Ok, I have a little more time now to answer your questions.
First of all, let me begin by saying that I own four rifles chambered in 7.62x39 and I have been shooting it for years. I bought my first SKS back in the early 1980s and shortly thereafter I bought an AK style rifle in 7.62x39. Currently I own a Russian SKS, a underfolder AK type rifle that I put together from a parts kit on a new receiver, a fixed stock AK style rifle, and a registered SBR Krinkov in 7.62x39. So I am not unfamiliar with the cartridge.
I shoot a lot by most people's standards and I have been doing that since I was a kid. I probably shoot on average four times a week. And to be honest, I sort of get bored with the same old thing. Bored might not be the right word. Maybe it's better to say that I like to try new things.
I have known about the .300 Whisper cartridge almost since it started. The guy who came up with it, JD Jones of SSK Industries lives about 10 miles from where I grew up. When I was a kid, he was a member of the same sportsmans club as my dad. And I grew up seeing him shooting a lot of his creations out at the club and hearing (usually second hand) about the stuff he was working on. Including the .300 Whisper. Obviously, years later, the .300 AAC Blackout became mainstream and it got a lot of discussion by a lot of people. And, I always thought it was something I thought was interesting and something I intended to try at some point. I got started in .300 Whisper about a year or so ago when I took a Remington 788 rifle, originally chambered in .223 Remington to SSK and had it rebarreled to .300 Whisper. Right off the bat, I really enjoyed it; for a number of reasons that I will get into later. I had so much fun with it, I ended up buying the Ruger American in .300 AAC Blackout.
When we talk about one cartridge "kicking some other cartridges butt", a number of factors come into play. First of all, there will always be another cartridge bigger and faster than whatever cartridge you are talking about. You say the 7.62x39 kicks the .300 AAC Blackout's butt. Ok, if you consider typically less than 100 fps more velocity being a butt kicking, OK. But if that really matters then the .308 Winchester kicks the 7.62x39's butt and the .300 Winchester Magnum kicks the .308s butt and so on. The question you have to ask yourself is: does this do anything meaningful or useful for me as the end user. In my case, it doesn't. Again, I shoot paper and I shoot steel. Having an extra 80 fps muzzle velocity does nothing for me. Yeah, it might shoot a little bit flatter at long range but if I know my dope, I simply had another click or two of elevation to the scope and I am there.
Magazines: I have easily put a thousand rounds through my Ruger American and the two magazines I have work fine. Yes, the first time or two I took them out they had a tendency to hang up on the first round out of the mag. I used them a little bit and the problem went away. My magazines hold six rounds. I shoot paper and steel. Having a 20 round not only doesn't add anything to my enjoyment of the rifle, it actually detracts from it because I am shooting mostly from the bench. I don't need 20 rounds in the gun. And the longer mag sticking out the bottom of the gun gets in the way of what I am doing with the rifle.
Cost of ammo. Like anybody, I wish ammo was cheaper. Hell, I wish ammo was free. But, for the majority of rifle shooting I enjoy, I don't go out of my way to find the cheapest possible thing to shoot. I reload all the ammo I shoot and when I am shooting a rifle, I am almost always shooting a fairly premium bullet. I am not trying to see how cheap I can shoot, I am trying to see how I can achieve the best possible accuracy. In my subsonic .300 Blackout loads, I am using 220 grain Sierra MatchKing bullets. Not the cheapest possible option. In supersonic bullets, my go to load is the 125 grain Sierra Tipped MatchKing. Again, not the cheapest option but one that seems to shoot the best in my gun. As I mentioned, I am currently playing with G9 bullets which are a super premium bullet. If I was looking for a cheaper .300 AAC Blackout ammo to plink with, I have tried two different coated, cast bullets. I played around with them using a few different powders and loads: they shot OK and if I was plinking they would work fine. They are FAR cheaper than the jacketed bullets I typically use. However, for what I do: shooting groups on paper and shooting steel at longer ranges, those cast bullets just didn't shoot good enough (for me) to be interesting. When Townsend Whelen said that only accurate rifles are interesting, he echoed my sentiments. Don't get me wrong, I do plink. I love plinking. But with this particular rifle, I am much more into shooting tight groups.
Bullets: The .308 diameter bullet may give a reloader the single biggest selection of bullets of any caliber out there. From 80 some grain bullets, on up and beyond 220 grain bullets. In addition, I load for the .308 Winchester and .30-06 so I have done a lot of work in .300 Blackout using bullets I had on hand. So the .308 diameter bullet makes a lot of sense for me. FWIW: I don't load 7.62x39. I have shot a fair bit of 7.62x39 ammo over the years, but it has always been surplus or low end ammo.
Powder: the .300 AAC Blackout uses the same powders as magnum revolver cartridges. The first time I opened a reloading manual to prepare to load .300 Whisper, I realized that I already had every single powder they listed for the caliber because for years I was into shooting .44 Magnum and .45 Colt handguns. Again, for me, this was a nice bonus.
The reloading process itself to me is very interesting and very rewarding. This is a hobby within a hobby. And I enjoy that aspect of the hobby almost as much as shooting itself. The .300 AAC Blackout has provided me with lots of stuff to play with. I mentioned the thing about the subsonics in passing but the point of me playing with them is that it taught me a lot about loading precision ammo. I have been reloading for decades, but achieving really good results with subsonics in .300 Blackout taught me a lot about precision reloading. I was not just stuffing powder and bullets in a case trying to produce cheap ammo: doing that doesn't work with subsonics past 50 yards. It required me doing a lot of research on how to lower my standard of deviation, keep very low extreme spreads, concentricity................ It was a great learning experience and with that knowledge I gained loading those subsonics it is now something that I use to produce much better quality ammo in my other rifles.
I have nothing against plinking. I have done a whole lot of it myself. I would hate to even guess how much ammo I have put down range, plinking. But I have guns that I use for plinking and this Blackout isn't one of them. And again, I am into shooting tight groups on paper and shooting steel at long range. So cheap/bulk ammo isn't something I am interested in for this rifle. In other guns I own and use for other purposes: that may be the main thing I am interested in.
Again, there are hundreds if not thousands of cartridges available to American shooters, and new ones are being developed every day. There are hundreds if not thousands of guns available to American shooters out there. And one reason for this is that different people have different interests in the shooting sports. What pulls your chain may not pull my chain. What you think is the do all and end all of guns or cartridges may not mean a thing to me; my idea of the do all and end all might be totally different either just because of personal preference or because we are using the guns for totally different things. And that is OK. There is nothing wrong with that. One of us is not right and the other wrong. The important thing is that we, as Americans, have those choices available to us and we have the luxury of living in a country where we can enjoy ourselves in the way we see fit.
