I have thought about sharing this information for years. It used to be a secret formula, but I can tell you this. I am terrible at math. I would have failed math class in high school if not for a friend doing my work for me, let alone understanding any geometry or advanced math. Yet, I was able to figure this out. I talked to a few other instructors, who said they do not teach this unless it's for military training. However, I have seen some PRS matches have a loophole stage and found resources online explaining how looping hole shooting is done. So, we have some constants: the center of the barrel, the distance to the loophole (for this formula, I chose 12 feet), and the scope height. Technically, the scope height will change from rifle to rifle, but if I can figure out a formula for these points, then I can figure out a formula for the scope height. The distance to the loophole can also change, but if I have a formula for the change in scope height, I can also find one for the distance to the loophole. I fumbled around with some numbers and came up with this formula, so why not share it as well?
What is tactical loophole shooting?
A loophole in this term is a small hole that would be used to shoot through. In a military application, a team member would knock a hole in the wall or use a hole from previous damage. Using a loophole helps to conceal the report of the shot while having complete cover and concealment of a recon or sniper team. A sniper team in an urban environment would likely be at the end of a long street in a shot-up building as their FFP. A team member would knock a hole in the wall large enough to observe the target area. The shooter would likely set up toward the back of the room, firing through the loophole. Using a silencer will minimize the weapon system's report and protect the team's hearing inside the room. The room itself will act as a second barrier to the report of the shot and keep the team fully concealed from observation, such as spotting scopes, thermal, and any incoming small arms fire. This means the team can see the enemy, but the enemy can't see them.
Geometry
The loophole formula is simple geometry or trigonometry. I honestly don't know. Remember, I'm bad at math.
We have 3 points of interest the we need to collect data on: The scope, the bore, and the loophole.
We first need to know the relationship between the scope and bore. This relationship is referred to as height over bore (HB) or scope height. We need to figure out the distance from the center of the bore to the center of the scope. On the scope, I use the center right where the turret is. Take your time and get this as accurate as possible. For my firearm, my height over the bore is 1.75 inches.
Next, we need to know how far the loophole is in feet from the point of the barrel right under where we measured the scope. For this example, I use 12 feet.
The final step is to find our bore height in mils. We'll take our scope height in Inches x 25.4.
Our scope height is 1.75 inches x 25.4 = 44.45 (45 rounded). For this formula and this gun, our constant is C = 45
The Formula
BH x C / distance to loophole = mils - DOPE
1.75 x 45 / 12 = 6.56 mils - dope
Next, subtract your Dope from 6.56
at 500 yards, my Dope is 2.8 mils
6.56 - 2.8 = 3.76 mils
Our bullet will clear the loophole if we have 3.76 mils of clearance. This formula does not account for any cant built into the rings or mount. If you have more than 0 moa base, this gives you more room for error.
This formula is exact, and 1.75 scope height is the lowest I see on long-range rifles. 2.5 to 3 inches is more common in my experience. Because of this, I edited the formula to be easier to memorize. Using a constant of 82 gives us a bore height of 3.3 inches. Using this formula will work on any rifle and gives us maximum clearance.
BH x 80 / distance to loophole - Dope
1.75 x 80 / 12 = 11.66 - 2.8 = 8.8 mils
Remember, 12 feet is very close to our loophole, so 8.8 mils sounds like a lot, but up close at 12 feet, 8.8 mils is just over 1 inch of adjustment.
Using these formulas, you can shoot through even smaller holes under an inch. The smaller the loophole, the less field of view you have on your target area. The closer to the loophole, the more exact you have to be, as you will have less room for error. We can also create other loopholes, but they would expose one to thermal observation devices. However, there are solutions for that as well, but that is a different blog.
Real World Application
Let's put ourselves in a real-world situation. You live in a nice neighborhood just outside the city. There has been some civil unrest nearby, rioting, and fires, and this mob of thieves hell-bent on hurting people is slowly pouring into neighborhoods outside the city. You have been paying attention to the news so your family is prepared. You have a plan, and it's time to act. Hopefully, you have some like-minded neighbors and a plan in place. Part of the plan involves a neighbor on watch. Your phone rings and this neighbor lets you know the hell-bent crowd is now entering your neighborhood. Unfortunately, the police are just standing by and not stopping these crowds from burning down businesses. You want to stop this, but you also don't want to make yourself a target, as you have your beautiful wife and kids in the house, and keeping them safe is your first priority.
You're set up on the chair just behind the dining table, looking through the window that is open about 2 inches. The curtains are just slightly open, casting a shadow on the window and allowing you to see out, but no one can see in. The slightly open curtains give you just enough room to observe the street leading into your neighborhood. You observe the crowd busting out the windows of the cars on the street and setting fires on the vehicles as they move on to vandalizing houses and kicking in doors. You have eyes on the target of a young-looking male in a red hoodie and blue jeans as he is coming out of the house that he just kicked in the door and moving to a second house. As you aim, your heart is racing. You exhale slowly and deliberately to your natural respiratory pause. With a slow press to the trigger, the suspect is no longer a threat. In confusion, the rest of the crowd panicked and took off running. The shot was heard but came from a place that no one could identify. The suspect in the red hoodie is lucky to still have his life run like the coward he is. Your shot to the brick mailbox right in front of him made him realize that this is not the neighborhood.
In the aftermath, one of the people in the crowd had the audacity to call the police and report shots fired. And, of course, the police show up to investigate. However, with the loophole you created using the front door, no one could tell where the shot came from. You and your team of like-minded neighbors also reported not knowing anything.
Practice
You don't have to have a target set up at a long distance to practice loophole shooting. You can practice this at short ranges. I practice loophole shooting using a pizza box with a 2x2 hole cut into it. I'll place rocks in front and behind to hold the box top upward. I'll lie in the prone position 12 feet away and run the formula using different distances to dial in my Dope. The main thing I'm looking for is that the bullet clears the loophole. I can also hold every shot lower to see how many mils off I can be before striking the box. This method gives me confirmation that my formula and math are correct.
The Overwatch