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Fixing a Loose Ruger® MK IV™ Main Spring Tube

Before We Begin


  • Always make sure the firearm is unloaded before performing any work it!
  • Remove all ammunition from the work area before working on any firearms.
  • Always wear safety glasses when performing any work on a firearm.

Video Instructions

If a customer is experiencing a gritty feel, grinding sounds and/or light strikes with their Ruger® MK IV™ - the mainspring tube is the first thing to check. Tools needed include a rubber mallet, needle-nose pliers, 3/32" punch, 5/32" Allen wrench, 3/32" Allen wrench, 1/16" Allen wrench, keeper pin, and red Loctite®.

Tools Needed

  • Rubber mallet
  • 3/32" pin punch
  • 1/16" Allen wrench
  • 3/32" Allen wrench
  • 5/32" Allen wrench
  • Needle nose pliers
  • Red threadlocker
  • Tape (optional)


Step 1

Separate the pistol upper and frame.

Remove 4 grip screws using the 3/32 Allen wrench and then remove the grips from the pistol's frame.

Remove the bolt release from the frame.

Optionally, place tape over both ends of the sear pin to keep it from falling out of the frame.

Step 2

Move the safety lever to the fire position.

Use the thumb of your non-shooting hand to put pressure on the hammer. Then, pull the trigger to release the hammer.

Step 3

Remove the screw holding the safety lever from the right side of the frame.

Remove the Right Safety Lever.

Using the 3/32" punch, push the Safety Lever out of the frame. Hold onto the Hammer while removing the pin as it is under spring tension.

Remove the Hammer and Safety from the frame. Pivot the Disconnector forward and then remove the trigger spring and trigger spring plunger.

Step 4

Use the 3/32" punch to push the Bolt Stop Cross Pin out of the frame. Hold onto the Bolt Stop Pin while removing the punch to retain the parts.

Pull up on the Latch Button and Main Spring Housing to separate the main spring assembly from the frame.

Step 5

Pull the factory Bolt Stop Pin up to separate it from the main spring assembly.

Slide the Latch Button to the rear to separate it from the Main Spring Housing.

Be sure not to lose the two Latch Springs that were captured between the Latch Button and Main Spring Housing.

Step 6

Use the 5/32" Allen wrench to unscrew the tube from the rear of the Main Spring Housing. This tube is under spring pressure, so be careful to retain it the tube, body, and spring.

Clean the inside of the tube as well as the mating threads. A cotton swab can be used to clean these areas.

Apply a generous amount of red threadlocker to the outside threads of the tube.

Insert the spring back into the tube and screw it back into the Main Spring housing. Use the 5/32" Allen wrench to make it snug, but not excessively tight.

Step 7

Make sure the two Latch Springs are inserted into the corresponding recesses on the Latch Button.

Slide the Latch Button back into the Main Spring Housing, taking care to make sure that the ends of the springs sit over the raised bumps on the Main Spring Housing.

Use your thumb and index finger to squeeze the Main Spring Housing and Latch Button together, then insert the Volquartsen Bolt Stop Pin into the main spring assembly. The flat face of the Bolt Stop Pin should face toward the long leg of the Main Spring Housing.

Insert the Keeper Pin through the hole in the Main Spring Housing and Bolt Stop Pin. It should be centered in the assembly.

Step 8

Make sure that the sear is pivoted up and forward before proceeding to reassemble the frame.

Make sure that the V-Lock Retainer Spring is pivoted back to touch the Keeper Pin and then slide the Main Spring Assembly back into the frame.

Line up the holes in the frame with the Keeper Pin and then reinstall the Bolt Stop Cross Pin into the frame with the mallet. This will drive the Keeper Pin out of the frame.

The legs of the V-Lock Retainer should click into the grooves on the Bolt Stop Cross Pin. You will need to use the pin punch to drive the Bolt Stop Cross Pin far enough into the frame, as it sits slightly recessed in the frame. When inserted correctly, it should be recessed the same amount from both sides of the frame.

Step 9

Hook the safety over the sear on the left side of the frame. Then pull the safety forward until the Safety Lever can be inserted partway through the frame. Only insert the Safety Lever far enough to catch the safety, we'll push it the rest of the way through later.

Insert the Trigger Spring into the trigger and insert the Trigger Spring plunger into the Trigger Spring.

Take the Hammer in one hand and prepare to install it. Make sure the Hammer Strut is facing down and to the rear, so that it will engage the Main Spring when installed.

Pivot the Disconnector back, and align the Disconnector, hammer, and frame so that you can push the Safety Lever through the frame.

Screw the Right Safety Lever back onto the Safety Lever.

Perform a function check of the Safety, Trigger, and Hammer to ensure proper operation of the frame.

Step 10

Slide the Bolt Release back onto the frame.

Reinstall the grips and screw them back to the frame.

Reinstall the upper onto the frame.

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