Some Christmas madness lull mythbusting...
My observations......
Standard Norc sks. mid 80's manuf. complete gun. dummy .223 carts...
A 223. will fit in the mag, 5 not very well.
The .223 will not chamber with the bolt fully closed, the shoulder of neck is higher than that of the x39's shoulder. The bolt would be unlocked and open about 3/8".
So if 1 .223 was inserted and the bolt was withdrawn to chamber it, A.. It would not, the rim is not big enough to depress the follower for the hold open device if inserted to the left side of the mag, the right side it will pop out. B.. If it did get released the round might be cocked at an angle and will jam the action. and or-
I found the following if many cartridges were inserted, A.. The bolt may strip more than one cartridge at a time, B.. The round may just pop out of the action and not chamber at all(I found this if the round inserted lay on the follower to the right side of the mag with more or less than full, I suspect since the .223 is smaller in dia. to the x39.).
So someone might have had the gun fire at one point time... by some part of the bolt coming in contact with the primer when cycled and detonating it(ex. a partly open bolt slamfire, or I guess if the round was fully drivin into the chamber and came to full lock up, to be able to fire... I could not reproduce nor was going to try.)
... for the most part not by pulling the trigger....
That being said, with many other rifles with conversions to/from .223/5.56 and 7.62x39, an sks with this caliber would be cool, not mention if it had a AR type magazine magwell and acceptability (wow a full 10 rnds finally with LAR mags )