The M5 Stuart Project - Installing the Paintball Marker


WARNING: To ensure everyone understands, this stuff worked for me, but I can't guarantee it'll work for you. If you decide to start hacking your tank and your paintball marker, be aware that you can really screw them both up if you're not careful or if you don't understand what you're doing! I can't (and won't) be held responsible for your actions! Needless to say, taking the tank or the paintball marker apart voids the manufacturer's warranty...


As recommended by Joe Sommer, the Splatmatic XJ40 40 caliber paintball marker was chosen for the project due to it's size and relatively low cost ~$40. Check ActionVillage or Cabelas as a source. The gun will be heavily modified so there's no going back once you start this! The gun is mounted on it's left side in the turret to allow room for elevation.

The first step in the conversion will be to move the cocking know from the left to the right hand side of the gun. The gun is mounted in the turret on it's side to allow room to elevate the barrel in the turret. You need to be able to cock the gun when mounted in the turret.

Here's the gun field stripped. Pretty simple design. Keep the parts clean. Look closely at the pic and you'll see the slot in the receiver where the cocking knob rides.


That slot needs to be moved to the other side of the gun so it's on top once it's mounted. The gun has to be mounted on it's left side since the paintball feed port is on the right. Choose a drill bit about the same size as the slot, align with the ends of the existing slot, and drill through the other side of the receiver.

Use a fiber cutoff wheel in the Dremel tool to cut out the material in between the holes. A little black laquer will fix up scratches! Use a small flat file to smooth out the cutout.

Next step is to move the cocking knob from the left to the right side of the bolt. It's 10-32 so just carefully drill straight through the existing hole to the other side and tap the hole. After the drilling and tapping, make sure you clean the parts really good. Metal chips in a paintball gun won't go over well.

Next step is to trim down the trigger housing. You don't need the grip frame in the tank! Use the Dremel tool and some sandpaper to finish up.

A servo has to be mounted to pull the trigger. I used a piece of flat aluminum to mount the servo and socket head screws through the trigger housing. Just watch out and don't drill into the trigger or sear! I removed the safety and spring as it's not needed. Note the servo arm is rounded like a cam.

Here's the back side of the trigger servo. Pretty straight-forward mounting.

The gun needs to pivot in order to allow elevation and depression. I made a couple of pivots out of 1-1/2" aluminum angle. The gun balances near the top forward feed port retaining screw and across to the bottom of the trigger housing. I just drilled into the bottom of the housing and tapped it to accept a 10-32 socket screw.

This pic shows the left side pivot. I simply drilled out the existing screw hole and tapped to 10-32 for the pivot point. In this view, you can see the elevation/depression servo.

View from the front. Here you can see the two pivots and both servos. The turret allows the gun about 9 deg of elevation and 6 deg of depression. The gun is suspended at the pivot points about 1-3/16" above the base of the turret.

Here's a detail shot of the elevation servo. It's directly connected to the marker through a 2-56 machine screw. The servo has a 1" travel at the end of the control arm. I selected the point on the marker to install the screw that corresponds to 1" of travel. A slot was cut in the end of the control arm to allow the screw to slide back and forth as it moves up and down.

Now the top of the turret needs to be gutted. First remove the stock electronic trigger, mantle, and gun barrel. The web that runs across the turret needs to be removed as well as most of the plastic up in the front where the stock trigger mounts.


Here's what you end up with. You're basically opening up the shell. Don't worry about the stock mounting bosses. The top of the shell must be removed to install a new CO2 cartrige anyway. I plan to use small aluminum angles mounted to the turret base to allow me to put screws in the side of the turret shell to hold it on but allow it to be removed easily.

The stock Stuart turret has the hatches in the top which make it easy to get to the gun to cock it as well as to load it. Next step is to build a magazine.

The business end. Note the plastic that has been removed to clear the gun. I ended up rotating the C02 clasp (see next pic) to provide clearance at the side. On the original marker, it would be on the side instead of the bottom.

Next step is the barrel. I have a lathe so I made a simple adapter to allow use of a piece of 1/2" x .035 aluminum tube for the barrel. The paintballs are 0.4" nominally so there's 0.030" clearance through the tube.

Here's the barrel installed. Press fits into the adapter. The adapter is attached to the muzzle of the paintball marker with a couple of 4-40 socket head machine screws. I turned a small alignment shaft out of aluminum to keep the adapter aligned with the bore while drilling and tapping the adapter to the marker.

Krylon OD camo paint matches the Stuart nicely.

Now to cover up the unsightly hole in face of the turret with a revised mantlet. To start, I cut the back end off the stock Stuart barrel and bored it out to 1/2" with a drill and dremel tool so it slips over the 1/2" aluminum tube barrel.

Next, I hacked up the stock Stuart mantlet so it would fit over the new barrel and move freely in front of the turret. I epoxied the cut portion of the barrel to the mantlet. A lot of trial and error fitting occurred here...

Even with the revised mantlet, there was a pretty good gap left at the front of the turret so I made a simple wood mold and vacuum formed a piece of ABS plastic to make a rounded hood for the front of the turret.

This is how the turret looks with the added hood epoxied in place. .

Slip the revised mantlet over the barrel and there you have it...

Another view of the mantlet and hood. Not exactly scale but then Stuart's didn't have paintball markers in the turrets...




OK, now with the cosmetic stuff out of the way, I needed a magazine for the paintballs. This is what I came up with and it's made of thin (0.016) 2024 aluminum.

It's a single layer and holds around 50 paintballs max. It pivots at the front to stay with the marker as it moves up and down. The back end is elevated to ensure feed at all angles. A slip on cover keeps the paintballs inside.

The magazine can be loaded (and the marker cocked) without removing the turret top by reaching in through the existing hatches. I used a piece of 1/2" tube to make a quick loader that holds exactly 40 paintballs.

Here's a view with the cover off the magazine.

In this view, just in front of the magazine, you can see a vertical piece of aluminum bar that I used to secure the top of the turret to the turret base. A single 10-24 socket head machine screw holds the top of the turret on making it easy to remove.

The assembled turret looks very close to the original and it functions quite nicely!

  More to come as I complete the radio installation in the turret.