September 23, 2013

Servicing The Ruger Mini-14

Due to the factory’s penchant for in-house repairs, there are limits to what you can do with the Mini-14.

Ever been asked why the Mini-14 isn’t called the Mini-.223 or Mini-anything else? Take a look at one next to an M14. In general appearance, the Mini is a smaller, lighter ringer for the rifle the U.S. Military rediscovered during Desert Storm. It even functions much the same.

To wit, when a cartridge is fired, propellant gas is bled off through a hole in the barrel. The gases pass through the gas-block assembly to push the gas piston rearward. This drives the slide assembly back about 5/8-inch to cam the right-hand lug of the bolt. The bolt then begins to rotate counterclockwise, unlocking it from the rifle’s breech and extracting the fired case. At the same time, the ejector plunger and plunger spring press forward against the base of the cartridge to throw it clear of the rifle.

The rearward travel of the bolt also compresses the recoil spring and pivots the hammer into engagement with the secondary sear, which holds the hammer to the rear. When the compressed recoil spring starts moving the bolt forward, the bolt strips a fresh round from the magazine, feeds it into the chamber, and rotates clockwise to lock up. During lock up, the ejector spring is compressed, allowing the cartridge to be seated against the bolt’s face as the extractor captures the cartridge rim. The trigger, having been let go to its forward position by the shooter, enables the primary sear to engage the hammer’s lower hook in the ready-to-fire position.

Courtesy, American Gunsmith Book of the Rifle

Courtesy, American Gunsmith Book of the Rifle

The Ruger Mini-14 is a basic, easy-to-work-on firearm.

The double function of the safety in the Mini-14 is to slightly retract the hammer and lock it to the rear while a secondary surface on it blocks the trigger.

Total Take-Down, Limited Service

Due to Ruger’s intense preference for factory-only repairs, what you can accomplish with a Mini-14 is limited. Beyond removal of dirt and burrs, you’re pretty much restricted to replacing parts—if the parts aren’t restricted. And unless you understand how to detail strip the rifle and put all its parts back together again, you can’t even do that. Much of what you need to know can be found in books dedicated to firearm disassembly, but in the case of the Mini-14, you need to know more than they’ll tell you. So let’s go through the disassembly and reassembly one group at a time:

The Stock Group. Remove the two reinforcement screws and lock washers. Compress the ears of the stock reinforcement and remove it. Reach in from the magazine well, press the forearm liner’s locking tab upward, and move the liner forward for removal.

In reassembly, tap the cap of the liner to seat it firmly into the tip of the forearm. The stock reinforcement must fit flush inside the stock. If it doesn’t, interfering wood should be removed—carefully—to achieve the prescribed fit.

The Bolt Lock. The stock, stock recoil spring, slide, and bolt should be removed from the action first. Use a 1/8-inch punch to tap the lip of the lock cover plate downward, and remove the plate from the receiver. Hold the bolt-lock plunger down while removing the assembly from the receiver, then take out the plunger and its spring.

When reassembling, make sure to start the narrow end of the spring on the plunger shaft, and position the notch in the plunger to point rearward toward the receiver’s bolt-lock recess. Holding the plunger down, install the bolt-lock assembly so the plunger tab in the lock engages the notch.

Trigger Group. Cock the hammer, swing the trigger guard down, and place the safety in the off position. Insert a 1/16-inch punch or pin into the hole under the hammer spring and pull the trigger. The hammer will fall. Now remove the hammer strut/spring assembly. Drift out the hammer-pivot pin to remove the trigger guard and hammer from the housing. Ease the trigger spring tension by pressing down on the trigger, then drift out the trigger-pivot pin. After removing the punch, lift out the trigger and secondary sear subassembly.

Further take-down of the sear, trigger and trigger bushing isn’t absolutely forbidden. It’s just not recommended. Neither is removal of the magazine latch. But if one of the latter’s parts is broken or damaged, use a punch to drive the latch’s pivot pin out right to left. Hold the latch in position, then remove the punch, latch, and latch spring in that order. A punch is also employed to remove the safety-spring retaining pin and safety-detent spring, after which you can take out the safety.

On reassembly, a 0.125- by 0.310-inch slave pin is used to preassemble the magazine-latch spring to the magazine latch. After installation, the slave pin is driven left to right with the magazine-latch pin. The safety should be forward before the hammer is inserted back into the housing. After the hammer pin is reinstalled, rotate the hammer forward to allow insertion of the upper portion of the hammer strut into its recess in the hammer. The hammer is then full cocked so its hook engages and is captured by the secondary sear.

Bolt Group. Push down the extractor plunger and use the blade of a screwdriver to rotate the plunger until its lip rests on the extractor. With the same screwdriver, lift the extractor out of the bolt. Remove the extractor plunger and spring, the firing pin, and the ejector plunger and spring from the bolt body.

If, due to damage, the extractor must be replaced, dress down the sharp edge of the new part a tad during reassembly.

Gas Block Group. There are four screws to deal with initially. You gradually loosen them, moving from one to another in an “X” pattern with a 9/64-inch Allen wrench. Once the screws are out, the gas-block cap and lower gas-block subassembly can be removed. Be careful you don’t lose the gas-port bushing.

During reassembly, it’s critical to maintain alignment between the gas-port bushing holes in the lower gas block and the gas piston. Also, the lower assembly must seat flush with the barrel. This can only happen if the protruding portion of the gas-port bushing is seated into the barrel’s gas-bushing hole. Failure to properly seat the gas-port bushing can result in damage to the barrel. When reinstalling the four set screws, use the same, gradual “X” pattern to achieve a uniform gap between the gas-block cap and the lower block. It wouldn’t hurt to stake those screws in the gun to prevent them from loosening, either.

Inspection of Components

Look over the bolt for cracks or battering, then check the rear of the bolt near the firing pin for signs of peening. Minor peening can be dressed down with a file and stone to blend in. Also remove any burrs that might interfere with the firing pin’s movement. Before removing the extractor from the bolt, it’s a good idea to look for signs of weak extractor spring tension. The tip-off is limited motion of the extractor. If that’s the case, replacement of the spring and its plunger is required.

The slide assembly should be checked for signs of excessive wear in the area of the cam pocket. Slides so damaged should be replaced. And if there is damage to the muzzle beyond your recrowning capabilities, the entire rifle should be sent to the factory for service.

Next is the gas-block assembly. Any cracks or damage? Replace it. How about the rear sight? Windage and elevation adjustment screws should have full movement. Rear sight housings should fit tight in the receiver. If they are loose, the housing’s front locking tab is probably worn and the housing should be replaced.

Gauges and Gauging

Ah, here’s the rub. A complete set of Ruger factory gauges costs almost 500 bucks, and they’re only sold to police armorers. All is not lost, however. Headspace gauges for .223 caliber are available from Brownells. They also offer a firing-pin protrusion gauge. It’s much simplified compared to the factory’s, but is much better than nothing at all. If you can’t make the bore gauges mentioned here, maybe you can have them made or borrow them from a Mini-equipped law-enforcement agency.

Headspace is measured with a 1.4636 Go gauge, a 1.4694 No-Go gauge, and a clean, empty chamber. If the bolt closes completely on the Go gauge with no resistance whatsoever, no problem. If it closes on the No-Go, or if the bolt roller travels past the corner of the locking cam on the slide-cam pocket, it’s a major problem that requires factory resolution.

Bore straightness is measured with a drop pin 4 inches long by 0.2170 inch in diameter. The bore must be clean and dry. The pin is inserted at the muzzle end. Failure of the pin to pass freely through the length of the barrel leaves you with two choices: Either send the rifle to Ruger for a barrel straightening job, or send the rifle to Ruger for a new barrel.

A breech-erosion gauge is 51/2 inches long by 0.220 inch in diameter. A line is scribed fully around it, 2.180 inches from one end. This is the “reject” line. The gauge is inserted into the clean bore of the rifle from the breech end until slight resistance is felt. No force is required or used. The measurement determining the degree of gauge entry is made against the rear surface line of the forward receiver and the reject line. If that measurement shows the gauge has entered to the reject line, it indicates a need for rebarreling.

To check firing-pin protrusion, remove the bolt from the rifle, place Brownells gauge into contact with the recessed bolt face, and hold it there. Use a suitably sized punch to press the firing pin forward until it is flush with the rear of the bolt. Remove the gauge and measure how far its button has moved forward to determine the amount of driven firing-pin protrusion. It should be 0.029 inch minimum, 0.033 maximum. Reset the gauge and press hard on the rear of the firing pin, forcing it to its extreme forward position. Measure protrusion against the 0.032-inch minimum and 0.042-inch maximum factors. Firing pins failing to fall within the above parameters should be replaced and refitted. In refitting, assure that a 0.020-inch minimum gap exists between the rear of the firing pin and the face of the hammer.

Unlike the Ruger 10/22, there are few, if any, aftermarket components available to improve this rifle’s performance—other than alternate sights and cosmetic add-ons. That day may be coming to an end, however, for I have heard some rumors to the effect that the Mini-14 will soon be available with a heavy barrel. That alone could serve to greatly enhance its accuracy, and thus its popularity.