In part 2 we looked at the adjustable disconnector, which is an easy feature to spot. The next thing we will look at is Grit. Grit is more of a feel than something you can point to, unless the machining is really poor.
When you pull a trigger, you have the hammer and the trigger hooks being pressed together by the force of hammer spring. The hammer spring is not a weak spring. Add in a little pressure from the trigger spring. The result is a lot of pressure on the hooks, at the same time the trigger is turning on the trigger pin. This happening in the first stage of a 2 stage trigger. On a single stage trigger it’s happening all the way up to the time the hammer is released.
There is a lot going on inside your receiver. When all the parts are accurately machined, the pull of the trigger will feel smooth and it will move with no jerking or skipping felt by your trigger finger. When the parts are not well machined your trigger finger will feel a jerking and skipping. It can also give you a feeling of grinding. This is what we mean when talking about Grit.
With that long definition of grit, let’s look at how you can stop it and how to avoid it in the first place.
When you install a new trigger in your rifle, you may think you have some grit. After a few rounds it goes away. That is not grit, That is the break in period. What you’re doing is wearing off the finish on the hooks and pins, with the hardened hooks polishing and mating themselves to each other. This is a lot like installing a new cam and lifters in a race engine. Please don’t confuse this with the grit from poor machining.
If after the break in you still don’t have a smooth feel you may have a problem.
Here are some of the places to check, with possible solutions.
1. Check the hooks. If you can see machining lines you can try to polish the hooks to get a better finish. If you do this be careful not to take off too much material or create a slanted surface.
2. Check the trigger pin. When installing the trigger, you may have scraped off a small amount of the anodizing from the receiver. An easy way to check is to pull the hammer out and see if you still feel the grit. With the hammer out, you will have no hook to hook contact. Any grit you feel will be in the trigger pin area. Check that the pin is not damaged. If it’s not damaged, clean the pin and the trunnion and reinstall the trigger. If you have a damaged pin, replace it before reinstalling the trigger.
3. If you have completed step 2 and cleaned and reinstalled the trigger but you still have some grit, check the tail of the trigger. Not all AR-15 lower receivers are machined the same. One of the spots the manufactures may miss is the radius to the rear of the safety selector. This usually is not a critical dimension, but with some 2 stage triggers the tail is a bit thicker. If the rear radius is not properly cut, the trigger tail may be touching the receiver.
4. This probably should be number 1. Give the whole lower receiver a good cleaning after the break in. You may have some of the finish or even some of the anodizing from the receiver stuck in the trigger.
What do we do at The Wisconsin Trigger Company to avoid grit? Starting with the hooks, all M-K hooks are machined as precisely as possible. We do not EDM our triggers. We cut and grind them as needed, the old fashioned way. Some companies manufacture EDM the whole trigger, then increase the cutting speed to get the production time lower. This will give you an adequate finish but this is not up to our standards.
One of the other places we give attention to is the trunnion and the pins. Our pins are manufactured on the latest Swiss style machines. This assures we are getting round, straight and accurately dimensioned pins. A well machined pin will do you no good if you put it in an incorrectly shaped, poorly finished trunnion hole. Some manufactures fall back to the EDM to cut the hole. Once again, we do not. The trunnion holes on all M-K triggers are drilled and reamed. Then they are honed to size with a diamond hone. This gives us a straight, round, correctly sized hole, with a finish as smoother then you get with an EDM.
The tail on all the M-K triggers are cut down slightly on the right side. You may still find a receiver that they will rub on. There is not much we can do about that. If you do have this problem it is perfectly acceptable to remove some of the material from the side of any model M-K trigger. Take off just enough to gain the clearance needed. I do not know if any other triggers out there can be fit to a out of spec receiver this way. If you are not fortunate enough to have an M-K trigger please contact the manufacturer of your trigger to see if this is possible.
Some of the M-K triggers can be equipped with an option called “The Bronze Advantage”. We enlarge the trunnion hole and press in bronze bearing material, then machine the pin hole the same as a standard trunnion. The advantage to the bronze advantage is even less friction on the pin. The bronze will also hold much more lubricant than steel will hold.
If there is a good clean installation of a quality built trigger, you should have no issues with grit.
One of the less considered aspect of a trigger is Overtravel. Overtravel is the distance that the trigger will continue to travel after the hammer has been released. Overtravel is set by the height of the tail. This is on most 2 stage and most single stage triggers. Some triggers such as the M-K IIA3 and the
M-K X triggers have adjustable overtravel. There is no right or wrong. There is only what you like and what feels good to you. Most shooters don’t even think about it. They just shoot whatever they get. The average Target and Speed competitors don’t think about it either. Most of the top competitors do think about it and what I have been told by them is what I cover in the next chapter.