Danger Space

What is it and why is it worth knowing?

 

Danger Space is essentially the punch line to some basic exterior ballistic analysis. It was a concept taught to Snipers 10 to 15 yrs ago to give them the analytical tools to make good decisions about whether the shot they were about to take was feasible. Danger Space in simplest terms is the beaten zone created by your trajectory with error. Traditionally, the biggest error a long-range shooter faced was range to target and wind. Before widespread use of quality LRF’s, Mil-Ranging a target was the common method to determine distance. It was highly subjective and there was always a certain amount of distance error involved. Defining the potential beaten zone in yards allowed the shooter to understand the likelihood of hitting his target. It goes like this.

Say you’re shooting a 2 MOA target at 800yds at a match in which you know the match director uses a pretty sloppy LRF to provide ranges to the RO’s or worse yet, shoots the target and based on his dope determines what the range must have been. How much distance error can you have and still hit the target? Well, there a few variables involved.

For the sake of a demonstration, we’ll say we’re shooting a 6mm bullet at 3000fps with a G1 BC of .600. At 800yds your dope is 4.3 mrads. How much error do you have on that plate? The first step is determining the size of the plate in Mrad so you can define error above and below the mathematical POI. A 2 MOA plate at 800yds is 29” or .56 mrad tall. So, that means the shooter has .28 mrad of error above and below your mathematical POI. That means you could hit the plate (mathematically) with a 4.02 or 4.58 mrad hold. Add or subtract that error in Mrad from the shooters data to find the lowest or highest possible data to still hit the target.

Danger Space

So, what are your ranges for 4.02 and 4.58 mrad dope? Your ballistic solver tells you 4.02 is a 766yd data and 4.58 mrad hold is 822yd data. Your error range is the difference between 766 and 822: 66yds. That’s your danger space for that target, at that range, using that load. You could, mathematically, chip the bottom or top of that plate using data for anywhere from 766yds to 822yds. Clear as mud?

Danger Space 2

So we’re not Snipers and we’re going to shoot at every target at the match, no decision about it. Why do I care about danger space? Well, it answers the question, “Should I run my 6 Creedmoor at the top accuracy node or sandbag it at the lower accuracy node around 3000fps with a slow burning powder and hope to get longer life?”. “Should I shoot a BR or a Dasher for the extra 100fps?” Let’s take a look. What if we pushed that 6 Creed to 3150fps, assuming that’s about where the next accuracy node is.

Running all the previous data but at 3150fps what are my error ranges? Running the simulation on my AB 5700 Elite I get a 74yd error tolerance. 8 yds more than the lower accuracy node at 3000fps. A 150 fps increase in speed nets 8 more yards of error in incorrect distance.

Danger Space 3

Ya, but what about wind, right? That’s what really counts. Well, there is such a thing a windage danger space on target too. Just apply the error horizontally and in mph instead of vertically in yards. Let’s do it!

A 14” plate at 700yds is still .56 mrad across. Setting my ballistic solver to 1 mph of wind I learn that at 800yds a 1 mph wind will blow my bullet .13 mrad. Let’s just round that off to .1 mrad for beer math. By defining a 1mph wind I can determine how many mph wide my plate is. Just like yards but in mph.

My plate is 5 1/2 mph wide at 3000fps. Well, how about at 3150fps? A gain of 150 fps gets me .01mrads of drift for a 1 mph wind. My drift at 3150 fps is .12 mrads. Essentially, the plate is still 5 1/2 mph wide. Let’s see what the 10 mph number is. 3000fps - .98mrads, 3150fps - .90mrads. A net gain of .08 mrads. Less than 1 mph. I can’t make a different wind call from 3000fps to 3150fps. 

Let’s put that into a scenario to see how it plays out. I’m running and gunning on a gnarly Pikes Peak Precision 100 sec. par time stage and the wind is truly blowing steady 10 mph in that angry Ft. Carson wind (because it has to come in on a Saturday for the match). I’m getting heckled by the crowd and don’t see the mirage clearly and think the wind is blowing 5 - 8 mph, so I go with 7 mph for my call. Will I hit the plate? Who knows, because I totally shanked the trigger pull….

I recently did this analysis for my 6 SLR shooting 115 RBT DTACs when I signed up for the High Country Precision - Team Assault match. Since most matches provide ranges I already knew sandbagging the cartridge was worth the barrel life. I considered running at a higher node since this match involved unknown distances. Enjoying a 16oz Banquet, I ran the numbers and to my surprise there was no immediate ballistic advantage to running the barrel hard for a couple of hundred rounds. There are a few ballistic solvers that provide danger space for distance in the range card, like JBM. I haven’t vetted their math; I’m sure its accurate but I prefer to use the ballistic solver that I have trued and run my rifle from. Additionally, JBM doesn’t provide the wind analysis. Understanding the concept of danger space is different from reading a table pumped out by hitting “Enter” and gives a thoughtful long-range precision rifle shooter the context to make good decisions, whether in the field or at the match.