why do shots drop more when shooting at a small incline at extreme range?

[Augustus]

I use Atrag it does not have a neg or *** slope function on it. As stated before I have shot the same range at 2000 plus yds from both ends. Uphill one way and downhill the other, the drops are the same.

I have not used the software you have and I don't feel qualified to argue with the solutions generated. I hope your software is FOS because if a 5 degree slope has that much difference in uphill vs downhill think what a much steeper angle would do.

I shot the 375 at 2500 yds and used the LOS distance, turned out the target was 4 to 5 degrees uphill. The center of the group was .2 mils high. I haven't shot any steep angles at ELR so I don't have any firsthand data.

 

[ajhardle]

When I enter incline values greater than 7 degrees the drop decreases as expected, but when the bullet has slowed so much the downhill shot needs less holdover than uphill. I assume it is because gravity is helping the trajectory downhill and slowing the bullet shot uphill. The effect of gravity is almost invisible when comparing incline angles at supersonic speed, but at slower speeds, gravity changes things. look at it this way, the rifleman's rule is explained by the effect of gravity is diminished by the angle because gravity pulls down, not 90 degrees away from the line of sight. Well, when shooting uphill, gravity is not only pulling away from the line of sight but also pulling away from the direction of travel (slowing it down). When shooting downhill, gravity still pulls the same away from the line of sight ( assuming a directly inverted angle, like 6 and -6 degrees) but instead of pulling away from the direction of travel it is now benefitting the bullets speed (not slowing down as much). Another perspective is to look at shot at 45 degrees. Only half the force of gravity pulls away from the line of sight. How much effect can the other have, and at what point is the effect large enough to notice? It is so small that it is imperceptible when shooting a 375 cheytac at 2000. noted. Let me remind, this is only noticeable at much slower speeds, but here of guys doing amazing things with .308 winchester's and 175 smk. Maybe those guys have witnessed this?

 

[ajhardle]

Maybe this is a complete waste of yours (and my) time. I'm going to go seat primers now. thanks for your input.

 

[Augustus]

There was a thread back in 2007 that discussed this issue. 6-5-07, Rifles Bullets Barrels Ballistics Forum, Uphill Downhill Corrections, Shawn Carlock.

Mr Perry Was contacted and asked about this issue, there is 12 pages of discussion and I have a headache. Look it up it's a pretty good read giving opinions on both sides of the issue.

 

[ajhardle]

Thanks for sending me to that thread. Mr. Perry states "there is no difference between uphill and downhill." This seems true at reasonable distances. Like 1000 yards for my .223 and 2500 yards for your .375. Alot has happened in 5 years, and I am curious as to what his answer is now. He also said coriolis is negligble. really????? I always combine spin drift and coriolis into my calculations, and believe me, it makes a difference.
I guess the only thing to do now is try it for myself and see how my results compare with predictions.
1st step: Get my .223 shooting through transonic. This might include a corrected b.c. for a .224 x 1.2" projectile going sideways.
2nd step: get my s.d. in low single digits on a day with zero wind.
or revert to plan B, which is to accept the fact that I will never shoot small enough groups at such extreme distances as to be able to acquire usable data.
I'll let you know if i make it past step 1 after fire season has ended.

 

[Augustus]

Anyone serious about ELR shooting should verify computer generated predictions through actual field tests. The best way to settle the uphill/downhill question is to shoot your particular Rd at the distances you expect to encounter.

If you have a range where you can shoot steep angles from both ends you should do so, that will tell you which theory is correct at that distance.

 

[ajhardle]

I believe I read you are using cutting edge. What b.c.(s) do you use? I have a 300 rum barrel sitting next to a rifle right now, but if that doesn't satisfy my desire, I will have to step up. I have had a hard time getting on board with solids. Do they perform as advertised?

 

[Augustus]

There has been a lot of hype surrounding the BCs of solids, the fiasco really kicked in gear several yrs ago when certain folks advertised the Viking 375 bullet to have a BC of 1.5, other folks scrambled to enter into the market with there own version of a wonder bullet. Everyone begin to realize the computer generated designs had problems, BCs were not living up to expectation and the more radical designs had stability problems.

There are several solid designs available that perform well, the only one that I can personally recommend is the Cutting Edge bullet. Dan at Cutting Edge lists the BCs a little higher than my experience with them suggests. There may be something in my system causing this or Cutting Edge may be a little too optimistic. Either way they are a very stable and consistent design.

I have banded the BC for the 425 gr, at 1000 .96, 1760 .95, 2000 .94, 2500 .93. Many folks have drank the cool-aid concerning high BC bullets and are unimpressed by these numbers. These are real numbers and not wishful thinking.

To put the BC flap in context, consider the 50 cal 750 gr. Amax. The BC on this bullet is around 1.0, the shape is not all that bad and it has twice the mass of most 375 bullets. Look back at the bullets that have been introduced on this site. Many has made claims of very high BCs. These claims quickly evaporate once they bullets get in the hands of competent and unbiased people.

The BS surrounding BC numbers has not been limited to solids. I you recall Berger stuck a .9 on the 300 gr 338. As soon as people started shooting it the numbers had to be revised back to a shade over .8

The short answer to your question as to whether solids perform as advertised, the short answer is some do, some don't, and the capabilities of some are grossly overstated.

 

[RMulhern]

Augustus

You're a man 'near and dear' to my heart....for telling it....just as it is! Those that wish to work strictly off of so-called 'published data' will have at times a rude awakening with actual shooting in the field and with correct record keeping will find that all that glitters....ain't gold!!

Good day sir!

 

[Augustus]

Sorry for the typos, If Mrs. Roberts was still alive I would be in trouble!!!! She was my English teacher, meaner than a snake if pushed but was one of the best teachers I have ever known.

 

[Shawn Carlock]

An interesting note about up/downhill shooting. You will shooting at extreme distance impact higher shooting uphill than you do downhill. I am talking about 15-20 degree shots here. Let's take for example that you are shooting 2000 yards and there is an elevation difference from you to the target of 2000 feet (cosine of .94 or so). You are shooting uphill, the station pressure at your position is 26.5", the station pressure at the target is roughly 24.5". The accurate shoot to pressure over the distance of the shot is 25.5". If you disreguard this averaging of the pressure over the distance of the shot (I do not know of any ballistic programs that do this for you) you will impact high because the air gets thinner from the time the bullet leaves the muzzle until it impacts. Note check the difference 1" of pressure makes with your round at 2000 yards. Of course the opposite of this is true shooting downhill at the same angle and distance you will impact lower due to the air getting thicker over the shot distance. Both uphill and down hill will shoot flatter than a horizonal distance fo 2000 yards but they will not be the same both up and down hill. This business of averaging the pressure over the distance of the shot is not to be taken lightly at loooooong distances. At 2750 yards and 2000' elevation difference failure to average pressure will result in about 8 feet difference in impact (witha 338 Edge +P). This is not just computed data, we shot and filmed this test for Send It volume 4. This also brings up a question about correct validation at long ranges shooting anything but completly flat shots. We have started teaching this pressure averaging in our extreme range classes and it has worked quite well. I hope I explained this clear enough.

This is not exactly answering the original posted question about small inclines but seemed like it had bearing on the thread. Hope this helps.

 

[ajhardle]

Thank you, Shawn. After reading your post from five years ago, I compared my ballistic data with cosine x trajectory, and that gets me accurate enough shots within the maximum distances I have been shooting with my .223(almost 1200) yards. But, none of us can accept the max distance we have been as the max we will go, so I always try to improve my knowledge, skill and equiptment. Most people take little things for granted that can upset a trajectory, like upwind, or a scope that moves less than .250 moa per click. These people assume the data is incorrect, but I think a professional will agree, if you put correct inputs in, the data is more accurate than a shooter in most cases.

 

[bigngreen]

Shawn, Patagonia ballistics and the Applied Ballistics programs will account for metro data change on an incline, those are the two that I've owned and confirmed this with the programer.

 

[Shawn Carlock]

Interesting, I wonder if they use the same averaging method or a progresive curve correction?