Special thanks to Aki Katsabas, Jody Kirtland, John Epley, and Charles Dean for their help with this project.
In various forms, the following claim has been made numerous times in web forums, such as PBNation.com, and in a recent Planet Eclipse commercial featuring professional paintball player Oliver Lang:
The poppet-based Planet Eclipse Ego line of markers has a drop shot, i.e. a more sharply downward arching trajectory, compared to the spool-based Geo line of markers.
If this is true, paintballs fired from an LV1 will strike at an increasingly lower point on a target than will paintballs fired from a Geo 3.1 as the target moves farther away. All projectiles follow a curved flight path as the forces of gravity and drag act to return them to rest on the earth. Without taking into account drag, the trajectory can be defined as a parabola. With drag added in, a projectile is seen to increasingly lose forward velocity over time, thus speeding it faster towards the earth. In other words, a paintball’s trajectory is expected to be flatter at the beginning of its flight, then curve more and more toward the earth at the end of its flight. This is true of every paintball marker. But what some people have claimed about the Ego line of markers is that paintballs actually drop more precipitously than expected, creating a “drop shot” effect that some consider advantageous for eliminating opponents behind certain low obstacles, such as “snake beams” or “Doritos”.
Ballistics teaches us that the only force that could cause this type of exaggerated downward arch is the Magnus force (or possibly the reverse, or anti-, Magnus force), caused by a top (or bottom) spin imparted to the paintball. One would generally expect such a spin to be caused by some force applied to the ball perpendicular to the intended flight path: whether it be drag applied to the shell of an asymmetric paintball; poor paintball-to-barrel bore match allowing high-velocity air inside the barrel to race over the top of the ball; friction caused by scuffing along the inside of the barrel; or asymmetric, possibly turbulent, exhaust flow from the bolt pushing more on the top or bottom of the ball. Unfortunately, without strobes and high-speed cameras, we are unable to see if flying paintballs attain sufficient spin to experience the Magnus effect. Nevertheless, as long as we control for paint, velocity, environmental, and barrel conditions, we should be able to prove whether or not the “Ego drop-shot” is true or not simply by observing whether paintballs fired from an Ego LV1 strike lower from the bore line than those fired from a Geo 3.1 on a target that continuously gets farther from the muzzles. (It is important to note that this would be a relative comparison between two markers, not an absolute measure of shot drop.)
Experiment 1 was conducted on March 31, 2014, at an outdoor paintball field. The test used a plastic table and commercially available hunting rifle vice for a shooting stand, a plastic table top and poster board for a target, and a laser bore site to verify zero. Some of the principle problems we faced with this set-up were that the plastic shooting table had some flex in it, the gun vice did not have the strongest grip on the marker, and the ground was more uneven than anticipated. Another problem was a 12-14 mph crosswind. Nevertheless, we decided to proceed with the experiment, if only to satisfy our own curiosity.
EXPERIMENT 1 RESULTS
Surprisingly, the results of our crude, initial test did in fact appear to validate the claim of an LV1 drop shot. But since there was every reason to be skeptical of the results, instead of going public I decided to share our findings with Planet Eclipse in hopes of soliciting some expert advice. Doing so led to an interesting and motivating email exchange with Jack Wood of Planet Eclipse. Jack expressed an interest in seeing the experiment conducted again, but under more rigorous controls. We needed a better gun vice, target, laser and level, and we needed to take the whole thing in-doors. Jack also wanted more shots per gun at each distance and three data points per shot: distance, elevation drop, and velocity.
I secured access to an indoor facility, where cross winds would not be an issue, and built an improved vice and target. After several weeks of preparation, we conducted Round2 of testing. These are the results of that test.
1. Dyrkacz, Gary, The Physics of Paintball; http://lennon.csufresno.edu/~nas31/nsa/physics.html
2. Davies, J.M., The Aerodynamics of Golf Balls; J. Applied Physics, 20, 821-828 (1949)
III. EXPERIMENT DESIGN
1. Obtain a Planet Eclipse Ego LV1 and a Planet Eclipse Geo 3.1.
2. Use the same, brand new Shaft 4 barrel kit for both guns.
3. Use fresh, good quality paintballs from the same bag.
4. Using a handheld chronograph, set the velocity of each marker as close to 280 fps as possible.
5. Set up a table and gun vice as a shooting station. The shooting station does not move.
6. Use a sheet of durable material to create a target and mount it on a stand that can be adjusted for elevation. Draw a “zero line” near the top of the target, then mark every inch going down from the zero line to the bottom of the target board. At the center of the zero line, place an orange mark. The target can then be raised or lowered relative to the table top in order to adjust for ground elevation changes, thus allowing the zero line to always remain level to the muzzle line.
7. Place the LV1 securely in the gun vice, and clamp the vice to a work bench.
8. Mount a small bubble level and a laser sight with a remote switch to the barrel, making sure not to obstruct any of the barrel ports.
9. Set the target at its starting distance of 10-feet from the tip of the muzzle.
10. Use the bubble level to level the marker in the vice. Turn on the laser sight. Adjust the height of the target using its telescoping stand until the laser points precisely at the orange dot on the zero line of the target. This provides us with a straight, level bore line, or zero height.
11. Fire 20 shots from the marker and record each shot’s velocity and elevation drop relative to the zero line.
12. Move the target 10-feet farther from the muzzle and repeat the process of laser zeroing, test firing, and recording elevation drop until reaching a final distance of 90-feet from muzzle to target. Do not move the marker or change any settings during testing.
13. Replace the LV1 with the Geo 3.1, reset the target back to 10-feet, and repeat steps 8-12 to test the shot drop of the Geo 3.1.
EXPERIMENT 2 RESULTS
In Experiment 2, we observed no significant difference between the trajectories of the LV1 and the Geo 3.1.
Link to raw data spreadsheet: https://drive.google.com/file/d/0ByH...it?usp=sharing
TIME, WEATHER, and LOCATION
Date: April 27, 2014
Time: 1:00 PM – 7:00 PM
MAX 89°F (31.6667°C)
MIN 75°F (23.8889°C)
AVERAGE 82°F (27.7778°C)
Private Warehouse in Cypress, TX, USA (Northwest Houston)
MARKERS, PAINTBALLS, and BARREL
Dwell: 16.8 ms
LPR: 80 psi (verified with Violent Products LPR gauge)
Solenoid: Restrictor A = 5; Restrictor B = 7
Average Velocity: 267.911 fps
Dwell: 26.2 ms
Solenoid Flow Restrictor: ~50% flow
Average Velocity: 275.761 fps
14” Planet Eclipse Shaft 4 with 0.689 back