Bipod Prone Analysis

I started my analysis with the bipod prone position.  I did not have a rear bag on hand.  Once again, my rolled up nomex flight gloves (I don’t just shoot my rifle- I fly it) came to the rescue in the form of improvised rear support.  The ammo throughout the test, was a Black Hills loading of the Hornady 155 grain A-max bullet with an average muzzle velocity of 2684 from my rifle.  I used my FN PBR-XP with a pillar bedded McMillan A5 stock, Bartlein 20” Remington Varmint 1-10” twist barrel, and my usual SWFA SS 3-9×42 scope.  A Near base and Seekins rings provide the scope to receiver interface.


My target backer turned out to be 204 yards from my shooting position.  I tried for exactly 200 but had to settle for where I could put the backer and find a flat spot to shoot.  It was approximately 80 degrees and the density altitude was approximately 4500.  It was a calm day with a very little wind 1-2 mph coming from 5:30 to 6:00.  The FDAC and the iPhone ballistic program Shooter had a disagreement on the necessary elevation correction.  I usually use the iPhone and remembered it being a little off, so I went with the FDAC, and a 0.6 mil correction.

I shot all three ten shot groups in the span of approximately a half hour.  I was trying to give the barrel an opportunity to cool down to a reasonable temperature that would not induce any mirage, but I would have needed to wait longer.  I only had so much time to spend shooting.


I began to discover with the first ‘control’ group, that 30 seconds between shots is a long time.  It’s difficult to ride the correct balance between taking too long, keeping the barrel as constant in temperature as is reasonably possible, maintaining sufficient comfort to shoot one’s best, etc., etc…  It’s a decent time interval for a slow fire group.

Here is the resulting group:

9-8-14 Bipod Prone Slow

The time stress group in the photo below was evidently more comfortable for me in this position, as I shot a bit better.  The average split time between shots excluding loading or reloading, was 5.72 seconds, the high being 6.76 and the low 4.41.  The average split time of the entire testing of all the positions was 6.53 seconds.  I think that the split time is an indicator of how easy it is to acquire and maintain an acceptable sight picture in the position, as well as work the bolt.  This position is easy in both regards.

9-8-14 Bipod Prone Time Stress

With exertion added, my group degraded a bit as is expected.  I did 73 jumping jacks in a minute and it took approximately 23 seconds to get my 20 good pushups in.  I had a problem with the iPhone shot timer, in that it stopped recording times at shot #2.  My stopwatch indicated a total time that was approximately 7 seconds slower than the time stress without exertion added.

9-8-14 Bipod Prone TSE

After all the number crunching was done, pretty much all of it by computers, here are the distances I came up with.  I have two graphs.  As I explained in the previous article, I set one distance limit at 86% and another more stringent limit at 99%.  These represent the statistical predictions of distances at which 86% and 99% of my shots will land within the 4” target, assuming that I account for wind correctly and that my rifle is perfectly zeroed (a significant assumption- and the reason you see shots outside the black at a lesser distance).


Maximum Distance 86 Bipod Pronea


Maximum Distance 99 Bipod Pronea

Another thing that I’m keeping track of is how much the position degrades, if at all, as stressors are added.  That should give me an idea of whether it’s only useful for shooting static targets on the range when all is well, or if the position also works well in less than optimal situations.  I’m using the slow fire group as a baseline, and comparing the performance of the time stress and time stress exerted groups as percentages of that performance.  In this case the time stress group was better and actually added 115.74% effective distance.  The time stress exertion group gave me effectively 89.95% of the effective distance in comparison to the slow fire group.

This was the only position in which the shot group improved under any of the stressors.  The 10.05% degradation in group size under exertion was small in comparison to the amount that other positions suffered.  This is to be expected when the ground is doing more work than the shooter in supporting the rifle.  Surprisingly, this position did not yield the greatest precision.  You’ll just have to wait and see which position did.

Goal and Progress Evaluation

Exactly 11 months ago I set a goal with a deadline of May 1st, 2014. The last 10 months or so had me completely off track so I’m doing what I can to make good on my goal setting. The goal was stated as follows:

Develop the ability to hit an uncooperative moving target, no greater than 4” in diameter, inside of 200 yards at known or unknown distance, on demand, regardless of terrain, conditions, stress, tiredness, fatigue, or time constraints.

Even with being off track, there were some serious problems with my goal. First of all, it’s unrealistic. It sounds easy because of the 200 yard limitation, but if prone is not an option things can get dicey pretty quickly. Spend 30 minutes moving into a concealed position and set up a position on a target while remaining concealed. Experience tells me that prone will probably not be an option. Then a 2 MOA target is anything but easy.

Secondly, I might as well have set a goal that I wanted to make $500,000 in 2014, without really knowing what my current income was or how I might make that money. A reasonable goal for someone in my position in November of 2013 would have been simply to identify my baseline level of skill in reference to a larger goal and put a two month deadline on it.

Thirdly, there is a serious issue of how to measure performance in relation to the goal. How do I define things like ‘tiredness’ and ‘fatigue’ in measuring how I shoot under these conditions? What type of time constraints should I implement to induce stress for evaluation purposes? How can an uncooperative target be simulated in a way that is repeatable enough to form a meaningful prediction without becoming predictable?

The short answer is that it’s really not possible to know enough about a future situation to predict what will constitute successful performance in that situation. How many variables can a person possibly measure and try to keep track of, especially given the fleeting nature of time, ammunition, and sanity? The answer is not more than two. Okay, I just made that up.

If you know me at all, you’ve already realized that I couldn’t give up that easily at an opportunity to shoot excessive amounts of ammo, crunch numbers, and drive myself a little more crazy than I was yesterday. Really though, I felt that it was irresponsible to do all this practice and ostensible preparation without making some effort to have a way to predict how I might perform than simply taking aim at a target, trying my best, and hoping for a good outcome.


I spent the early part of the year enthralled in measuring things. From the mid part of the year on, my gears have shifted into analysis. I have to thank John Simpson for getting me started down this road and introducing me to a wider range of statistical measures. I also have to thank David Bookstaber of Ballistipedia for helping me figure out how to take my outputs from On Target and convert them into something that was both statistically valid and meaningful to me as a shooter.

I won’t turn this into an academic discussion on statistics, but I’ll give you the skinny on how I’m getting my numbers. I measure my targets with On Target TDS, which allows the measurements to exported on a .csv (comma separated values) spreadsheet. This spreadsheet can be imported into a free online program created by Daniel Wollschlaeger called ShotGroups. Shotgroups generates a lot of things that I don’t even begin to understand, but it also calculates an ‘unbiased’ mean radius which can be used to estimate the Circular Error Probable (CEP), which is the radius of a circle that would contain 50% of shots fired under identical conditions as the sample group. The figure can also be used to calculate radii of circles that would contain different percentages of a shot group, such as a 99% circle for example.

In my goal I did not state an acceptable percentage of hits. That implies that I think I could conceivably hit with every shot, which is not possible. I decided to use two different criteria to allow more flexibility depending on what I need for the situation, an 86% circle and a 99% circle. They are easy to calculate because they represent the standard deviation multiplied by 2 and 3 respectively.

The final step of turning a statistic into something that is meaningful to me as a shooter was to turn that predicted radius into a distance. Knowing that my target is a fixed size, 4”, it made it easy to state that, given a certain sample group, 99% of the shots should land within the target at “X” distance.

I identified nine likely positions that I might shoot from that would cover a variety of possible terrain. From each position I fired ten shots in three different conditions. The first group of ten shots was sort of a ‘control’, and allowed me a slow fire pace with an average of 30 seconds between shots. To accomplish this I simply set a timer on my watch for a repeating 30 seconds. I say ‘average’ because I did not initiate a ‘command’ break on the trigger, nor did I intentionally break a shot under what I felt was an unacceptable sight picture.

The second 10 shots were fired under simulated time stress. I started with an empty rifle, empty magazines, and a container of 10 rounds lying next to the magazines. I started a shot timer app (which I can’t recommend for serious use) and at the signal, loaded my magazines as quickly as possible and fired ten rounds at a single target as quickly as possible.

The third 10 shots were also fired under the same simulated time stress, but a component of exertion was added. I did one minute of jumping jacks followed by 20 pushups prior to setting the shot timer. This doesn’t represent any form of maximum exertion, simply a repeatable marker that will give me an idea how a given position might deteriorate with increased heart rate, respiration, and a very small amount of muscle fatigue.

The numbers I come up with are not intended to cover the gamut of possibilities of the interaction of human variables. They just give me a better idea than I had before. For example, if the statistics predict that under time stress and exertion, 99% of my shots from unsupported standing will be within my 4” target at a distance of 20 yards, how does that explain that my normal hit ratio working on speed drills with the AR from 7 yards was approximately 90%? The answer is that the conditions, methods, and expectations were different. I was pushing my speed to my edge and just beyond, and was trying to walk the fine balance of hits and speed. I expected some misses. The thing I measured with the AR was not the thing I measured in these tests, where hitting the target was the primary goal.

The positions I tested were bipod prone, supported sitting, supported reverse kneeling, two forms of supported standing, open leg sitting, cross ankle sitting, squatting, kneeling, and standing. Instead of being reasonably “in shape” as a shooter who is trying to accomplish a goal, I came off of a short break that followed my epic episode of number crunching, chart drawing, and writing about scopes and how they affected my performance. I was not in prime shape for me.

The rest of this month will detail my results in shooting from those positions, and what distances I might be able to predict with some confidence a hit on my well delineated, highly visible, extremely cooperative 4” target. I will keep it relatively short and sweet. It was an interesting process for me, and I hope you’ll like it too.