I got a new CZ Scorpion EVO carbine for Christmas. The trigger was heavy and gritty as expected, but I was also picking up some unwanted "trigger sting" as well. Something in the action was communicating quite a bit of "impulse energy" to my trigger finger when I fired a round. Given that I was expecting a 9mm cartage in a heavy rifle to feel a bit like shooting a BB gun, I was a bit aggravated. My SKS, AK47, and AR15s triggers never had "trigger sting". I have not seen anyone discuss this particular aspect of trigger performance. Fortunately this seemed to disappear with the modifications that I did. I don't know which mod did that.
I first smoothed the trigger surfaces as per the youtube video (I used 2000 grit sandpaper to polish, not remove metal). I also replaced the stock 10 lb. trigger spring with a commercially available 5 lb. version and that got rid of the heavy, gritty trigger pull. The trigger was now much better.
However, the trigger pull was *very* long. I found myself pulling halfway, then finishing off the trigger pull as I got a good target sighting. Likewise, the trigger reset was also very long, reseting only after about a 2/3rds trigger release.
Here is a quick write up on what I did to help this.
I removed
~41% of the trigger pull length by placing a 1/8" x 3/4" x 0.016" brass shim under the trigger feet at the rear of the trigger. I experimentally found that raising the two rear trigger feet by ~ 0.039" released the hammer, so 0.016" gets me close to removing half the trigger pull. I cannot go higher than this and have the safety lever still work as the safety needs to clear the top of the right rear trigger foot near the disconnector spring. 0.016" brass is pretty workable, so I was able to cut it out with scissors. Since it was then all warped and curled, I flattened it by rubbing it flat against a hard surface using the butt of a large drill bit. It is important that it is flat so that we don't get more than 0.016" of rear trigger elevation. If this gets much above 0.016", the safety cannot be engaged. Try activating the safety with the trigger pulled all the way back and you will see what I mean. The safety is blocked by the rearward trigger position.
Since I had the 0.016" brass stock on hand, I also used a 1/8" x 1/4" piece under the single disconnector foot in front of the trigger. I bent up one end a bit to help me grab it with tweezers to slide it in place under the disconnector foot. The vertical lip was also used as an epoxy surface. This disconnector shim shortened up the reset by about 50%.
These two shims are normally held in place via the spring force on the trigger and the disconnector, but need to be tacked into place for when the gun is actually fired. I placed two drops of quick set two part epoxy on the back side of the rear trigger shim, bridging the top side of the shim and the painted metal trigger housing.
The epoxy needs to be on top, not under the bottom so that it does not add to the shim height. This methods holds well, but the shim can be "popped" off if desired. If you really, really wanted this very solid, you could rough up the epoxy points (brass top and adjacent painted surface) to provide more "grab", but that does not seem necessary. Likewise I also used one drop of epoxy off the "lip" end of the disconnector shim to hold it into place.
A strip of 12" x 0.5" x 0.016" brass stock is available on line from amazon.com. I got a piece for under $5 with free shipping. One 12" x 0.5" x 0.016" strip makes many, many shims.
One more DYI bit:
The stock trigger spring appears to be made of 0.047" music wire. A 86 foot spool of 0.033" music wire (A228) is available from
www.mcmaster.com for $3.50 plus ~ $5 shipping. A trigger spring takes about 2" of wire, so you can experiment with a bunch of different spring angles for next to nothing and get the trigger weight where you want it to be. The shank of a 1/8" drill bit makes a usable coil form. On one spring I got the weight too weak (2 lb.?) and the trigger would occasionally get "stuck" at full travel if you slowly, gently released the trigger. The trigger spring weight was not strong enough to overcome the disconnector spring force without modifying the disconnector spring. I did not want to do that. That was a whole $0.006 down the drain with only 85 feet, 10 inches of wire left to play with.
I went with a version with a wider leg "spread" and brought the trigger weight back up.
Use the stock trigger spring as a template when making your own spring. That includes leg length, number of turns (~ 1.4 turns) and leg spread angle. Using 0.033" music wire, the angle spread needs to be a bit larger than the stock spring (10 degrees?)
I am a newbie posting here, so I don't know how to get pictures up or know where to post a write up with pictures that I could point to from here. If I can figure that out, I will post more details.
With a smoothed up action, a 4 lb. pull trigger, and a much shorter trigger pull and reset, the rifle trigger starts to remind me of my CZ 75 SP-01 pistols. Much, much better.
Plus somewhere along the way the "trigger sting" seemed to go away as well.
The main thing about this change is that there are no permanent modifications to the trigger other than removing the trigger pack weld and smoothing up the action. At any time I could pop out the shims and replace the stock trigger spring if I was ever nuts enough to want to go back to a long, stiff trigger complete with "trigger sting".
I am very happy with the new trigger feel. Between the 2000 grit sandpaper for smoothing the trigger ($5 - Lowes's/Home Depot), the 0.016" brass strip ($5), and making my own custom trigger spring (~$9) I haven't really spent a lot of money but feel like I have added a lot of value.
- DanT, Phoenix, Az