With the iron sights in the prone position I'm competent out to about 400 yards. Standing brings that down to maybe 200-300 yards. In the right hands with a decent optic the gun can be shot accurately out much further. My eyesight makes the aft portion of the sight a little blurry. GF thinks it is time I got bifocals.
400 yards sounds about right from prone - optics dependent. 200-300 yards flat footed cannot be right. Are you sure that wasn't a typo?
Mostly I have shot sitting at a bench with the gun resting on shot bags but the small amount of standing shots I've taken were at about that range and I could hit a torso-sized target and a 3-ft x 3-ft metal plate slightly farther out. Not a group or anything just hits. I think I could hit a stationary man at about 200 if I wasn't worried about cover. I got a decoration for marksmanship in the service. I have 20-10 vision but am farsighted.
I got bifocals and I wouldn't waste my money on them again. I may be weird but:I never got used to that trying to make my eyes look down at the end of my nose or feet thing. 97% of the time it's easier to just take my glasses off to see the nearby range. I can't imagine how they would work in trying to view a rifle sight. I think contacts might be your best bet for that.(kinda funny writing this reminds me I used to make contacts before I started my career)
165 grains (308) vs 55 grains(223) http://www.hornady.com/assets/files/ballistics/2012CatalogCenterSpread.pdf It's all about the deliverable. How much energy are you delivering to the target? Look at the ballistics chart and tell me you want a .223 at 500 yards.......
I just wear granny reading glasses down on the end of my nose which doesn't work for shooting and doesn't work for flying either. My flying has tapered off to almost nothing because I can't properly see the instruments without the reading glasses. The seat doesn't go back far enough and I'm so far back that I don't have proper authority over the rudder pedals. Wearing my grannies makes any passengers pretty uncomfortable. In the words of Waldo Pepper, "never disconcert the masses". Alot of people are recommending a shotgun in this thread. I have a Rem 870 Tactical Magnum that shoots those big magnum 12 ga. shells. There was a raven that was literally tearing apart my patio furniture and tearing pieces of trim off of the main house (a big raven, maybe twice the size of a crow). One Saturday morning I heard it ripping a piece of wood trim off the roof drainage gutter, rolled out of bed and grabbed the 870 and walked outside. The raven flew off of the roof and onto a fence post about 30 feet away and I carefully aimed and fired at it (with a conventional 2.5" shell with light game load). The raven flew off and gave me an indignant squawk. Not even a single feather came off of the bird. A complete miss. I have got to be the world's worst shot with a shotgun. I even have one of those fancy glowing shotgun sights on the end of the barrel. I'm not sure a shotgun is all that effective without some training. I've simply never been taught how to use one and regular rifle technique does not work. Same for a pistol. I suck completely with a handgun because I've never been taught how to properly fire one. I compensate by owning very small caliber handguns that give me a chance. My .357 is almost useless in my hands unless I load .38 or .38+P in it.
Agreed the M1A is a better choice- IF- you are owning it for practical purposes. Sounds like the OP is wanting it more to make a statement, which the AR15 does. It makes a nice wall hanger, if that's your thing, but will likely never keep you warm under the blanket the way a good firearm will. I prefer a 12 ga pump shotgun myself. Buckshot can easily turn an unwanted intruder into wall paint. Slugs are accurate enough if I feel the need to kill at a distance. The semi-auto is likely superior shotgun, as FC mentioned, but I still prefer a Mossberg pump because they're reliable and require little maintenance.
Alot of good marksmen will use some pretty different techniques. One that works well for me, at least when shooting still targets is to take a full breath, then release half of it-then hold the last half while you aim and fire. It makes sense to me, because a) breathing causes motion (which some top marksmen prefer to have) and I am trying to make both myself and the gun still. b) holding your breath with full lungs can cause blood pressure to rise within the brain potentially tampering with vision and balance. c) if you hold your breath at the halfway point while inhaling, you will not have near the amount of oxygen in your brain that you will have when holding your breath after exhaling full lungs.
Your marksmanship skills remind me of my own. I wasn't any good with the puny civilian stuff . I was marksman with 45, sharpshooter with m-16 and expert with m-60 machine gun (think rambo first blood) and Tow missile. I guess I'd be considered an expert with the bayonet and knife but I'm hopeless with one where it really counts (in the kitchen). Guess I'll just have to live with the fact that if it comes to the zombie Apocalypse I'm toast because my 3 weapons of choice would be automatic shotgun, white phosphorous grenades and claymores. <iframe width="640" height="480" src="http://www.youtube.com/embed/p4ebtj1jR7c" frameborder="0" allowfullscreen></iframe>