Davek1977:
Over at SKSboards, Mr. Ben Murray (Murray's gunsmithing) answered these same questions about possible popped primers' causes.
His experience also indicates that different nations' production of SKS rifles results in varying amounts of free space, between the bullet and leade.
Even with nice smooth firing pin points it happens.
One of my SKS is returning from Murray's. They perform chamber reaming for $30, and none of those rifles ever had any more popped primers, with any sort of 7x39 ammo.
The chamber reaming prevents excess case pressure as the bullet then has enough free space. Tula ammo is one of the main factors in popped primers.
I bought recently bought 3,000 rds. of Tula, and then two very nice Yugo M59 rifles. A 59 is Not a 59/66.
javjacob: You might enjoy the improved sight distance and accuracy of the TS 200 aperture, from Tech Sights (website).