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9/23/2020 3:47:02 PM
Posted: 3/9/2010 1:35:17 PM EDT
[Last Edit: 3/9/2010 4:04:51 PM EDT by pavlovwolf]
How is the battlesight zero for each caliber determined. Is a vital zone in inches used and then the data from the ballistics of the cartridge used to determine the yardage that bullet can stay within that zone? I know what is is for the 5.56 NATO, 7.62x51 NATO, 7.62x39, and others that are listed just about everywhere. What I need is for the 6.8. I'm basing this on a 90gr projectile with a muzzle velocity of 2900fps, and a ballistic coefficient of .275. Speer TNT as loaded by SSA in their combat load. I will probably just match that for my handloads, or just exceed it, but no more than another 100fps. There are other bullets coming on line now that will be in the 100gr range that have a much higher b.c., and I will most likely switch over, but right now I have 650 90gr TNTs to load up. Thanks
Link Posted: 3/9/2010 4:05:55 PM EDT
What factors do they use to determine this?
Link Posted: 3/9/2010 4:07:31 PM EDT
It's based on bullet compensation for particular sights.
Link Posted: 3/9/2010 4:08:27 PM EDT
Math. They use math.
Link Posted: 3/9/2010 4:09:35 PM EDT
they pick #s out of a hat
Link Posted: 3/9/2010 4:11:17 PM EDT
Originally Posted By southfloridaguns:
Math. They use math.


+1

Check this out
Link Posted: 3/9/2010 4:14:12 PM EDT
Originally Posted By Chris19delta:
they pick #s out of a hat


Yes, they do, based in the liklihood of that particular setting to inflict casualties on the enemy by semi-trained marksmen.


(That goes for Marines, too. The Basic training marksmanship period USED to be three weeks. When you think about it, they ought to go back to that.)

Link Posted: 3/9/2010 4:14:51 PM EDT
Math and then they verify it by shooting it. That is how I do it too.
Link Posted: 3/9/2010 4:17:16 PM EDT
[Last Edit: 3/9/2010 4:21:31 PM EDT by Rob762]
http://www.biggameinfo.com/BalCalc.aspx

This will calculate Max PBR for your bullet/velocity choice

ETA:  At that combination, the calculator spits out zeroing at 2.7" high at 100 yards for a max point blank range of 270 yards
Link Posted: 3/9/2010 4:30:43 PM EDT
Originally Posted By southfloridaguns:
Math. They use math.


THis. And something to do with the two crossover points within given practical ballisitc ranges isn't it? Know POA/POI for two given distances that are practical for guestimation?

Link Posted: 3/9/2010 4:53:17 PM EDT
I can do the math, and I understand trajectory. I can get the correct zero distance using a specific size vital zone. I normally use 4 inches for hunting.  I just want to know what size in inches the vital zone is that the army uses to determine what range the weapon should be zeroed at. They have to have a specific number that they want the bullet to travel within, no higher than and no lower than that will determine the maximum distance at which the bsz will be effective. Unless they use another method, and I'm trying to figure that out. I can't find it anywhere on the web. I could reverse engineer the bsz of a cartridge where that info is established. That would allow me to see the maximum travel above and below the point of aim out to the bsz, but that would be too easy. I thought maybe someone knew the answer. I'm sure someone here does.
Link Posted: 3/10/2010 6:21:26 AM EDT
Is there anyone that knows the exact method that they use? Could it have something to do with average engagement distance, and then using the cartridges external ballistics to calculate the flattest trajectory from the muzzle to the distance specified?
Link Posted: 3/10/2010 6:47:26 AM EDT
I believe the way they figure it is that they want BZO that provides a flat enough trajectory that you don't really have to think about adjusting for bullet drop until you get out past a certain distance.

For example, with a 50/250 BZO on an M16, the bullet will hit within +or- 2" of the POA out to 300 meters.  This means that for high-intensity combat, if the grunt on the ground aims for the vital area on the target, he is going to hit it if the target is within 300 meters.  Beyond that, he has a little more space to be able to take thoughtful, calculated shots and compensate for the drop.
Link Posted: 3/10/2010 7:17:40 AM EDT
I have that Raoc, but thanks for the input. I'm trying to find out what that plus or minus figure is. If I know that, I can calculate it for my setup. I can't find it. Maybe your search foo is better than mine and you can find it. Like I said before, I have a feeling that they use a larger vital zone than a hunter might since they are just looking for a center mass hit and not necessarily a clean kill, but it still has to be small enough that some modicum of accuracy can be achieved as well. My other thought is that average engagement distance may also be involved, say 300-400 yards or meters, and then you would calculate the flattest trajectory to that distance. Thanks for the input so far guys. There has to be some info somewhere that states they're process.
Link Posted: 3/10/2010 7:54:18 AM EDT
[Last Edit: 3/10/2010 7:55:43 AM EDT by brain]
..I'm confused, I shoulda paid better attention in school
Link Posted: 3/10/2010 8:07:18 AM EDT
)n the 6.8 forums they were talking of using a 25 yd zero for 115gr. to get a second cross over at 300 yds IIRC. Can always test/run it out yourself after the 25 yd zero if you've got the means for the distance/ range .
Link Posted: 3/10/2010 11:23:26 AM EDT
Thanks. That's about what I was looking at doing. I was just wondering exactly how the mil decided on the furthest distance in their formula. I'm getting a battlesight zero of about 290 yards with a 5 inch vital zone. I wold cross the line first at 20 yards, max height occurs at 155 yards, and it's 5 inches low at 325yardsl That might be best for this round. If I give it a 4 inch zone it would be a bit shorter, and if I go 6 it will be a tad longer. I guess 5 inches is best in this case. I'll be 17.9 inches,about 4 moa at 400,and 45.6 inches, about 8.7 moa at 500. The newer projos coming out with b.c. in the .475 range will really tighten things up. I don't know if it's possible to get anything with sufficient weight to get to that really happy place at the .500+ b.c. range, and still fit in the mag.
Link Posted: 3/10/2010 11:28:28 AM EDT
With a 100 gr and a b.c. of .475, which I've seen or seem to have seen discussed possibly coming from Sierra soon, you wouldn't see but 11.3 inches at 400 yards,  and at 500 you would only get 30 inches of drop if you use around 300 yards (290) as your battle sight zero, with 5 inches as your vital zone.
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