Picture this one, guys...
You buy a kit... say a '74 in 5.45. you screw the front trunnion.
You buy a 7.62 barrel, bolt, and trunnion, which is drilled and tapped.
You buy a 5.56 barrel, bolt, and trunnion, and drill and tap that.
could you interchange without too much hassle on one receiver, just by unscrewing the trunnion bolts, and changing barrels? Stupid Idea?
Hmmmmm, Maybe I need to bring that up to Meeper, since the Beowulf RPK would be using 5.56 mags anyway, Galil to be specific. Maybe I could interchange 5.56 and .50 cal barrels.....That would be BAD ASS.
I've thought about the same thing - a bolt-change caliber conversion
I've done some reading on this for some time and there are actually two 5.56 versions floating around out there. Problem is, as I recall, is that no "official" 5.56 caliber was created, only by aftermarket factories like Norinco. So watch it with the trunions.
As I recall, the Chinese 5.56 version uses a 7.62 sized bolt and trunion, and all parts except the bolt would interchange w/ any other Chinese 7.62 part.
THe other caliber is that from the Romanian / Euro factories and I think those are the ones that use the 5.45 bolt/trunion.
SOOOO... you couldn't use a Bulgy/Romy bolt in a Chinese rifle, and vise versa. I think there's even a 3rd pattern but don't remember at all.
I'm going to build one from the ground-up and use all Euro parts (probably from K-Var).
Again, I'm doing this from memory and never bookmarked those threads. Check the gunsnet Norinco forums. There's more about how magazines interchange than anything else, but there are some discussions about the bolts.
As far as the receiver, you could enlarge the rec to accomodate any mag, since the mag well dimples keep it in place. Don't see any problem with that.
The only differences between the norinco .223 and the 7.62 appear to be a different bolt as you say with the same carrier (so you could swap bolts). The outer bolt diameter also appears to be consistent. Further, as you say, polytec made its own .223 version so I can't comment on that, what I can add though is that norinco, polytec and SARs all use different mags.
With the SAR-3 5.56 AK, the parts that are specific to that weapon and not found on any other AK are the gas block, the bolt carrier, the bolt assembly, and the hammer. Have not a clue why they changed so many things from standard AKM/AK-74 design.