Can't somebody reload the 7.62x39mm to the equivalent of NATO specs, pick an OTM bullet for it in the appropiate weight and we are good to go? Why develop a new cartridge and weapon when you can just apply the technology available.

Is there a limitation that prevents this that I am not aware of? Can 7.62x39mm use 308 bullets?

No. Most rifles in 7.62 use a .311 bore. it is a low velocity cartridge, and wont fragment with any FMJ/OTM bullet at any speed. It also recoil heavily for its size, and the bullet has a poor BC.

Ruger rifles and US made ammo usually are .308, and you can safely interchange them. Safely, not always accurately.

DocGKR posted this over on TF in 2002:

The best performing 7.62 x 39 mm ammunition which we have tested is: Winchester 123 gr JSP (X76239): vel=2253 f/s, pen=14.4”, rd=0.56”, rw=90.1gr.

...Both the loads discussed above are older bullet design--with a new modern bonded bullet design, carbines in these calibers have the potential to exceed the effectiveness of .223 in CQB.

www.tacticalforums.com/cgi-bin/tacticalubb/ultimatebb.cgi?ubb=get_topic;f=1;t=000478#000000

Quoted: No. Most rifles in 7.62 use a .311 bore. it is a low velocity cartridge, and wont fragment with any FMJ/OTM bullet at any speed. It also recoil heavily for its size, and the bullet has a poor BC.

Read this. The Fackler tests were on old Russian ammo. The new ammo is different and some does indeed fragment:
www.tacticalforums.com/cgi-bin/tacticalubb/ultimatebb.cgi?ubb=get_topic;f=78;t=000521#000000

Robert, thats interesting. I didn't know that.

Also, making a magazine that fed properly in an AR would require milling the lower receiver to allow for the curve of the case.

ETA: There are some of those abortions out there with the AR mag welded to the AK mag. i hear they work.

Quoted: Can't somebody reload the 7.62x39mm to the equivalent of NATO specs, pick an OTM bullet for it in the appropiate weight and we are good to go? Why develop a new cartridge and weapon when you can just apply the technology available. Is there a limitation that prevents this that I am not aware of? Can 7.62x39mm use 308 bullets?

No..

7.62x39 = 30-30 for all practical purposes. TERRIBLE ballistics, TERRIBLE wound profile (no frag), and so on... The thing drops like a rock after 150m or so, effective range from a 16" bbl -> 200m max. And the tapered case doesn't help anything either... Add in some extra recoil, and it' sno wonder this cartridge has become obselete.

It is a TERRIBLE round, which is why the only places that use it for a first-line round are 3rd-world hellholes like Iraq & Egypt...

China: 5.8mm
Russia: 5.45mm
USA/NATO: 5.56mm

See a pattern?

BIGGER is NOT better, 5.56mm works fine in 77gr, so forget 30cal for anything that's not belt-fed or wearing a 10x scope...

5.56mm is the best all-around round available right now. As far as accuracy goes, all you need to do is count the number of 7.62mm weapons at your average hi-powe match (Around here it's usually no more than 3 - 95-98% of the competitors use 5.56)...  You can reach out to 1000m with the right loads, 500m with issue ammo... The 7.62x39 gets to 200m... Hmm, which would I want to have for an issue cartridge?

Not every battle is fought at 10m or less... This focus on carbines & point-shooting range has little application to the capabilities of an all-around military cartridge...

Quoted: Quoted: Can't somebody reload the 7.62x39mm to the equivalent of NATO specs, pick an OTM bullet for it in the appropiate weight and we are good to go? Why develop a new cartridge and weapon when you can just apply the technology available. Is there a limitation that prevents this that I am not aware of? Can 7.62x39mm use 308 bullets? No.. 7.62x39 = 30-30 for all practical purposes. TERRIBLE ballistics, TERRIBLE wound profile (no frag), and so on... The thing drops like a rock after 150m or so, effective range from a 16" bbl -> 200m max. And the tapered case doesn't help anything either... Add in some extra recoil, and it' sno wonder this cartridge has become obselete.

It ins't like 30-30 and a well placed round will drop a man with no problem.  I've shot lots of Eastern Block 7.62x39 in everything from bolt guns to AKs.  I simply find that none of it will group worth a damn.  If you can stay under 3xMOA, you are doing great.   Good quality 5.56 NATO is so wildly superior as to not be in the same league, but it isn't the answer for the third world.  7.62x39 out of an AK will work in horrible conditions in dirty junk $200 weapons.  

Someone made a comment that the bore on the Ruger Mini 30 is .308.  That isn't true today, but some of the old ones are.  I've shot a few cases of various brands of Eastern Block ammo through my Mini 30 and I can't get that thing to group in the same state.  I took it over to Newport NH (thirty minutes away) and talked to the boys in person.  They seem to think 4xMOA is okay.    It seems like such a great little package, but it simply doesn't work well.

Are you certain about the bore on the Ruger? My brothers 2002 rifle came with a warning in the manual that it had a .308 bore.