Installing a Timney Trigger on the Ruger Model 77 Mark II Rifle

The Ruger Model 77 MKII trigger assembly is a basic three-piece design including the sear, trigger, and spring. The factory-installed trigger on the Mark II has no provision for adjustment, except for what can be accomplished with spring replacement. For the best accuracy and ease of use, this rifle fairly begs for a highquality aftermarket trigger assembly. My personal choice for this rifle is appearance to the original factory parts.

Both the trigger and sear offered for this model are cast of 440C stainless steel hardened to 58-60 RC and surface ground to exact geometric tolerance. Timney provides comprehensive instructions for installation of the Ruger M77 MKII trigger and sear. Removal of the old parts from the receiver is simple. Each is held in place by a free-floating pivot pin. First, the trigger-retaining pin is pushed out, and then the trigger falls free of the hanger along with the spring.

The Right and far The sear-adjusting set screw on the Timney is not clearly seen in this profile view. sear is then removed by pushing the pivot pin outward and lifting the sear upward from its milled slot in the receiver. Installation of the new sear, spring, and trigger are performed in the reverse order. With the Timney trigger, there’s a spring included that provides an adjustment between 1-1/2 and 2 pounds.

For a heavier pull, the original Ruger trigger spring can be used, although to a degree, at least, this defeats the purpose of installing a custom trigger. The trigger spring is adjustable from below with a screw on the lower side of the trigger. An Allen wrench is provided for this purpose. The rifle can now be cocked and fired, but the safety will not work at this point. The next step is to double-check the sear-trigger engagement. Timney has a unique method of adjusting this.

A small set screw protrudes diagonally through the front portion of the sear enabling it to push on the trigger. The set screw is readily accessible through the firing-pin slot in the bolt channel. Through trial and error, the sear can be precisely adjusted with a small Allen wrench. However, the sear engagement has been factory set, so unless you are knowledgeable in this area, leave things alone. Any final adjustment and fitting of the safety must be performed after the sear is adjusted.

Both the sear and trigger are highly polished on the working surfaces for a smooth, crisp release.

The two floating pins at the side of the action are pushed out to remove the trigger and sear. The rotary trigger-locking mechanism engages the tab on the trigger, preventing the rifle from firing. The Timney’s safety function works on the same principle. The set screw and nut on the trigger tab are used to adjust over-travel. With the trigger and sear in position and adjusted, it’s time to fit the safety and trigger assembly. While this is not especially difficult, it does require extreme care.

First, the bolt is installed with the trigger and sear cocked. You’ll note that the safety cannot be engaged at this point. Metal must be removed from the safety tab of the trigger where the rotary safety selector makes contact. In the instructions that come with the trigger, mention is made of using a file here. On the trigger I installed, 0.035 inch of metal had to be removed from the safety tab before the safety selector could be turned into position.

In my experience, 0.035 inch is a lot of filing to do while still keeping the surface on the safety tab square. Instead, I used an end mill with the trigger held perfectly square in a mill vise. Re- The Timney sear shows the rounded set screw protruding through, which is used to precisely adjust sear/trigger engagement. I moving too much from the safety tab" even as little as 0.005 inch too much" can render the safety ineffective, so proceed with caution.

With the safety tab properly fitted, try the action and trigger several times. Use the slam-fire maneuver as the bolt is opened and closed rapidly. The rifle must not discharge. Also, place the safety in the "on" position and pull the trigger. Then release the safety to see if this would cause the gun to fire. It should not, of course. Try all these things several times to be certain the gun is safe. Further adjustments can be made after the safety is properly fitted but before the action is replaced in the stock.

These would include the adjustment of trigger overtravel and the trigger spring. It may be necessary to inlet the stock below where the overtravel adjustment lug enters the stock before the action is placed in the stock. A small, sharp chisel is probably all you would need for this. The over-travel adjustment consists of a lock nut and set screw located at the left side of the trigger that come in contact with the action. This setting is made by trying the screw contact as the rifle is cocked and fired.

Lock the nut after the desired trigger travel is attained. The action can then be placed in the stock, ready for use. Conclusion Converting an essentially non-adjustable, 5-pound factory trigger to a safe and crisp pull weight of 1-1/2 pounds is sure to make your customer happy, and it’s relatively simple to do with this innovative design by Timney. Just for your information, Timney will install the trigger for $30 plus $8 to cover the return shipping.

Since it would cost at least an additional $8 to ship the rifle to Timney, with no guarantee of how long it will be before the rifle is returned, my feeling is that you should be able to charge $50 or more for the installation. And that’s not too bad for what should be less than a hour’s work.