I have always been fascinated with the mechanics of different types of guns, and since the impulse test was Tuesday, it is a good time to look at one of the more common questions surrounding "explosion" type collisions. One of the most powerful weapons is the Barrett .50 Caliber Sniper Rifle. Although there are multiple types of bullets used, an armor piercing bullet for a .50 cal is around 45.8 grams (just the projected portion), which is .0458kg. The bullet leaves the barrel of the rifle at speeds of roughly 856 m/s. This means the momentum in the forward direction is 39.2 J, which means that the momentum of the recoil of the rifle is 39.2 J as well. Since the rifle is often against the shooter's shoulder (some .50 cals have remote control shooting), the impulse felt by the shooter is 39.2 J as the rifle slows to a stop in a fraction of a second. To compensate for the large impulse during a short time, creating a very large force on the shooter's shoulder, the .50 Cal Sniper Rifle has a built in recoil pad in order to increase the time that the momentum is changing, therefore decreasing the force felt by the shooter.

Another important part of shooting a .50 cal is accuracy since the weapon was designed to take out large targets from far away. In order to maintain a straight flight in the air, like all guns, the barrel has grooves so that the bullet starts spinning while being projected by the gun, keeping it stable during flight. Also, since the velocity of bullet as it is leaving the barrel is 856 m/s, without counting for air resistance or air pressure, the bullet would travel 856 meters in 1 second, and during that second the bullet would only fall 4.9 meters vertically. Since 858 meters is half of a mile, that is a very small vertical displacement. More importantly when shooting long ranges like this, the shooter must take into account wind conditions, humidity and air pressure (and their own breathing). Although it may seem that these small factors would not affect a small bullet traveling at 800+ meters per second, over the course of half a mile to a mile, even the smallest anomolies could be the difference between hitting the target and missing wide or high. Luckily, most snipers of this power have scopes that can calibrate the crosshairs based off the input of the air conditions and wind since accounting for these conditions with the human eye is virtually impossible. Taking into account these conditions is especially important since the maximum effective range of a .50 cal sniper is 1800 meters. For example, if a person aims .05 degrees (yes, that is .05) away from where they need to aim due to the conditions, the shot would miss by about 1.5 meters in the direction their error was in which could be the difference between hitting a target or missing it completely. 

Good thing only the best in the US military are trusted to use such powerful and precise weapons, especially since the cost of each one is over $10,000. 

The sniper looked at during this post was a military M107 .50 Caliber Sniper Rifle (aka M82). The .50 caliber is the diameter of the bullet (.5 of an inch), while this uses BMG (Browning Machine Gun) bullets which is the most powerful type of .50 cal bullets.