Over-Shooting the Berm — When a Mere 5 Degrees Can Be Deadly
In our Shooters’ Forum, there was an discussion about a range that was threatened with closure because rifle over-shoots were hitting a farm building over two miles from the firing line. One reader was skeptical of this, asking “how’s that possible — were these guys aiming at the stars?” Actually, you may be surprised. It doesn’t take much up-angle on a rifle to have a bullet land miles down-range. That’s why it’s so important that hunters and target shooters always orient their barrels in a safe direction (and angle). Shooters may not realize how much a small tilt of the barrel (above horizontal) can alter a bullet’s trajectory.
How many degrees of muzzle elevation do you think it would take to hit a barn at 3000 yards? Ten Degrees? Twenty Degrees? Actually the answer is much less — for a typical hunting cartridge, five to seven degrees of up-angle on the rifle is enough to create a trajectory that will have your bullet impacting at 3000 yards — that’s 1.7 miles away!
Five degrees isn’t much at all. Look at the diagram below. The angle actually displayed for the up-tilted rifle is a true 5.07 degrees (above horizontal). Using JBM Ballistics, we calculated 5.07° as the angle that would produce a 3000-yard impact with a 185gr .30-caliber bullet launched at 2850 fps MV. That would be a moderate “book load” for a .300 Win Mag deer rifle.
Here’s how we derived the angle value. Using Litz-derived BCs for a 185gr Berger Hunting VLD launched at 2850 fps, the drop at 3000 yards is 304.1 MOA (Minutes of Angle), assuming a 100-yard zero. This was calculated using a G7 BC with the JBM Ballistics Program. There are 60 MOA for each 1 degree of Angle. Thus, 304.1 MOA equals 5.068 degrees. So, that means that if you tilt up your muzzle just slightly over five degrees, your 185gr bullet (2850 fps MV) will impact 3000 yards down-range.
Figuring Trajectories with Different Bullets and MVs
If the bullet travels slower, or if you shoot a bullet with a lower BC, the angle elevation required for a 3000-yard impact goes up, but the principle is the same. Let’s say you have a 168gr HPBT MatchKing launched at 2750 fps MV from a .308 Winchester. (That’s a typical tactical load.) With a 100-yard zero, the total drop is 440.1 MOA, or 7.335 degrees. That’s more up-tilt than our example above, but seven degrees is still not that much, when you consider how a rifle might be handled during a negligent discharge. Think about a hunter getting into position for a prone shot. If careless, he could easily touch off the trigger with a muzzle up-angle of 10 degrees or more. Even when shooting from the bench, there is the possibility of discharging a rifle before the gun is leveled, sending the shot over the berm and, potentially, thousands of yards down-range.
Hopefully this article has shown folks that a very small amount of barrel elevation can make a huge difference in your bullet’s trajectory, and where it eventually lands. Nobody wants to put holes in a distant neighbor’s house, or worse yet, have the shot cause injury. Let’s go back to our original example of a 185gr bullet with a MV of 2850 fps. According to JBM, this projectile will still be traveling 687 fps at 3000 yards, with 193.7 ft/lbs of retained energy at that distance. That’s more than enough energy to be deadly.
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Tags: Berm, G7 BC, JBM Ballistics, Muzzle, safety, Trajectory
It gets a lot more complicated than that. Most civilian ranges are in similar jepoardy as they do not have the distance or terrain to capture errant shots or normal ricochets from the bullet skipping when it hits the ground.
The documented max ricochet distance for the 175 SMK out of a 308 is 5288 meters. That is distance X on for the 118 special ball on all military ranges.
The PA legislature funded a study several years ago that documented that a muzzle loading plastic tip bullet and the same type sabot in a shotgun actually had further ricochets than a 30’06 SP rifle bullet.
This was due to plastic tip protecting the projectile profile and reducing damage while the SP bullet was damaged and traveled less than the shot gun or muzzleloading bullets.
At 1000 yards, 5 degrees would be the same as aiming 262 feet over the target. That would be noticeable to most of us while aiming. The real issue is unaimed or accidental shots. Protecting from those requires more effort, but some mitigation can come from enforcing policies regarding closing the bolt only when the rifle is aimed at the target, and keeping fingers off of triggers until ready to fire.
For competitive shooting, I think the biggest risk is a slam fire in prone, where the rifle is elevated about 30 degrees and aimed 30 or 40 degrees to the left (right handed shooter).
5+ degrees is easy with an autoloader. When I was trying to determine the accuracy of my first autoloading rifle, I placed the rifle on a benchrest (fairly close to its balancing point to minimize upload on the barrel) and held it loosely (not in free recoil). I gently squeezed the trigger. The recoil was enough to raise the barrel, allow the butstock to bounce off my shoulder and “bump fire” a second round.
I am sure that I am not the only one who has had this happen.
Moral: make sure that the muzzle is held down, either manually or by some other means and be prepared for the potential of a recoil-induced bump fire.
Ministry of Defence qualified Range Conducting Officers in the UK are informed that the extreme range of a 7.62 x 51 mm NATO is 4000 m at a quadrant elevation of 600 mil (4375 yds at 34 degrees). For .308 long range match ammunition this could be up to 4500 m (almost 5000 yds). Bullets could richochet beyond this.
Hence the instruction to shooters (in the safety brief)”when loading, unloading, proving clear or dealing with a malfunction or missfire the rifle MUST be held horizontal and along your lane (so that any inadvertant shot will hit the butt stop” (berm)).
Loading, etc refers to locking the breech on a chambered live round.
34 degress is close to the angle adopted by Target Rifle Shooters (High Power?) between shots when trussed into a sling (I’ve been there!).