Tippmann 98 Custom Platinum Series ACT Paintball Gun

Inside the gun

How the Tippmann 98 Custom Works

The Tippmann 98 Custom is a mechanical, open-bolt blowback gun. When you pull the trigger, a spring throws the rear bolt forward into the valve. The valve lets out a burst of air that fires the paintball, and part of that same burst pushes the rear bolt back until the sear catches it, which cocks the gun for the next shot. There is no battery and no circuit board in a standard 98. Every shot powers the one after it.

The firing cycle, step by step

1. Ready 0:00

   The gun is cocked. The drive spring behind the rear bolt is squeezed tight, and the sear is holding the rear bolt back. The linkage arm ties the front bolt to the rear bolt, so the front bolt is back too. That leaves the breech open, and a paintball drops in from the feed elbow. This is what open bolt means: between shots, the bolt waits in the open position.

2. Release 0:02

   Pulling the trigger moves the sear off the rear bolt. Nothing is holding the bolt back anymore, so the drive spring shoves it forward.

3. Chamber 0:03

   As the rear bolt moves forward, the linkage arm pulls the front bolt along with it. The front bolt slides forward over the power tube, pushes the paintball out of the breech into the back of the barrel, and closes off the feed elbow so the next ball has to wait its turn.

4. Gas pulse 0:05

   At the end of its travel, the rear bolt slams into the back of the valve and knocks it open for a split second. Air from your tank has been sitting in the valve, fed up through the braided gas line from the grip. It rushes forward through the power tube, out the front bolt, and pushes the paintball down the barrel.

5. Blowback 0:06

   The valve does not only send air forward. The same burst pushes back on the rear bolt and drives it rearward, squeezing the drive spring again. That is the blowback in a blowback gun: the shot itself recocks the gun, so you never have to pull the bolt handle between shots.

6. Reset 0:08

   The sear catches the rear bolt and holds it. The linkage arm drags the front bolt back and opens the breech, and the valve spring snaps the valve shut. The next paintball drops in. When you let go of the trigger, the trigger spring pushes it forward again, and the gun is back where it started.

The parts that make it work

Part names follow Tippmann's own 98 Custom Platinum Series owner's manual, so they match what you will see on a parts list.

Rear bolt

The heavy piece the drive spring throws forward. It acts as the hammer that opens the valve, and it is the part the sear catches to hold the gun cocked.

Drive spring and guide pin

They sit behind the rear bolt, held in by the end cap. The spring stores the energy that snaps the rear bolt forward on every shot.

Sear and trigger

The sear is the small catch under the rear bolt. The trigger moves it out of the way, and the sear spring and trigger spring push both back into position for the next shot.

Linkage arm

A thin arm running along the top of the internals. It connects the front and rear bolts so they move as a pair.

Front bolt

Slides back and forth over the power tube. It loads the paintball into the barrel, seals off the feed elbow while the gun fires, and carries the air to the back of the ball.

Power tube

The tube the front bolt rides on. The valve sits inside the back end of it, and it carries air from the valve up to the front bolt.

Valve

Holds tank air until the rear bolt knocks it open. Inside are a plunger, a spring and seals that close it again after each shot. Tippmann does not recommend taking the valve apart.

Gas line

The braided hose that carries air from the tank adapter in the grip up to the valve.

Velocity screw

On the left side of the receiver. Turn it in (clockwise) to lower velocity and out (counterclockwise) to raise it, using the 5/32 inch Allen wrench that comes with the gun. Tippmann says never to remove the screw, and never to shoot faster than 300 feet per second.

Bolt handle

Pull it all the way back to cock the gun before your first shot. After that, blowback does the cocking for you.

What ACT changes

ACT stands for Anti-Chop Technology, and it is the main difference between the ACT and non-ACT versions of the 98 Custom. On a standard 98, the linkage arm locks the front and rear bolts together. If a paintball is only partway into the breech when you pull the trigger, the front bolt closes on it and breaks it. That is a chop, and it means paint in your barrel and shots flying off target until you clean it.

On an ACT gun, the linkage arm rides in a groove in the rear bolt and is held there by a spring instead of being locked in place. If the front bolt runs into a ball that has not fully dropped, it stops against the ball with only light spring pressure while the rear bolt keeps going on its own. The rear bolt still opens the valve and still blows back, picks the linkage arm back up, and pulls the front bolt open so the ball can settle into the breech. You lose that one shot, but you keep the ball in one piece, and Tippmann notes that you do not have to recock the gun after the ACT steps in.

What the firing cycle tells you when something goes wrong

It fires on its own or will not stay cocked

The rear bolt is slipping past the sear instead of being caught at the reset step. A worn sear or a worn rear bolt is the usual cause, and both are inexpensive parts to replace.

Velocity is low or jumps around

Check the velocity screw first, then your air. CO2 loses pressure as it gets cold, so velocity tends to drop during fast strings of shots and on cold days. Chronograph the gun before you play either way.

It leaks or does not cycle right after you had it apart

Look at the external valve O-ring and the gas line where it screws into the valve. Tippmann's manual warns that a damaged valve O-ring will keep the gun from working correctly.

Keeping the cycle smooth

A few drops of paintball gun oil on the front bolt O-ring and the rear bolt O-ring keep both bolts sliding freely. Tippmann also recommends storing the gun uncocked with the bolt forward, which keeps the drive spring from sitting compressed between games.

Sources

• Tippmann 98 Custom Platinum Series owner's manual (operation, parts list, velocity adjustment, maintenance)