Dear Bob:
I've had some interesting experiences with my Yugo SKS I'd like to share.
By the way, I'm pretty sure my Yugo SKS was unfired like you said yours was.
I've had cycling problems during the first (post cosmolene removal) box of Russian rounds which I believe I then cured via enlarging the barrel by-pass hole to a diameter half way toward that of a Norinco SKS I used to have. FYI, the by-pass hole diameter in my Romanian AD-47 is REALLY LARGE, way larger than that Norinco SKS's. I can give you the drill sizes/hole diameters I'm talking about if you wish.
During the next 40 rounds or so, my firing pin stuck due to the metal forward of the fp retaining pin, metal on the fp itself, literally plowing up (upsetting) and locking the fp hard in a position of lightly denting some or most primers. I found this was not a dirt fouling issue, rather actual upset/shearing forward of the fp metal, thus dragging on the passage way in which the fp fits. One would think the fp would be very hard, and would dent the retainer, but no. I easily filed away the upset metal on the fp with a regular file, but I've not used that original fp since. It's a wonder the SKS didn't go auto on me as the fp tip was protruding out of the bolt about as far as a regular fire-travel. The gun actually fired singly, after reloading the lightly dented round. Sometimes I'd only get a "click" though. I had to drive the fp out of the bolt with a drift punch with pretty good hammer effort.
Thanks to you and Brownells, I now have a Murray fp and it works well. However, I'm not thrilled with the shape of the Murray unit, as I feel the original fp design has a broader tip, other than the possible hardness issue that caused the metal upset problem. I'm not convinced Murray's spring idea is needed or worth the trouble. AK's don't have a spring, nor did my well-working Norinco SKS.
To go on, again, now I'm getting that primer-punching protruding metal ring on the bolt face I read about. I've filed that down (with another diamond file), but now wonder if the Yugo people didn't heat treat the bolt correctly. It seems to rebuild itself in about 40 rounds of fire. I believe the bullet bases are actually extruding the folt face. And, maybe Murrany's fp design is contributing. I'll be looking for another bolt at gun shows, or trying one from Numerich or someplace. Maybe the new one will be from another country and be harder. I believe all SKS bolts, whatever the country of origin, are the same design and size.
Lastly, I installed a 30-round magazine which works very well. It is a "USA Mag" unit, which, contrary to your comment, DOES hold the bolt open nicely when empty. What make did you try?
Interestingly enough, none of my AK mags held the bolt open until I found a Yugo AK mag. which does. As a sidelight, somebody showed my how to modify non-holding mags via disassemble and reworking to hold a bolt open.
That's all for now.
I'd like to hear if you got this note and if you think I'm on the right track with any of my Yugo SKS comments, etc.
Ps, my next move is to try a buffer. Numerich has them for $9.95, but I'll look at gun shows first. Think I'll get one for my AK, and maybe my Smith and Wesson .22 caliber model 41 target pistol too.
Don of Milford (Cincinnati) Ohio.