The Slope Doper
(Slope Angles Made Easy!)

< 1999
By Scott Powers , photo by Dave Croyle

I recently received a new product just entering the tactical shooting market, the Slope Doper. The principle behind the Slope Doper is simple, and well known to those who have taken any long-range rifle course. When shooting up or down hill, you must compensate your aim based on a reasonably accurate estimation of the angle you are firing. One accepted way of doing this has been to use a simple children's or draftsman's protractor, with a weighted string attached. Holding the protractor to match the angle you observe, you then read the scale at the point the weighted string indicates. This gives you a close approximation of the angle of the hill. With this figure, you can then use a mathematical factor to divide the actual range by, and adjust fire accordingly.

The old adage when shooting up or down hill is to "Aim low". With a protractor, you can gauge approximately how low. Yet, until the introduction of the Slope Doper, you were limited by the flimsy construction of plastic protractors, along with their other downsides, detailed below.

The Slope Doper is unique in that it is purpose-designed and built for the tactical shooter or hunting enthusiast. Made of a photo-etched aluminum plate, the indicator is black with white markings. The Slope Doper measures only 2.25" by 4", or not much bigger than a business card. It fits easily into a pocket, where, due to its construction, it will remain relatively safe from the destruction that can befall plastic. This is quite an advantage over standard plastic protractors, because they are generally made of a hard brittle plastic that will crack with age and exposure to sunlight. The Slope Doper also has some unique shooting-specific markings on it, making it ideal for the hunter or sniper. On the black face you will find easily read white markings to indicate slope angle, angle multiplication factor and the proper mathematical formula to use the tool. A weighted string hangs from the top center of the card. When placed along the axis of your aimed rifle, the string will indicate the angle your are sighted along. If you are not employing the rifle, you can simply sight over the top of the card, visually matching the Slope Doper to the angle of the hill.The Slope Doper, as seen next to one round of 
M118 Special BallJust above the Slope Angle reading is the Slope Angle Factor for that slope. Use of the tool is quite simple and can be accomplished with an economy of movement. For example: You have either sighted a target down-slope from your position, or you anticipate a target appearing there. Using your scope, you determine that the range is 700 yards. With your .308 rifle, you would normally dial up 22.25 minutes of angle (MOA) on your elevation turret, but as you are shooting down-slope, you know that the range will be, in effect, reduced. You or your spotter lay the Slope Doper along the axis of the bore, and read off a figure of, in this case, 30 degrees. Above the angle you read a Slope Angle Factor of point 87. What this means is that to hit point of aim, point of impact, all you need do is multiply 700 yards by .87 to calculate your new scope zero, which in this case is 609 yards. Your sniper data card indicates this will require roughly 18 MOA up from your 100-yard zero. You dial in, aim dead on and fire.

For a police marksman, working in an urban environment, this would appear to be an excellent tool - Particularly for the officer who might find himself on a high rooftop overlooking a crime scene. A 70-yard line of sight shot, taken on a 60-degree downslope, would equal a 35-yard shot. Not a big difference. But if your shot happens to cover several city blocks, the range becomes very important. A shot taken on a 30-degree angle at 300 yards translates into roughly 260 yards. Enough to miss the shot. This tool makes judging the angle and correction a snap.

The Slope Doper is still in Generation 1.0. The second generation tool, and the one most likely to hit the market, will replace the string with a tapered bicycle spoke, which will in essence, give you an indestructible pointer. If it does happen to break off or get lost in the field, you can still easily replace it with a good string. Other improvements will include changing the current rectangular shape to one approximating the curvature of the protractor dial, but still leaving a flat spot on the apex to facilitate aligning the tool with your rifles stock, scope top, or barrel. Speaking of the protractor: those of you familiar with home-modified tools of this nature are aware of the problem with all plastic protractors. At the bottom of the arch, when held upside down to use for judging slope, the 90-degree indication is where Zero should be. You always have to mentally convert the indicated angle to the true angle. With the Slope Doper, this extra step is no longer an issue as the apex of the curve is marked zero degrees, with 90 degrees being at the upper edges of the tool.

Provided along with the tool are two adhesive-backed cards, with mil formulas showing constants for yards, and meters. These handy cards can be placed in your data book for quick reference, or on the back of the Slope Doper.

I can heartily recommend this tool and will be keeping my sample under lock and key as my shooting partner is eyeing it covetously as I write this review. Sure, you could make a slope indicator out of a cheap school protractor, swiped from your 7th grade rug rat, but it will not hold up as well, does not have the Slope Angle Factors there in plain view for those of us with failing memories, and is not nearly as "trick!" I ask you, what hunter does not enjoy a few tricks now and then? At least this gadget actually has a very useful purpose, which is more than I can say for some of the hunting "tools" I have succumbed to purchasing over the last few years!

The tool is just entering the market and is being manufactured on a small scale at this time. While price is still under consideration, expect to see a retail price of $20.00 plus shipping. This is not bad considering the quality construction of the Slope Doper. For further information, availability and pricing contact the maker, David P. Rolls, of Burlington West Virginia. You can reach him via e-mail at:

To purchase units, contact Rod Ryan at Storm Mountain Training Center. You can reach him via e-mail at:

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