I have had all three calibers and now I only have the 5.56 and 5.45. I think that in the AK platform, the 5.45 is the best choice for range shooting, which is all that most people will ever do with an AK. In a different platform, everything below would be different but we are only talking AKs.
- 7.62 is obviously the most popular AK and is easy to find ammo for but for me, I was just punching paper and I got a little tired of the recoil. Now, granted it is not bad recoil but it is significantly more than the other 2 and more than I wanted for just shooting at the range. I have kids and a wife who like to shoot, I'm not going to risk putting them off of shooting because their shoulder hurts afterwards.
- 5.56 is a great round and I have not had any issues with reliability out of my converted Saiga. Mags are a little difficult to find but it's not that bad and besides, it's not like you need to buy them on a daily basis. Grab a few when you see them and then grab a couple more later. I also have ARs so I have the ammo anyway, so that is the only reason I still have one 5.56 AK rifle and I don't really shoot it that much.
- 5.45 is also a great round and very inexpensive to shoot. I don't hold with the idea that the ammo will eventually get hard to find. This caliber is standard issue for one of the largest militarys in the world, so it's not going away and Russia definitely needs the money. Once the surplus dries up, if it does, then companies like Wolf, Bear and Tula will step up production like they have with the 7.62x39. This is my favorite round to shoot just for simple economics and the performance out of an AK is every bit as good as the performance of 5.56 out of an AK. Notice I said "out of an AK", out of other rifles, the 5.56 is hands down the winner, but we are only talking AKs. The cost of mags is more than the 7.62 mags and about the same to a little more than the 5.56 mags but that cost is made up after shooting just one full magazine of ammo.
Speaking of cost, the 5.45 has the others beat by a mile. Current 5.56 averages around $0.50 per round ($15 per loaded mag). Yes, I know you can catch it on sale or buy it in bulk and get it cheaper, but I think I am a pretty typical shooter and I can't throw down $400-450 to buy a 1000 round case and I end up having to buy it in much smaller quantities, which means I pay 50-60 cents per round. 7.62x39 averages around 30 cents per round or $9 per loaded mag. 5.45 averages around 20 cents per round or $6 per loaded mag.
It is going to take me the same amount of time at the range to run through that 30 round mag. In less than 2 minutes (usually less than 1 minute) I'm spending $6 for 5.45 or I'm spending $15 for 5.56, the decision is pretty clear to me because at the end of the day, that paper target is just as dead.
I always think in terms of what might be available as "pickup" ammo. For that reason, I'd love to have a 5.56 modded to take AR mags. Personally, I like the 7.62 platform I have, but I'd like the ability to use the plentiful AR mags and ammo that may be around if things go toes up.
If you're looking for a cheap weapon, go for a 5.45 rifle. If not, go for a 5.56 AK with the Definitive Arms AR magwell. With that you get the best rifle performance and the best ammo performance combined, plus relatively inexpensive mags (compared to reliable and durable AK mags, let alone 5.56 mags). Only setback is that the whole setup will cost around two grand