Servicing The Timney M510 Trigger

Here I will discuss the Model 510 Timney trigger as installed on a short action Model 700 Remington rifle chambered in .22-250 Remington. The rifle was equipped with a 1:10 twist Douglas premium barrel and used for both targets and varmints where accuracy is essential. As received, the Timney M510 trigger was set at 1.6 pounds. The trigger was very dirty and the firing pin would sometimes fall on bolt closure, particularly if a slam-fire maneuver was used.

I began by thoroughly cleaning the trigger using lacquer thinner, a brush, and 80 pounds of compressed air. I then gave the trigger a thorough inspection. I couldn’t recreate the slam fire or failure to cock on bolt lift. Sometimes cocking a rifle and pulling the trigger with the safety on, followed by releasing the safety, will cause a lightly set trigger to fire the rifle, but this rifle passed that test.

In any case, I felt this trigger should be adjusted to just over two pounds which was accomplished by both increasing trigger spring pressure and sear/trigger engagement. At top center the sear/trigger inspection port is shown with rifle cocked. Adjustment of the M510 trigger requires use of all these tools. The Model 510 Timney trigger is equipped with socket head lock nut screws in 1/16" and 1/8". The larger 1/8" is for overtravel and the smaller two control sear/trigger engagement and trigger spring pressure.

Turning the sear engagement screw inward will cause a cocked rifle to fire. Turning the trigger spring inward will increase spring pressure and trigger pull. Of course, before beginning any disassembly, maintenance, or adjustment unload and clear the firearm. To begin the adjustments, I back off the sear/trigger adjusting screw a full turn, cock the rifle, and then view the sear trigger engagement

Left, clockwise: These three sequential pictures show the position of the sear and trigger from pre-cocking through trigger/sear release. On left, as the rifle is cocked the sear moves forward over the top of the trigger. Center, the sear at this point overrides the trigger, then cocking the rifle. The degree of override has an effect on trigger pull force. Right, the rifle is fired here.

Note the released sear falls below the top plane of the trigger, enabling the firing pin to thrust forward. through the small hole located at the top of the trigger housing. At this stage you will note the upper rearward part (the sear) at the top of the trigger well engaged. Now turn the sear screw very slowly inward until the rifle fires. You can then attain the desired sear/trigger engagement you want by backing off this screw about a full turn and rechecking things through the viewing aperture.

At this stage, take a trigger pull force reading as sear/trigger engagement alone has a bearing on pull weight. If it is not quite where you want it, adjust the trigger spring by 2.2 oz. loosening or tightening it. Adjust this spring accordingly to the desired pull weight you want. As the rifle fires, you will note the sear positioned downward and rearward of the trigger as you view through the aperture. Experimenting with the spring tension and sear/trigger engagement will give you the pull weight you want.

Just be sure you are working with a clean trigger. With most triggers you will not be able to visually observe the working of the sear and trigger but this is what takes place during adjustment. Trigger Lubrication There are a few special trigger lubricants on the market. Differing schools of thought surround the use of trigger lubricants. Some feel that any and all lubricants will eventually congeal and gum up.

Temperature changes will affect most forms of lubrication applied to the trigger as well, which must be considered as conditions change. Almost all forms of lubrication will change over time. Over more than 50 years of working with a variety of hunting and target triggers and shooting under temperature extremes, here is my thinking on trigger lubrication: A totally clean trigger with a thin synthetic lubrication will function for at least a year with no problems. One caveat must be observed here.

Avoid all bore cleaning materials from entering the trigger. As a bore cleaning brush soaked with liquids is passed over the exposed trigger and sear, there will invariably be spillage into the working parts of a trigger. This attracts foreign materials and trouble is sure to follow. Always use a bore guide where you can as a preventative measure. Conclusion There are no real mysteries involved with proper care, cleaning, and adjustment of most triggers.

Triggers will vary widely and require a careful study of each their function. I have had good success cleaning triggers with lacquer thinner and compressed air, followed by a drop or two of lubricant forced into the trigger with compressed air. If you lack experience adjusting triggers, don’t take chances as problems can arise. Talk things over with a qualified gunsmith if in doubt or have one do the job. AG