1 to 2 inch groups at 100 yards is excellent accuracy on average. Combat accuracy is usually 4 to 6 inches at 100 yards. And your right stone, the tighter the groups, the tighter the weapon tolerances. That's why the AK-47 will still run with sand, mud and crap in the action but shoots about 6 to 8 inch accuracy. At the opposite end is the M-16 family of weapons which shoot 2 to 4 inch accuracy but must be kept meticulously clean in order to function properly.
As to power, I'll take the .30-06, .308/7.62 NATO or .30-30 round in a bolt action. For a lever action, again the venerable .30-30 round is about all you would need. If I have a lever gun in .45 Colt or .357 Mag and a matching pistol, I would not feel out gunned in a fight. Easier to carry the same ammo for two weapons than seperate ammo for each. That is the reason that a bolt action or lever action rifle is best for a SHTF gun. (Hint: Since the .357 Mag weapons also shoot .38 Spl, you're actually getting 4 weapons for the price of 2.)
Most semi-autos are very intolerant of pressure variations of various manufactured ammo. The M1 Garand is a good example. Loaded with M2 ball or other military surplus ammo, it works great. Shooting civilian ammo in it will ruin the weapon as the pressure curve is sharper and can bend the operating rod. The most forgiving semi-auto rifle that I've found, pressure wise, the the little .30 M1 Carbine. That short-stroke gas piston action seems to work well across a broad spectrum of pressures. .
JMHO. YOMV.
