Well, let's start with basics.
There are three types of AK receivers, ones made from forged and milled steel, ones that are made from sheet metal stampings, and ones that are made with heavier gauge reinforced stampings.
You'll hear terms like milled, stamped, and RPK type receivers, which correspond to the three types.
Milled receivers are correctly AK-47's, stamped receivers would be an AKM or AK-74. Reinforced stamped receivers would be known as RPK or Yugoslavian type.
All three work fine, but it's much more important with a stamped receiver that it's done "right".
Stamped receivers are much, much less expensive to manufacture. Milled receivers just scream quality and they tend to provide a more stable platform and are generally more accurate. The reinforced stamped receivers are thicker than a standard stamped receiver, and they use oversized reinforced trunnions that hold the barrel into the receiver. These are also called RPK receivers since they were developed for use with the Soviet squad auto, called the RPK.
Stamped receivers are the most versatile when it comes to playing around with different stocks. Milled receivers are a little more restricted when it comes to that.
Milled receivers can be identified by two milled out sections on either side of the receiver right above the mag well. These are just lightening cuts for the receiver, although they may help in making the receiver stiffer.
Stamped receivers, with two exceptions, should have two dimples, again, one on either side of the receiver above the mag well. They serve as magazine guides when reloading the weapon. The two exceptions are the Century Arms imported Romanian WASR-10 series, and the Russian SAIGA, although current SAIGA's might be coming in with the dimples. Stamped receivers can also be identified by the rivets that hold the front trunnion into the receiver.
RPK receivers are what the Yugoslavians use. They are 1.5mm thick stampings rather than the traditional 1mm, and the piece that holds the barrel to the receiver, the front trunnion, is oversized and reinforced, so they are very durable, stable receivers.
There are three main cailibers available in AK's.....
The original caliber is the 7.62x39mm, roughly equivalent to a .30-30 WCF in power. This is a "pure" assault rifle round, with a tapered case designed to make it easy to get into and out of a chamber quickly and easily. It is also the least accurate of the cartridges available for an AK, but it's by far the most prevalent cailber.
The 5.45x39mm was introduced in 1974 with the AK-74, it was the Soviet's attempt at the lightweight rifle/caliber concept. They saw the M16 being used in Vietnam and they wanted a round that was similar. The 5.45mm has less recoil and greater accuracy than the 7.62x39mm round, and is a lot of fun to shoot. The rounds also weigh less.
AK's can now also be had in 5.56x45mm. You know all about that round, but what's important to remember with AK's in this caliber is there were never any attempts to standardize parts or magazines among AK producing countries....they were always export rifles and the Warsaw Pact fell before they were widely available. If you get a rifle in this caliber, stock up on magazines and parts specific to the rifle you have. You can find Bulgarian, Chinese and Romanian stamped 5.56mm AK's, and milled receiver Bulgarian AK's, which are being issued in Columbia and are replacing other AK's in Bulgarian service now that Bulgaria is a junior member of NATO.
You'll also hear about pre-ban, post-ban, and no-ban rifles. For AK's, the first ban was in 1989, when Bush Sr. banned import of foreign made rifles by executive order. Prior to that, the Chinese, Egyptians, Hungarians and Yugoslavians imported AK's. The Israelis and Finns imported high end rifles based on the AK action, Galils and Valmets respectively.
There were rifles imported after 1989 that had thumbhole stocks, no muzzle brakes, no bayonet lugs, etc. These were the beginning of the post ban rifles. Then in 1994, the Crime Bill came.
Post ban imports came from Romania, Bulgaria, Eqypt, China, Hungary, and Russia. These would then have to be "unbanned" to have all the evil features that most of us want.
The end of the Crime Bill allowed domestic manufacture of rifles with evil features. You'll hear terms like "parts count". Parts count refers to the # of US parts in a foreign made rifle that allow it to then have evil features. If you have 10 or fewer foreign parts in the rifle, and ATF has a specific list of what you can replace, you can have a rifle with a bayonet lug, folding stock, threaded muzzle, etc.
Without a doubt, Arsenal Inc. makes the best AK out there, hands down. I've been shooting, buying, selling and collecting AK's for almost 20 years, and these guys build an AK better than anyone. They set up operations in the US, and as subsidiaries of Arsenal Bulgaria, they sent technicians and gunsmiths over from Bulgaria and Russia to build AK's here on modern CNC machinery with the original blue prints.
As to what to buy......think about how much you want to spend.
Pre-1989 imported rifles will still bring a premium. They don't have to worry about "parts counts" and they are the least molested, so collectors will pay top dollar for them.
Top of the line milled receiver AK's can go up to and over $1200.00. Some can be had for under $800.00. Again, another plug for Arsenal Inc. There are also Chinese milled receiver rifles out there, the pre-89 Polytech Legends, and there are post ban MAK-91's that are milled. There are also two types of Bulgarian post bans that were imported before Arsenal Inc. was set up, the SA-93 and the SLR-95. They can be had for around $500 or less and can be unbanned into some really nice rifles. The Bulgarian rifles use cold hammer forged barrels, extremely high quality.
Stamped receiver rifles are much more varied. Imported stamped receivers are typically the most desired. They aren't reverse engineered. Geometry and proper heat treatment of a stamped receiver are very important. It may sound like a simple thing to make a stamped receiver, but there really aren't any US receivers that are truely "in spec"....think about all the ruckus that the term "mil-spec" brings up when discussing AR's. Foreign stamped receivers are "mil-spec".
There are some well done domestic stamped receivers.....the ones offered my DCI/NODAK are the best, with Amory USA being very good as well.
Try to avoid Hesse, Vulcan, or early Ewbanks receivers. ITM/Ohio Ordnance have been around for a while, but they would be way, way, way down on my list of domestic receivers that are still acceptable.
A quality stamped receiver rifle can be had for $700.00 or less. The better rifles are actually "kit" rifles that were built from surplus rifles cut up as parts kits and then reassembled as complete rifles on new semi auto receivers with the proper # of US parts.
You'll want to know who built these up. Atlantic Arms offers some rifles built by Vector and Red Jacket that have a good track record. Armory USA/Arsenal USA have built many great rifles, although they went through a rough spot a while back. Current SA-85B's should be decent rifles.
Again, avoid Hesse/Vulcan, and some Ohio Rapidfire builds are worse than others.
Century imported a lot of rifles from Egypt and Romania, and they are now offering Yugoslavian kit rifles built on the excellent DCI receivers.
Century is VERY much hit and miss. You'll really want to inspect the rifle before buying, looking for canted front sights, bad triggers, and just overall quality.
Bear in mind that Century tries to sell a lot of rifles for a decent price, while they bring arms to the masses, sometimes quality suffers.
The WASR-10 is the cheapest, most prevalent AK out there right now. They are imported with a receiver that can't take military magazines, but Century then opens the magazine well to accept military mags. Some are quitre serviceable and represent a good value, but many have cosmetic issues and sights that aren't alligned properly.
AK's have a bad reputation, mostly unearned, for poor accuracy. They will never be bench rest rifles, but in terms of practical accuracy, they'll hang right in there with an AR with iron sights. I'm talking about unsupported real life shooting.
What's hurt the reputation in terms of accuracy for the AK is that people tend to buy the cheapest AK they can get and stuff the cheapest ammo they can find into it, and then want to compare it to their favorite AR.
I've beat guys in practical rifle competition using my iron sighted AK against their optically sighted AR.....
I know that this is a lot of information, and I've skimmed over a lot of issues.
Ask away on specific stuff.....there's a lot of knowledge on the board here, and you might also want to check out www.akforum.net
, lots of very knowledgeable AK guys there.
I'm sure I've missed alot of stuff so chime in with any info!