The Saga Of The Uphill/Downhill Shot, Part I
by Edd Pungubwe Woslum
©Copyright 2010, Precision Shooting Magazine
We had spotted the buck from the top of the steep canyon about 45 minutes previously and had since that moment been slipping and sliding down the rock strewn hillside, while trying to stay hidden from our still unsuspecting target. This stalk down the treacherous slope was more reminiscent of a sheep hunt than the pursuit of a whitetail deer but as I had explained previously to my present hunting partner six months ago, our whitetail in the Salmon River breaks have habits more akin to mule deer than their Virginianes brethren.
Randy Brooks and Tilly the tracking dog. This buck was taken on a steep downhill shot at 400 yards.
My friend Randy Brooks (of Barnes Bullets fame) and I had been planning this excursion for a couple of years. Our plan for this outing was to mix a bit of scientific research, by way of running a few tests with the relatively new 150 grain .284 diameter Tipped Triple Shock bullets, with a great deal of pleasure enjoying a Northern Idaho hunting adventure.
As Randy was on a rather tight schedule, the day before his arrival I conducted the accuracy phase of the test by shooting multiple groups at 100 to 300 yards with the blue tipped projectile. All of these tests were completed with my old standby .280 Ackley, which is mounted with a Leupold VX3 4.5 to 14 scope that has a target turret for vertical adjustment. As all of the groups shot this day were well under the magic one MOA mark I considered this phase of the project to be well and thoroughly done.
For the past 20 years our method for sighting in at the various distances is to wrap a piece of masking tape around the turret, then shoot the gun at each distance from 100 to 600 yards and make a mark on the tape for each distance. Sort of low tech but very effective. I had a few days back completed this task and was now ready for Randy’s arrival. As our 1000 yard range is conveniently located literally right out our back door, he could upon arrival step out on the deck, take some familiarity shots and be good to go. One other part of the test that I failed to mention, some three weeks back I had purchased a new Leu-pold TBR (True Ballistic Range) 1000, laser range finder, with built in illuminated slope dope indicator and I couldn’t wait to use it on an actual hunt. Our tests on the range indicated this instrument to be accurate to plus or minus one yard.
Our stalk down the side of the mountain, due to the loose rocks and the 40 degree slope of the terrain, sounded more like a cavalry charge than a ninja sneak. Consequently at about 400 yards from the buck we decided we had better set up for a shot before we frightened the still bedded deer clear into Montana. Down went my backpack and Randy made ready to launch one down range. I took a quick read on the TBR, it indicated 404 actual yards to the critter, and a TBR reading of 350 yards. I reached over like a good little spotter and turned the scope to the 350 mark. “Send it” said I, as I stared through my 10 power glasses. At the shot the buck only pricked his ears as the bullet went six inches over his back. I then swapped the binos for the TBR and took another bearing. This one read the same as the previous. “Send another one,” I again said with confidence. At the report the critter showed a little more concern than he had at the previous, as the bullet again hit the dirt in the exact same spot as the last. Keep in mind my friend is a very accomplished rifleman and even though he said not a word, I’m sure at this point, he was no doubt wondering about my dubious skills as a spotter. It was obvious at this point that what I was doing wasn’t working so I reached over and turned the turret down six clicks. This time at the shot the buck folded on the spot.
The next day Randy went home happy but we were still pondering the ballistic weirdness that had taken place the previous day. Two days after his departure, I had the rare opportunity to actually hunt a deer for myself. Barely an hour after daylight I spotted a nice buck that was bedded exactly 400 yards from my perch on the side of the mountain and déjàvu he was 30 degrees downhill. Just like our previous encounter my new electronic wonder tool indicated a TBR of 350. One of our basic hunting rules on the ranch is that we never take a long range shot at a game animal unless we have a competent spotter in place. 30 minutes after the initial sighting my wife Leanne was firmly planted behind me with her spotting scope cranked up to 40 power.
After several poorly placed downhill shots, we set up this target at 400 yards, at 30 degrees downhill. This 3 shot group is about 6 inches higher than point of aim. There was a 10-12 MPH headwind at the time which may account for some of the disparity.
At the shot the deer never even blinked. “Six inches over his back,” said Leanne. “What happened? I must have shanked the shot,” I thought as I squirmed a little tighter into my back pack rest. One more round down range and it was the same result. Just as with Randy’s buck, I then turned the turret down six clicks and dispatched the deer where he lay.
The next day Leanne was getting a bit weary of my lamenting about my poor shooting and slope doping and said “OK old man, get a target, your gun and all your other magic devices and let’s go recreate your shot. Two hours later we had an IPSC target, with an added blaze orange bull’s-eye in the middle, set up in the exact spot on which the deer had been bedded. We then climbed back up the mountain and plopped down the back pack. The range finder again indicated 400 yards to the target. The TBR repeated exactly its message from the previous day and showed 350 yards. We fired six shots from this position and went to check the target. Four of the shots were in a nice three inch cluster with the other two shots opening the group to about four and a half inches. Not bad I thought. The only problem was, the group was a full six inches above our orange bull. “What the Sam hell!”
Prior to acquiring our first laser range finder in 1992, our routine was to sight-in our hunting rifles to impact three inches high at 100 yards. Any target out to 300 yards we would then merely hold on and shoot, primitive but it worked. In 1992 the President of Leica Corporation gave me one of their new wonder tools called the Geovid. This device was incredibly accurate but weighed a ton and was usually left in the truck when we were out hunting. In the next 17 years we used a multitude of laser devices of various weights and description. When using these instruments our protocol on uphill/downhill shots was quite simple; if the slope was around 25 degrees or less we merely held a little low on the animal and fired. If the target was 30 degrees or more up or down, we would subtract 20 percent from the known distance and shoot. My family used these various methods of hold over/under during 45 years of hunting, in order to take over 500 animals of various taxonomical descriptions, so I guess they worked OK.
I’m not an electronic equipment junkie by any stretch but have always been keen on any innovation that will allow me or my clients to more effectively engage targets and cleanly dispatch an animal. When the TBR came along I was ecstatic. Here was a device that would allow us to consistently place lethal shots on mountain game animals with no guess work. This was the greatest scientific breakthrough since the telescopic sight. After using the TBR extensively in 2009 plus visiting on numerous occasions with the technical staff at Leupold, I am convinced without reservation that this is an extremely accurate tool and would be of great benefit to any serious hunter.
With that being said I still had a ballistic issue that demanded resolution. In order to better understand the problem I dug out all of my old notes from Art Pejsa et al and began my own research project that would have made Isaac Newton do a double back flip. When discussing this scientific issue with several of my industry acquaintances, the subject of temperature, altitude, barometric pressure and the like invariably came up. One of these enlightened souls was convinced that the disparity in point of impact was due to the shooter canting the barrel differently between the sight in shots and the shots in the field.
Leanne Woslum and great granddaughter Briella. These two are very pleased that we got this guy after several attempts.
A quick review of these dynamics is at this point no doubt in order. For those readers who are ballistically astute the following may be a bit ho hum but believe me the vast majority of the weekend hunters and even a few of the so-called tactical experts are grossly misinformed on these topics.
ALTITUDE DIFFERENTIAL – An altitude increase of 10,000 feet raises the point of impact for most bullets one inch at 300 yards. At 500 yards this becomes a correction of 5.5 inches.
TEMPERATURE DIFFERENTIAL – A temperature decrease of 50 degrees lowers the point of impact 2.5 inches at 500 yards. An increase of 106 degrees equals a ballistic change of one MOA.
GRAVITATIONAL INFLUENCE – Other than wind and the velocity of the projectile, this is the most influential of all the ballistic dynamics and the most often misunderstood.
The basic premise is that any object will fall from any height at a particular rate according to its mass. It matters not if that object is dropped from a platform or if it is propelled from a rifle barrel.
Hypothetically let’s say that you were to stand on an 18 foot platform and drop a 168 grain .308 bullet and that it took this bullet one second to drop the 18 feet. If one were to then load this same bullet in a cartridge that would propel it at 3000 fps from a rifle, it would still fall at that same rate i.e. 18 feet in one second. Gravity is gravity and you can’t fool Mother Nature (or should we say you can’t fool quantum physics).
The above hypothesis assumes that the barrel is oriented perfectly parallel with the earth’s surface. If one were to elevate or lower the muzzle of the rifle by 60 degrees, gravity would then no longer be working at 90 degrees to the bullet flight and the bullet would not drop as far in that given length of time. Now this is where the wicket gets a bit sticky. Most of the $20 uphill/downhill doping gizmos available today will accurately measure the angle of the shot and will just as accurately advise you what percentage factor should be applied in order to properly resolve the shot solution. All is good to this point but here is where they go awry.
Hypothesis – We have a steep downhill shot and the reading from our manual type inclinometer indicates it to be 60 degrees from the horizontal and that we should apply a factor of 50% in order to correctly impact the target. The 60 degrees is correct, and the 50% adjustment is correct. The instructions then tell you to apply the 50% factor to the actual distance to the target. Physicists will now tell us this application is completely 100% wrong. This is due to the manner in which we adjust our sights in order to compensate for bullet drop. At an angle of 60 degrees the component of gravitational force is one half of its vertical value, not one half of the distance to the target.
If we were to apply the above process to a hypothetical range situation it could read: distance to target = 300 yards, the slope is 60 degrees the percentage factor is 50. 50% of 300 = 150 therefore shoot the target as if it was 150 yards. This would be a big mistake.
The correct application of the slope dope is: The bullet drop from bore line to 300 yards is about 23 inches depending on the exact weight. In order to compensate for this bullet drop we must lower the reticle of the scope (so as to raise the barrel) the MOA equivalent to this correction factor. This equals about seven MOA.
In order to put this into a real life scenario, let’s use my .280 Ackley, shooting a 150 grain TSX bullet at 2900 fps, and using my Leupold 4.5 to 14 with ? minute clicks for sighting equipment. Our objective is to hit a 400 yard target on a 60 degree slope.
CORRECT APPLICATION – The scope adjustment required on the flat is 6.75 MOA or 27 clicks. Apply the 50% factor to this (.50 X 6.75) = 3.37 MOA. Actual come up clicks required 13.
INCORRECT APPLICATION – 50% of the distance (.50 X 400) = 200 yards, which is only 6 clicks up. This seven click difference between the two methods is equal to a seven inch disparity at point of impact.
Steve Adelmann, retired U. S. Army Sniper, and PS columnist, and I have discussed this issue extensively. Steve being of inquisitive mind and having dealt with this sort of problem on a daily basis, was more than willing to run some real life up/down slope problems through his various programs. Alas the results of these tests further confuse the issue. As Sergeant Major Adelman said in his most recent message to me: “The only issue these various programs agree on is when shooting uphill or downhill, your bullet will impact higher than it would if shooting on level ground.”
As far as practical application for a sniper in theater is concerned, Steve says that most snipers have worked out their own solutions to these problems and have the dope permanently affixed to their buttstock.
Using a standard U.S. sniper .308 load sighted dead on at 100 yards, Steve provided data from 10 different service manuals and computer programs including the U.S. Army’s, Marine Corp’s, and National Law Enforcement manual. An example of these data is as follows:
RESOURCE 150 yd. level hold 300 yd. 60 deg hold
Sierra Infinity Up .6 MOA Up 1.5 MOA
Trag MP Up .6 MOA Down .2 MOA
Special Forces Divide the
Manual measured range by 1/2
Quite obviously there is a huge difference of opinion on the solution to this ballistic issue.
After this heady discussion where does this leave me with the mystery of shooting too high on downhill targets? I haven’t the slightest clue!! But there is great hope for me yet. The technical folks at Leupold have agreed to come to Yellow Wolf and do an extensive test on all these issues. There are indeed gremlins about and we are going to ferret them out. Stay tuned.