Quoted:
I built an upper in 5.45 with a Bulgarian AK74 barrel.  It is an 11" shorty set up for full auto fun.  I used Model 1 Sales bolt with a CMMG M16 BC.  M1S bolts use a special over sized firing pin.  The tip of the pin is .077" in diameter and protrudes at minimum 50% farther then a standard 5.56mm firing pin.  I had no issues firing chambered cartridges of any of the following makes: Russian surp, Bulgarian surp, Wolf poly, and Silver Bear.  I did not install an extra power hammer spring.

Additionally I have built two 7.62x39 uppers , one 16" and one 11" with Bulgarian AK47 barrels.  These have M1S 7.62 bolts I drilled out to accept the M1S 5.45 firing pin.  I have used both of these uppers with no miss fires with this F/P set up and normal hammer springs.  I have used Yugo surplus, Wolf and Brown and Silver bear ammunition in these.

The C-Porduct 5.45 magazines are not satisfactory.  Almost every round feed off the right side jams on feeding, bolt completely behind the case head and bullet nose stuck firmly against the breach of the barrel at 10 o'clock.  The cartridges on the right are very floppy in the magazines with 1 or 30 rounds loaded.  I will try CProd 6.8 and USGI magazines next time out.

eta:

This picture shows from left to right:
-Stanard 5.56mm bolt and firing pin
-M1S 5.45mm bolt with their specific firing pin
-M1S 7.62mm bolt modified to take the M1S 5.45mm firing pin
-Colt 7.62mm bolt with the tail shortened to allow more protrusion with standard firing pin