The Improved Pen Gun
Posted: Tue May 13, 2008 11:12 am
rcman50166's Pen Gun
First I want to say that this is not to show up JSR's pen gun. As a matter of fact, if it wasn't for him building it I probably never would have.
Improvements
JSR's pen gun was good but there were several things I saw that could be improved. The first was the piston. My pen gun has a smaller, lighter piston made from a small nylon spacer. The inside of the spacer was injected with hot glue and then shaped to make the barrel seal. This brings me to the second improvement. JSR's pen gun had the seal attached to a barrel bracket. This restricts air flow from the chamber to the barrel, potentially lowering efficiency. My pen gun has no such bracket so when the piston is in its exhaust position there is nothing blocking the chamber to the barrel, allowing for maximum efficiency. This again leads to the next improvement. JSR's pen gun has epoxy (I think) sealing the foreward end of the gun. Mine uses an o ring partnered with the top of a pen to seal the front which also stablizes the barrel allowing for no bracket on the other end as mentioned before. The pen is shortened to simulate the length of a regular disposable pen. The shrader valve is also vented by the pen cap which has a rod in it which looks like a click button.
Features
The barrel is at the same diameter as a pen's ink tube which, convieniently, is also the diameter of my ammo. It shoots pencilt tips. This is ideal because you can sharpen the tips and even rifle the round. Graphite also is known as a dry lubricant so as you shoot the pen, the round lubricates the barrel for the next shot. All together the pen gun costs $6.
Downsides
The downside of my particular design is that unless lubricated periodically, the valve may stick. Also, since there is no bracket to stablize the barrel, the barrel doesn't always line up with the seal. I personally fixed the problem on my pen gun. But the problem will be unique to every one built. Another potential problem, depending on the power desired, making the gun shorter makes the chamber and barrel shorter, a problem that can plaugue a pneumatic if extreme enough. However, I'm happy with it's performance overall.
Performance
Once all the kinks were worked out, my pen gun became very reliable, only requiring lubrication about every 100 shots. It has been tested with a small ball/bike hand pump, which I would guess to be around 50PSIG. I plan to test it at 250 PSIG this weekend. At 50PSIG (with the small pump), I was able to shoot through two pieces of paper even while the round tumbled into it sideways. I can shoot through one layer of a small plastic sandwich bag. It is plenty accurate only straying off with light ammo. However, the piston tended to stick when orange peels were loaded in. There are no apparant leaks when it is put through its paces in the underwater test. It can make someone bleed. I brought it to school to test its undercover capabilities and no one recognized it as a weapon, only the occasional "cool gold pen".
[youtube][/youtube]
Click here to see jackssmirkingrevenge's pen gun.
First I want to say that this is not to show up JSR's pen gun. As a matter of fact, if it wasn't for him building it I probably never would have.
Improvements
JSR's pen gun was good but there were several things I saw that could be improved. The first was the piston. My pen gun has a smaller, lighter piston made from a small nylon spacer. The inside of the spacer was injected with hot glue and then shaped to make the barrel seal. This brings me to the second improvement. JSR's pen gun had the seal attached to a barrel bracket. This restricts air flow from the chamber to the barrel, potentially lowering efficiency. My pen gun has no such bracket so when the piston is in its exhaust position there is nothing blocking the chamber to the barrel, allowing for maximum efficiency. This again leads to the next improvement. JSR's pen gun has epoxy (I think) sealing the foreward end of the gun. Mine uses an o ring partnered with the top of a pen to seal the front which also stablizes the barrel allowing for no bracket on the other end as mentioned before. The pen is shortened to simulate the length of a regular disposable pen. The shrader valve is also vented by the pen cap which has a rod in it which looks like a click button.
Features
The barrel is at the same diameter as a pen's ink tube which, convieniently, is also the diameter of my ammo. It shoots pencilt tips. This is ideal because you can sharpen the tips and even rifle the round. Graphite also is known as a dry lubricant so as you shoot the pen, the round lubricates the barrel for the next shot. All together the pen gun costs $6.
Downsides
The downside of my particular design is that unless lubricated periodically, the valve may stick. Also, since there is no bracket to stablize the barrel, the barrel doesn't always line up with the seal. I personally fixed the problem on my pen gun. But the problem will be unique to every one built. Another potential problem, depending on the power desired, making the gun shorter makes the chamber and barrel shorter, a problem that can plaugue a pneumatic if extreme enough. However, I'm happy with it's performance overall.
Performance
Once all the kinks were worked out, my pen gun became very reliable, only requiring lubrication about every 100 shots. It has been tested with a small ball/bike hand pump, which I would guess to be around 50PSIG. I plan to test it at 250 PSIG this weekend. At 50PSIG (with the small pump), I was able to shoot through two pieces of paper even while the round tumbled into it sideways. I can shoot through one layer of a small plastic sandwich bag. It is plenty accurate only straying off with light ammo. However, the piston tended to stick when orange peels were loaded in. There are no apparant leaks when it is put through its paces in the underwater test. It can make someone bleed. I brought it to school to test its undercover capabilities and no one recognized it as a weapon, only the occasional "cool gold pen".
[youtube][/youtube]
Click here to see jackssmirkingrevenge's pen gun.
