Actually, my nerf gun wasn't modified. This conversion was more of an attachment than a modification. (I did, though, modify the nerf gun to shoot farther. Standard air restrictor removal and penny spring mod. Shoots 50 feet with streamline darts).
Here's how it works.
I took a nerf dart and cut off the head. Now it's a nerf tube.
I took a steel airsoft barrel from an airsoft tank that I took apart quite some time ago and
1. Attached a circuit hook-up wire across one end with masking tape
and
2. Put a small line of masking tape on the inside on the same end of the barrel, making a full circle. (you can see it a bit inside the barrel here)
I stuffed the steel barrel into the nerf tube and the modification is now complete.
The small wire on the barrel end serves to keep the BB in the barrel when aiming and loading (muzzle-loaded), so it doesn't fall out the end into the nerf gun itself.
The small lining of tape serves to hold the BB in the barrel when loaded, so it doesn't slide out when the gun points down.
By simply stuffing the above modified dart into the barrel of the nerf gun, the nerf gun was thus converted into an airsoft gun.
Using a simple setup with a stool, measuring tape, a laser pointer, and a shopping bag, I used kinematics to find that the crude approximate speed of the gun is around 277.788714 fps (feet per second). This is using 0.12g low-end BB's. If a 0.20g standard BB was used, the speed would have theoretically been (using conservation of energy) around 215.174213 fps. Which is pretty close to some mid-to-high-end spring-powered airsoft guns. Dang.
What I did was put the gun on the stool and made sure it was level by eye. I used the laser pointer to line up the gun with a paper shopping bag 10 ft away. By firing the gun and finding the height difference from launch to bag puncture, I could find
1. the time it took to get there.
2. using the time found, calculate the speed it had over 10 ft.
Which came out to the wonderful number you see above.
When I have more time, I'm going to make a better setup for better speed calculation - using bubble levels and a stiffer bag for better measurement.
