9 replies to this topic

[Khail]

Okay, after performing mods on a couple of my plunger guns, I was wondering about the connection between the plunger shaft and dart barrel. Is it better to keep the part where it tapers into a smaller tube, or just to connect the plunger tube and dart barrel together and bridge the gap with something?

[Spoon]

The tapering probably leads to less air turbulence and therefore higher pressure. As long as it is a relatively short length of tapering you should be fine.

[cxwq]

Agreed. The tapered section is probably not an issue as long as it's relatively low volume.

[GunnedDown]

If you do not lessen the airspace in the barrel, you will not achieve much range at all. This is what happened when I tried to single barrel my AT1k. I probably need to insert a few glue rings. It's one of the basic aerodynamic laws, I forget whose law it is though, I think it is Pascals.. Anyway, that smaller hole will allow the air to be pushed out with more force, to an extent. You can't have an uber-tiny pinhole or something, though, and expect the nerf dart to go far. You'd need to find a balance.

[Sacapuntas Cabesa]

I'm just pulling this equation out of my ass, and there are no coefficents, but just so you get the idea:

Strength of Plunger/Diameter of Hole = Speed of Air

A pinhole would create the fastest moving air, but only if the plunger was strong enough to force that huge volume of air in the plunger chamber through the tiny hole in the same amount of time. Also, the bigger the hole, the weaker your plunger can be. The Nerf people most likely figured out the best ratio for this.

[cxwq]

The velocity of the air stream is less important than the volume of air delivered. What you have to do to get the dart moving as quickly as possible is dump one barrel volume of air into the barrel in as short a time as possible. This is achieved by opening up all restrictions between the plunger and the barrel. The Nerf engineers calculated how much they needed to restrict it to make it safe.

[Zero Talent]

Yeah, I read somewhere that as a certain pressure of air is forced into a smaller opening, it's velocity increases, but the force it exerts is lower. Of course, I can't seem to find anything on Pressure Laws relating to Kinematics on Google, so I'm lost for visual aid.

[cxwq]

I agree with the physics you guys are talking about. I just think you're making it more complex than it is.

When you have a dart in a barrel, the 'jet of air' is not acting directly on the dart. The dart moves due to the pressure differential on either side of it. That's why we have a barrel in the first place.

The faster you can build high pressure behind the dart, the faster it will move. The higher a pressure you can achieve behind the dart before it leaves the barrel, the faster it will move.

So your challenge is to get as much air as possible into the barrel before the dart leaves the gun.

[Sacapuntas Cabesa]

Yes, but the speed of the air is still important in plunger guns. I don't know of any physics to prove this, but trial and error has shown that you should NOT drill out the hole between the barrel and the plunger tube. At least not very much. I killed a SSI this way, and had to do massive repairs on others.

[cxwq]

I'm interested to hear details of these experiments.

I can see the possible advantage of airway restriction in plunger guns where there simply isn't enough volume in the plunger to adequately pressurize the entire barrel or where the dart is not a tight fit. What type(s) of barrel/dart did you experience this with? Barrel length?