By Will Dabbs, MD, American Handgunner
Photos: Sarah Dabbs
The fourth cardinal safety rule of shooting is not to touch the trigger unless you’re certain of your backstop and what is beyond it. For this reason it’s seldom a good idea to shoot into water. At shallow angles, bullets typically glance off to follow an unpredictable path. Bullets bounce quite a lot regardless of the backstop.
I was once on a night patrol well downrange from a machinegun range back when I wore the uniform. In the distance tracers arced up into the heavens in a gorgeous display of pyrotechnics. While I was stretched out in the prone I felt something thump into the dirt near my hand. Feeling around with my fingers I retrieved a sizzling 7.62x51mm ball projectile which fell mere inches from my head. I quietly suggested to the patrol leader we find a better spot for our patrol base.
The physical science behind the ricochet is fascinating. Bullets are like little batteries. You charge them up with a quantity of energy and they expend that energy on targets downrange. In the case of water, liquids are incompressible and can facilitate a collision where the bullet still retains a dangerous amount of energy. There seems to be a critical angle of incidence determining whether a bullet dives down into the water or bounces off into the stratosphere. This phenomenon is based upon countless factors, some of which are entirely unpredictable.
I once attended a machinegun shoot in Alaska overlooking an enormous lake. In this unique environment the downrange area was cleared and the backstop was the Alaskan mountain range some 50 miles away. One of the coolest things I did was fire bursts from my 9mm MAC10 across the water. The bullets would strike the surface of the lake and then glance off to the right about ten degrees with each subsequent impact due to the bullet’s rotation. The lake was large enough to get two or three skips, each taking the bullets farther to the right. The effect at 1,200 rounds per minute was fairly sublime.
When the angles are perfect a bullet will skip like a stone. Therein lies the danger. Once a rounds glances off of water, its trajectory becomes erratic and unpredictable.
When the backstop is safe there is little more fun than a machinegun, a Holosight, a Betamag and a wet target. Sadly, the circumstances under
which this can be safely undertaken are fairly narrow.
Our Test Range
The range area used for this testing is fairly unique. It overlooks a lake surrounded like an amphitheater by a 60′ semicircular ridge covered with old-growth trees. It’s one of the very few shooting spaces I’ve seen where it’s legitimately safe to shoot into the water. With this as a laboratory I undertook a little junk science to investigate the nature of the ricochet. This undertaking was not rigorous nor did it bear any of the true hallmarks of good science. I just wanted to answer some simple questions, not produce the seminal work on the subject.
I secured a big blue tarp between two trees at the water’s edge and then measured the distance from my shooting point to the point of impact on the lake and then on to the target beyond. I measured the height above the water of the weapons fired, and then the subsequent height of the holes in the tarp. With a little help from my mathematician bride, I then calculated the angle at which each bullet struck the water and then the subsequent angle of reflection after it skipped off. I would like to have determined velocities after impact with the water but was unable to divine a way to do this without blowing my chronograph to smithereens or drowning it in the lake.
I used a single fixed geometry and repeated my testing with four different calibers — .22 LR, 9mm, .45 ACP and .223. I then varied the angle of incidence to the water using both 9mm and .223 to see the point at which the bullets began to bounce rather than dive into the water. The results are included in the attached tables and were thought provoking, if not particularly practical.
Though it bore little semblance to actual rigorous science, these were the tools we used on our undertaking to investigate the physics behind the ricochet. The results were interesting — if not terribly practical.
We repeated our testing with four different firearms: .22 LR, 9mm, .45 ACP and .223. All had their own unique personalities downrange.
The .22 LR, 9mm and .45 ACP FMJ rounds skipped consistently and predictably. I actually produced a couple of quasi-decent groups on my tarp with these calibers. The .223, however, was radically random. These unstable high-velocity bullets struck the tarp sideways as well as point on and the reflected angles, even from the same initial geometry, varied widely. Some were sufficient to miss the tarp altogether so the reported geometry for the .223 is a rough estimate at best.
The bottom line is there is an awful lot of random going into these equations, particularly with high-velocity rifle rounds. As a result, it’s indeed only within a very narrow set of circumstances where I’d call it is safe to shoot into any body of water. In my case I only do so because of this prodigious natural backstop.
Guns are great fun but they are inherently dangerous tools, notoriously intolerant of inattention or stupidity. What I found after a day of trying to bounce bullets into a tarpaulin under controlled circumstances is the subsequent flight of a ricocheted projectile is innately erratic and unpredictable. If the angle is fairly sharp, the bullet frequently just dives into the water, but even on dirt bullets can bounce in an alarming fashion.
Always remember the fourth cardinal rule of shooting: Before you pull the trigger, be absolutely certain of the target and the area beyond. Be careful and be safe.
|Caliber||Angle of Incidence||Average Angle of Reflection|
|.22 LR||2.5 deg||5.6 deg|
|9mm FM||2.5 deg||9.5 deg|
|.45 ACP FMJ||2.5 deg||8 deg|
|.223||2.5 deg||16 deg|
*Test guns were fired 76” above the water to a point of impact on
the water 144 feet distant. Subsequent target was 12 feet beyond
the point of impact with the water.
Reflected Angles at Various Angles of Incidence
|Angle of Incidence||Angle of Reflection||Angle of Incidence||Angle of Reflection|
|24 deg||No Ricochet||24 deg||No Ricochet|
|12.5 deg||No Ricochet||12.5 deg||9.5 deg|
|8.5 deg||9.5 deg||8.5 deg||14 deg|
|5 deg||12 deg||5 deg||26 deg|
Thanks to the team at American Handgunner for this post. To visit Handgunner – click here. To check out subscription options and get Handgunner delivered to your door – click here.