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.

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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.

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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).

86%:

Maximum Distance 86 Bipod Pronea

99%

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.

8 thoughts on “Bipod Prone Analysis

  1. Your article was well written and I enjoyed reading it. I reload, and sometimes I get a little too technical for most people. And, God forgive me, but I can’t help but think that at 200 yards I could likely drill you center body mass with the po little ol .275 Rigby I just finished building before you could get your gloves rolled up! I have been shooting for 45 yrs. Having gotten older, I find myself more interested in the functional rather than the perfect. I got Williams Apature sights on that old rebuilt Oviedo Spanish 7X57, with a good new Barrel. Put a nice Boyd’s Stock on it-it was a wintertime project. We are two sides of the same coin, which is what makes Rifle so very interesting. Hunt Coyotes—they are an education!!! And may God bless us both!

    • It must not have been too well written if your first thought was to drill me with your 7×57 😐

      For what it’s worth, I keep my gloves already rolled up. It’s that right side backpack pocket you have to watch for 😉

      I ask only that you not take a gut shot.

      Cheers and God bless you.

        • I have a lot of fun on the “Range”,and go there to work on my “handloads” for a variety of Rifles and pistols—But I hunt Deer and Trap,Call, and hunt predators here also. Usually this is in very thick cover typical of the area. Many shots are taken offhand and quickly. BUT-when things are are a little more open–you can drop to that sitting position pretty darn quick.

          • Dropping from standing ready to a good sitting position and getting the hit with the first shot is probably the skill I treasure the most.

  2. Once you get all the stars and planets in perfect alignment, then you can get back to that old devil rifle bounce.

    • Pete,

      I feel like actually having some concrete data on my shooting is a breakthrough in how I approach my training as a shooter. These tests also mark the first time in a while that I’ve done anything other than prone with the bolt action, which I think of as the beginning of my return to the real nuts and bolts.

      I think that the Rifle Bounce and Rifle Ten are both fun and useful as drills and training tools. Where I think they are lacking is as diagnostics. They are pretty involved, and the performance from one rep to another can be pretty highly variable, so I think that it would take enough reps at any given drill to be able to see trends rather than individual data points.

      This series of tests has really shown me a lot about what each position is best for, where it excels, and what its limitations are. I really feel like knowing this will help me be more fluid and dynamic in application.

      I think that the next step in gaining some practical knowledge on my shooting is to figure out what my time is from a carry position to a hit on target.

      I was hopeful when I did the Cooper drills way back when that some people would join me and we could get an informal competition, or at least a score database going. It didn’t really catch on, which was disappointing. There is one fellow working at the Whelen Challenge though, which is nice to see: http://www.scoutrifle.org/index.php?topic=4541.0

      My positional shooting has gotten a little rusty. I was happy to see that even with my lack of recent practice, I was a little better in most cases than my attempts back in 2011 (and I really trained up before shooting groups for the blog back then).

      I’m glad you’re still reading. Feed Mongo some biscuit and mustard for me.

      • Pete reads, Mongo looks at the pictures. Mongo like mustard and biscuit, also like mustard and mice, mustard and racoons, and mustard and cats. Even mustard and mustard. Mongo no like mustard and skunk.

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