A friend and I were talking about picking up paintball as a hobby. We got to talking about it and we got the idea of Musket Paintball for two main reasons. One, we didn't have money. Two, we thought it would be more challenging to modify the rules of paintball a bit.

The core of the idea is to make your own paintball gun for cheap. We also didn't want to be spending money on refilling CO2 canisters. Again with the cheap.

The first part of this instructable is how to build a spud gun style paintball musket. If you're familiar with a spud gun or have already built one, this will be simple for you. There are only a few simple changes to make for paintball.

We did try compressed air but it didn't have the range we wanted. However we were only trying at +/- 100 psi. Some portable compressors say they can go to 300 psi which might work much better.

This isn't an absolutely unique idea obviously. There are others that have done similar projects.
https://www.instructables.com/id/Areosol-powered-paintball-gun-in-action/
https://www.instructables.com/id/paintball-air-cannon/
https://www.instructables.com/id/homemade-paintball-gun/

The main idea is to convey how to and then introduce the idea of a different class of paintball contest.

Step 1: Materials

The main idea here is to make a spud gun that will take a paintball. The design of this gun is to make loading the paintball and propellent easier.

These are the parts that have important dimensions.

3/4 inch CPVC pipe <- this is the barrel
2 inch PVC pipe <- this is the combustion chamber
1 1/2 inch cleanout adaptor
1 1/2 inch threaded adaptor to screw into the cleanout
2 inch end cap

The other parts that are variable based on availability. This is what I used.
1/2 inch to 3/4 inch adaptor
3/4 inch to 1 1/4 inch adaptor
1 1/4 inch to 1 1/2 inch threaded adaptor <- this is an odd part and may not be available

Other important parts
pushbutton grill lighter
2 short (1-1 1/2 inch) screws
PVC cement
Paintballs

Tools
Saw for cutting PVC
A drill
A screwdriver that works with your screws

Step 2: Cut Your Pipes

You only need 16 to 18 inches of 2 inch pipe for the combustion chamber. The barrel can be long for better effective range, but the CPVC will bend if it's over 3 foot long and that will make the gun inaccurate, defeating the purpose of a longer barrel. I chose to cut mine to approximately 20 inches. You could brace the CPVC and make the barrel longer. The main idea is that the barrel has to be straight to shoot straight.

Nearly any wood or metal saw will cut PVC. Here I'm using a hacksaw because it was in my basement when I decided to do this.

I haven't played around with making the combustion chamber smaller to see what the minimum size would be. Early on I tried a few that were way too small. If I find a minimum, I'll update this. A small chamber would be nice for portability. Larger chambers are more reliable because it's easier to get a good air to fuel ratio.

Step 3: Start Gluing

Using PVC solvent cement, glue two assemblies together.

First assembly
The 1/2 to 3/4 adaptor to the 3/4 to 1 1/4 adaptor to the 1 1/4 to 1 1/2 thread

Second assembly
The 1 1/2 threaded cleanout to the 1 1/2 to 2 inch adaptor to the 2 inch pipe.

Do not glue on the endcap! There are two reasons for this. One, it will make seeing into the combustion chamber easier for mounting the grill lighter. Two, it will serve as a pressure safety release so your paintballs don't leave massive welts on people.

Step 4: Attach the Grill Lighter

There are several ways to do this. It all depends on your screws. You want the screws to enter the combustion chamber and come within 1/16th of each other. The best way to do this is to have two screws that come in from either side of the pipe and almost touch. I didn't have the exact size screws so I opted to have them come into the pipe at angles so that they formed a V.

I drilled two holes roughly an inch apart angling in towards each other. The easiest way to get a good angle is to simply drill straight down into the pipe for the first hole, then rotate the pipe one inch and drill straight down again. You may have to adjust this based on the length of your screws.

I attached the leads to the grill lighter and then cut them to a manageable length (okay I could have cut them much shorter). Strip the wires back about a half inch.

insert the screws into the pipe and screw them in until there is just a small gap between the head of the screw and the pipe. Wrap the wires around the screw and tighten down.

I wrap my screws in electrical tape to prevent myself from getting an annoying shock by accidentally touching them while firing. It hurts.

Step 5: Glue in the Barrel

CPVC doesn't member up with PVC. The 3/4 inch CPVC nearly fits into the 1/2" PVC end of assembly 1. To get them to fit you'll need to file down the end of the CPVC pipe slightly.

Apply your PVC glue to the CPVC pipe and then force assembly 1 onto the pipe. I smacked it against the ground a couple times to get it to fit. Alternatively you could use a rubber mallet.

Step 6: Put It Together

Now simply screw the two parts together. Don't tighten them! You need to be able to unscrew them by hand.

Step 7: Load It and Test Fire!

To load the gun, unscrew the two halves and push a paintball into the breach of the barrel. The fit should be snug.

In the combustion chamber, spray some cheap aerosol spray like hairspray. You don't need a lot! just a small spray usually works. It will probably take a little bit of practice to get the right amount.

Screw the halves back together, point at something that you can make a mess on and pull the trigger.

If it doesn't fire, try adding some more spray and try again. Be careful not to spray in too much. The small combustion chamber can pretty easily get too rich a fuel mixture to combust. Having holes on both ends of the combustion chamber helps to clear it out when that happens.

When you fire, don't block the 2 inch end cap. It's function is to blow out if you've added too much propellant. This is a safety feature. The first few times I fired, the end cap flew off thirty feet!

The range of the launcher as shown is over 100 ft. The paintball will continue to fly another hundred but may not have enough force to burst. Last night we fired off a round that I'm pretty sure would have burst at 300 ft but that was with the pressure relief cap blocked and I wouldn't have wanted to have been in it's way.

Step 8: Musket Paintball Rules

The spud gun design is just an example. The principle of the design is a gun that can only launch one paintball at a time, like a musket. Guns that fire multiple charges of paintballs are not allowed! However loading several paintballs in the barrel and then firing is allowed as it acts like scattershot. The loading of the gun can be from the muzzle or the breach. Compressed air is a valid propellant if you can get it to work better than I did. The core of the game is to have to be careful with your shots. Instead of spraying the forest with paintballs and running, the name of the game here is careful aim.

You must wear all the safety gear you would normally during paintball. Despite the blow out cap, the paintballs can deliver a painful welt. Make sure to wear a face shield and any other protective gear.

With the variable strength of the guns, it is important to not try to hit the other players harder than is necessary to burst the paintball. Any player that causes a wound by breaking skin is disqualified.

Step 9: Variants

Build Variant
One variant to the combustion chamber would be to put in a T in and have the pressure release cap point down instead of backward. The tendency is to put the back of the musket up to the shoulder and that blocks the cap.

Rules Variant
Paintball Duel. Two contestants face back to back. One referee calls out the instructions and makes sure things are done properly. The contestants take ten paces, each step is called out by the referee. On the tenth pace, the contestants turn and fire. If a musket (or pistol if a functional one can be devised) misfires, it may be reloaded. If no one is hit on the opening volley, the contestants reload and fire again. This repeats until one contestant is the victor.