA detents exactly correct. All that stuff could do it. But unless the laws of physics have changed, something is not what it appears to be.
I can give you an example from target shooting. Any time I use a ballistics program to provide come-ups for an iron sight match, they always want me to put too much elevation on when I move from 300 yards to the 600 yard line. That's regardless of the BC model used. The cause isn't the ballistics software or the drag functions, but rather is how much my vision blurs the target when I focus on the front sight. It makes where I locate the 6:00 hold shift up over what I see at 300 yards. Just my personal quirk of coordination and perception. All I can do is be aware of it and compensate.
Vega,
What number is not on your list in the OP that you need?
jwrowland77
New member
Yeah, I found it weird as well. Tested it several times over about a year span. Inputting weather conditions etc etc.....
jwrowland77
New member
Yes. Trans is when the sound barrier catches back up with the bullet. Thats why the 168's don't do good. Something about the angle of the boattail. When that wave catches back up, the angle on the 168's don't transition well.
jwrowland77
New member
JW,
Do you still have the data? I'd be interested to run it against the BRL's drag function for that bullet.
Vega,
OP is either the "Original Post" that started the thread, or the Original Poster who started the thread, depending on the context.
Specifically, the data you listed in the original post are the factory muzzle ballistics. That's what Midway and other sellers put up in their product descriptions. Since you have that, and since all the ballistic performance, range tables, and so on, can all be calculated from those numbers using one of the software packages mentioned, I'm not clear what else you are asking for?
Trans is short for transonic, the bullet speed transition from supersonic to subsonic (and in both directions for aircraft). Its significance is that there is a big jump increase in drag coefficient in that range, peaking right at the speed of sound itself. The overall sudden increase in drag as you speed up toward the speed of sound is what used to be more commonly called "the sound barrier" when aircraft were being developed to break through it. It refers to the huge extra engine thrust you need to get past that velocity limit and continuing up even faster. It's caused by the extra work load of compressing air out in front of the craft into shock waves.
It's interesting that you can get some long range out of those bullets. When I first ran into the problem was at Gunsite in a Precision Rifle class when nobody in our class could hit a 748 yard popper using ammo loaded with them except by accident. They zipped left and right. We shrugged it off, putting it to the 20 mph crosswind we had over the valley between our firing point and the popper. Then a year later I was at Mid Tompkins Long Range Firing School at Camp Perry and the first shooting was at 800 yard LR targets. Everyone shooting .30 cal medium power cartridges had brought the 168's and nobody in the class could stay on paper, much less get a zero, and the pits called back to say they were seeing keyholes where bullets did hit the targets. That year, then Sierra Ballistic tech Kevin Thomas was shooting in the class (.300 WM with heavier bullets) and he told us the 168 had originally been designed for 300 meter International Rifle, that the company lucked out when it did well to 600 yards, but that it was never meant for long range. He recommended switching to the 175 which was intended for long range.
So, at the lunch break we all ran off to Commercial Row and bought ammo loaded with the 175. There was both Federal and HSM available. After lunch for the second range session, there were no more keyholes. IIRC, I posted a 99 on my first target.
A number of years later, Bryan Litz came out with his first book, Applied Ballistics for Long Range Shooting, and in it mentioned the dynamic stability problem for the 13° boattail bullet. The 175 uses the old 9° boattail developed empirically by the military just after WWI.
Do you still have the data? I'd be interested to run it against the BRL's drag function for that bullet.
Vega,
OP is either the "Original Post" that started the thread, or the Original Poster who started the thread, depending on the context.
Specifically, the data you listed in the original post are the factory muzzle ballistics. That's what Midway and other sellers put up in their product descriptions. Since you have that, and since all the ballistic performance, range tables, and so on, can all be calculated from those numbers using one of the software packages mentioned, I'm not clear what else you are asking for?
Trans is short for transonic, the bullet speed transition from supersonic to subsonic (and in both directions for aircraft). Its significance is that there is a big jump increase in drag coefficient in that range, peaking right at the speed of sound itself. The overall sudden increase in drag as you speed up toward the speed of sound is what used to be more commonly called "the sound barrier" when aircraft were being developed to break through it. It refers to the huge extra engine thrust you need to get past that velocity limit and continuing up even faster. It's caused by the extra work load of compressing air out in front of the craft into shock waves.
It's interesting that you can get some long range out of those bullets. When I first ran into the problem was at Gunsite in a Precision Rifle class when nobody in our class could hit a 748 yard popper using ammo loaded with them except by accident. They zipped left and right. We shrugged it off, putting it to the 20 mph crosswind we had over the valley between our firing point and the popper. Then a year later I was at Mid Tompkins Long Range Firing School at Camp Perry and the first shooting was at 800 yard LR targets. Everyone shooting .30 cal medium power cartridges had brought the 168's and nobody in the class could stay on paper, much less get a zero, and the pits called back to say they were seeing keyholes where bullets did hit the targets. That year, then Sierra Ballistic tech Kevin Thomas was shooting in the class (.300 WM with heavier bullets) and he told us the 168 had originally been designed for 300 meter International Rifle, that the company lucked out when it did well to 600 yards, but that it was never meant for long range. He recommended switching to the 175 which was intended for long range.
So, at the lunch break we all ran off to Commercial Row and bought ammo loaded with the 175. There was both Federal and HSM available. After lunch for the second range session, there were no more keyholes. IIRC, I posted a 99 on my first target.
A number of years later, Bryan Litz came out with his first book, Applied Ballistics for Long Range Shooting, and in it mentioned the dynamic stability problem for the 13° boattail bullet. The 175 uses the old 9° boattail developed empirically by the military just after WWI.
Unclenick,
You are right. 175gn is the way to go when looking for decent shot groups at that range. When I said ok out to a grand. I meant we could hit the target. 4'x32" steel silloette but on paper not getting better than 12"-15"-18" shot groups. And you can see key holes with the 168gn on paper targets looks like at 825 but definitely at 850. That's why I am Curious if anyone knew the ballistic data for this round. I can't even find this round on NORMAs website. Or NORMAs ballistic app. Is the muzzle velocity really 2720??? Or is actually slower than advertised...
You are right. 175gn is the way to go when looking for decent shot groups at that range. When I said ok out to a grand. I meant we could hit the target. 4'x32" steel silloette but on paper not getting better than 12"-15"-18" shot groups. And you can see key holes with the 168gn on paper targets looks like at 825 but definitely at 850. That's why I am Curious if anyone knew the ballistic data for this round. I can't even find this round on NORMAs website. Or NORMAs ballistic app. Is the muzzle velocity really 2720??? Or is actually slower than advertised...