.308 at 1700 yards

[Davidk]

The correction was 30 mils. I believe that a mil is 3.438 MOA so it translates to 103 MOA

I dialed 20mil into the scope and used the 10mil line in the reticle. I prefer using turrets as little as possible due to mechanical inaccuracies.

You need a scope with lots of elevation adjustment.

 

[cockpitbob]

30mils?!?!?!? Saying it a different way, you were aiming 144 feet high
Cool

 

[bricktop]

I believe that OBRs are 1:11. Todd's personal OBR has a custom barrel with 1:7. Was using Hornady Superformance 178s.

You are right, once bullets go subsonic, they loose BC continually. Not being able to shoot past subsonic is a common myth. The instructor for my last long range class, a Marine Scout Sniper, said that 1200 is the limit for 308s as they are not controllable in subsonic flight--Not true!

The BC of a bullet is a constant vs. velocity, if you're using the correct reference (i.e. G7 for a boat-tail type). In the transonic region (mach 1.0-1.2), the shockwave produced by the bullet beings to catch up and disrupt the flow of air along the boat-tail, potentially leading to bullet instability and poor accuracy. Properly designed bullets can mitigate the effect, some bullets are specifically designed with this in mind (i.e. Berger Juggernauts). Subsonic rounds don't have this concern, as there was no shockwave produced to disrupt the bullet.

 

[Davidk]

30mils?!?!?!? Saying it a different way, you were aiming 144 feet high
Cool

Yup, 30 mils. By my calculations, I was aiming 158 feet high .

1.047 inches per MOA at 100 yd x 17.6 (1760 yards) = 18.4272 inches per MOA at 1760 yards.
103 moa at 1760 yards, so the hold over =1898 inches = 158 feet
My calculation correct?

 

[andrew]

David, I'm curious, how many MOA of come-up did you have cranked in at 1,600y? I've never bothered to generate come-up tables that far out but the bullet must have been coming down at a pretty steep angle.

Wicked jealous.

I was going to ask the same question. The hold-over must have made the shot look like a mortar round coming in.

 

[Davidk]

The BC of a bullet is a constant vs. velocity, if you're using the correct reference (i.e. G7 for a boat-tail type). In the transonic region (mach 1.0-1.2), the shockwave produced by the bullet beings to catch up and disrupt the flow of air along the boat-tail, potentially leading to bullet instability and poor accuracy. Properly designed bullets can mitigate the effect, some bullets are specifically designed with this in mind (i.e. Berger Juggernauts). Subsonic rounds don't have this concern, as there was no shockwave produced to disrupt the bullet.

At subsonic speeds, bullets loose stability and therefore their BC drops. The longer they travel in subsonic flight, the more the BC drops due to increasing instability.

 

[ntomsw]

This thread is awesome.

Kudos to you.

 

[DrRansom]

At subsonic speeds, bullets loose stability and therefore their BC drops. The longer they travel in subsonic flight, the more the BC drops due to increasing instability.

Not necessarily. It's not so much that there is a guarantee of instability, but rather the effect is inconsistent. As bricktop correctly said, modern bullets can account for this and make the consistency better, which is ultimately all that counts.

Further, bullet BCs never "drop". A bullet can become unstable, and the flight path can alter accordingly, but the BC of the bullet does not change.

 

[bricktop]

At subsonic speeds, bullets loose stability and therefore their BC drops. The longer they travel in subsonic flight, the more the BC drops due to increasing instability.

If that were true then all subsonic ammunition would be useless, but it can be quite accurate.

BC is a constant and independent from stability - it is a function of bullet geometry. An unstable bullet can produce trajectories that can in some cases appear to be a drop in BC, though, but it's not what is really happening.

 

[Davidk]

This is concerning a bullet designed for supersonic, not subsonic flight.

If a bullet increases instability as it travels in subsonic flight, how can its BC not drop accordingly?

 

[Davidk]

Not necessarily. It's not so much that there is a guarantee of instability, but rather the effect is inconsistent. As bricktop correctly said, modern bullets can account for this and make the consistency better, which is ultimately all that counts.

Further, bullet BCs never "drop". A bullet can become unstable, and the flight path can alter accordingly, but the BC of the bullet does not change.

Transonic and subsonic flight trajectory is not my area of expertise. The info I am including here came from Todd Hodnett who figured out how calculate trajectory correctly at great distances after the bullet transitions to subsonic flight.

 

[DrRansom]

If a bullet increases stability as it travels in subsonic flight

Nobody is asserting this? It's not a matter of increasing stability, it's a matter of consistently retaining stability?

how can its BC not drop accordingly?

BC is a constant and independent from stability - it is a function of bullet geometry.

 

[Davidk]

Nobody is asserting this? It's not a matter of increasing stability, it's a matter of consistently retaining stability?

it was a typo, I corrected the word to "instability" The bullet's instability increases as it travels in subsonic flight

 

[mav]

2400 feet. Why not at sea level?

Higher elevation, less drop off in velocity for a given distance, squeeze out a bit more range. I'm surprised you were that low.

Using my ballistics calculator for 168gr Federal Match 308 (what I shoot), the difference between shooting at sea level and 2400 feet is approx 9MOA in bullet drop at 1600 yards. Another factor is angle to target... that pic you posted looks like you're at a higher elevation than what you're shooting. Was that the case?

 

[Ranger007]

Hmmmmmmmm

 

[Davidk]

Higher elevation, less drop off in velocity for a given distance, squeeze out a bit more range. I'm surprised you were that low.

Using my ballistics calculator for 168gr Federal Match 308 (what I shoot), the difference between shooting at sea level and 2400 feet is approx 9MOA in bullet drop at 1600 yards. Another factor is angle to target... that pic you posted looks like you're at a higher elevation than what you're shooting. Was that the case?

Agreed, you just have to compensate for the difference. The targets were a little lower but not enough to compensate at that distance.

 

[mav]

Agreed, you just have to compensate for the difference. The targets were a little lower but not enough to compensate at that distance.

Cool stuff. I would definitely be interested in a class like that. Heck, I'd be happy to find a 1000 yard range to shoot at occasionally within easy driving of MA.

 

[Mass-diver]

Great thread, 1600 with a .308 is the big leagues for sure!!

 

[Davidk]

Cool stuff. I would definitely be interested in a class like that. Heck, I'd be happy to find a 1000 yard range to shoot at occasionally within easy driving of MA.

Unfortunately, the closest 1000 yard range that I know of is in NY

 

[ChevyGuy91]

What does that class cost to take?

Not that I think I could even carry that dudes rifle, never mind keep up in that class, I have been interested since I watched the Magpul dvd.

 

[rkwjunior]

Just came back from a rifle class with Todd Hodnett at Accuracy 1st in TX.

Hit 16 inch plates at 1600 meters (1 mile) with .308s! It was awesome!

View attachment 62627

That pic is awesome!!!

Freedom at it's finest for sure!!!!

Jealousy isn't the word.

 

[cekim]

Put a Porsche out there, you wont hit a damn thing.

Is NES anti-Porsche?

 

[wahsben]

I have the Magpul long range precision shooting disc that is with Todd.
It sure would be nice to get out there.

 

[therealkdc]

this is awesome

 

[TheRoland]

Higher elevation, less drop off in velocity for a given distance, squeeze out a bit more range. I'm surprised you were that low.

Using my ballistics calculator for 168gr Federal Match 308 (what I shoot), the difference between shooting at sea level and 2400 feet is approx 9MOA in bullet drop at 1600 yards. Another factor is angle to target... that pic you posted looks like you're at a higher elevation than what you're shooting. Was that the case?

The trick is that some projectiles don't do well in the transonic zone. Shooting the 168gr SMK out to 1000 is considerably harder than others because it loses stability. The 178 BTHP David used here is much better when it slows down.

I'd love to take a class like this or like those offered by RiflesOnly, but man, Todd takes pushing the Horus very seriously.

 

[andy t]

I'd love to take a class like this or like those offered by RiflesOnly, but man, Todd takes pushing the Horus very seriously.

Makes sense, since he works for them.
Another interesting read: TREMOR 2 specifications - snipershide

 

[andy t]

Unfortunately, the closest 1000 yard range that I know of is in NY

Sig Sauer Academy has a 1000 yard range, that you can shoot as part of their "class".

 

[Davidk]

Todd "pushes" the Horus because he designed the TReMoR II reticle and partnered with Horus on it. My experience is that it is MUCH faster than dialing turrets and more accurate since here is no mechanical errors.

Todd lives what he preaches as well.

 

[TheRoland]

Todd "pushes" the Horus because he designed the TReMoR II reticle and partnered with Horus on it.

Well, sure. But in some contexts, like the Magpul DVD, it's really front-and-center. Someone just watching the DVD might be shocked to discover Horus reticules arn't all that popular in long-range competition.

My experience is that it is MUCH faster than dialing turrets

But they're not without downsides, no? They're very visually busy; finding the proper line, for some people, can be potentially error-prone.

and more accurate since here is no mechanical errors.

Have you had problems with erectors in the 1600$ price range?


Not saying they're bad or anything (I personally love the H59) but just offering some perspective.

 

[Davidk]

Well, sure.



But they're not without downsides, no? They're very visually busy; finding the proper line, for some people, can be potentially error-prone.



Have you had problems with erectors in the 1600$ price range?

Horus reticle are busy when you look at the reticle as a whole. When you get behind the scope on a target all the markings seem to disappear and it is very easy to concentrate on the correct marking and your target. I hated the reticle until I actually used it. I love it now and would never go back.

Wind is incredible easy. The TReMoR II reticle has wind markings that relate to 3,4, or 5 mph depending on your bullet's velocity and BC (caliber mostly.) If your dot is 4mph and you have a 12mph wind, hold 3 dots. 14 mph, hold 3.5 dots. No needed to calculate hold values.

Todd told me horror stories about mechanical errors in expensive scopes, much higher than $1600. I think it was a $5000 Zeiss that he said was his worst. When error occur, most often, when you dial large amounts you don't get what you dialed. Ex. Dial 10mils and get 10.8. Another scope you may get 9.2. That's very important at long distances. The worst errors are inconsistent mechanics.