A Nesika is a 105%, -5% type action. Simply to mean the striker is as cocked as its ever going to be when you raise the bolt handle. -That'll be relevant here in a sec...
To tear down a Nesika fire control, 1st, remove TWO set screws stacked on top of each other down inside the tapped hole located in the cocking piece. A .0625" allen key is the size. Next, shine a light down in the hole. You should see a drill point that interrupts the threads machined on the back end of the striker pin. Take notice of how it looks.
Now, unscrew the striker using an 11/32" or 8mm slim pattern type "ignition wrench" from Craftsman or wherever. When I do this I hold the shroud in my right hand with firm thumb pressure on the spring body. When it pops loose this will keep parts from shooting all over your blast radius.
So, now do your thing. Whatever that might be.
Reassembly. First, it sucks. Unless you have a fire control compression tool for assembly, it's just a bugger to do. I drilled a hole in the side of my bench large/deep enough to capture the front half of the striker collar. I palm to the shroud/cocking piece and place that just below my gut. Then lean in on it and deal with the thing trying to eat a hole through my hand. With the free hand, start turning clockwise to get the striker pin to engage the cocking piece. Use your mouth to tell anyone within a city block just how bad this part of the job sucks.
Once it bites:
I get a few revs deep, then I drop a .05" dia allen key into the hole where the two set screws go. I use my thumb to push down lightly as I screw it tight with the wrench. All I'm doing is "fishing" for the countersink that the set screws register into. Once I feel the little allen key fall into the pocket, I remove it and use a light to see down in there. It will time with another rev or so of rotation.
Now, just stack your set screws and your done. To compress the assembly for re installation into the bolt there's two choices: A Kleinhorst tool from Brownells or a .05" allen key stuck into the rearmost hole and leveraged into the small hole drilled at the back of the bolt shroud. That is why those two holes are there. Grease up your shroud threads with either moly or copper anti seize.
Nesika striker springs do not have a great deal of wall clearance from the inner bolt body ID. Use any lubrication very sparingly here. X10 if you use this thing in winter climates. It is worth your effort to find a lubricant that tolerates cold weather. If the stuff turns to peanut butter, you will have light strikes.
I ran Nesika's rifle production from 2003 to 2006.
Hope this helps.
C.
LRI