“Military Rifles” is a misleading term.
99% of hunting rifles in the world are based on Military rifle designs. The vast, vast majority of modern bolt-action hunting rifles use the Mauser design (used in the Mauser K98, standard arm of Germany in two World Wars), with those that are not based on the Mauser action using a derivative of the Lee-Enfield or Mosin-Nagant action. Most Lever Action rifles (Such as the Winchester Model 94) are based on lever action rifles used during the US Civil War and by the Army, Navy, and Cavalry during the Wild West era.
In short, almost any rifle is or was arguably a “military rifle” at some point in the design process.
The thing I’ve noticed is that people who hate guns tend to hate Shiny Black Tactical Guns. Show them a SMLE Mk III*, M1 Garand, or Mosin-Nagant M91/30, and they’ll say it’s “old junk”, but show them an AR-15 or AK-47 and they freak out. You’d think the AR-15 comes with a special attachment for puppy kicking and there’s a variant of the AK-47 that makes obscene gestures to kittens.
The AK-47 cops a lot of flak for being a “Commie Gun”- and remember, kids, anything to do with Communism is bad, M’kay?- and now that International Communism is no longer the threat it once was, the AK-47 is seen as a Terrorist Gun- ironically as a result of China and the Soviet Union supplying them to all and sundry in the '70s and '80s.
The M-16 has been held up by the Internet Gun Commando crowd as being the Epitome Of All That Is Right With Firearms, leading to negative connotations involving people in black tactical gear with tactical harness rigs at the range arguing over which Laser Sight to put on their Bushmaster, or what type of ammunition will make the biggest hole in their target.
The solution, of course, is for the semi-auto rifle shooter to get an L1A1 SLR or M-14- neither rifle being tained by connotations of Communism, Terrorism, or Internet Tactical Gunwankery.

As for Automatic Weapons- here’s the thing: A Machine Gun (say, a GPMG) has a rate of fire of approximately 600 rounds per minute, or rounds a second. Most MGs have a rate of fire in this region.
Ammunition is not all that cheap, really. The cost for centrefire ammunition in Australia hovers around AUD$1/round, depending on calibre (.223 and 6.5x55 Swedish are about 80c a round, .458 Weatherby can be as much as $3 a round, and .500 Holland & Holland is about $5-$10 a round, assuming you can even find the ammo). In short, even getting enough ammunition to fill the 250 round belt on a GPMG is going to be expensive. 250 rounds of ammunition is heavy. Really, really heavy. As in, too heavy for most non-specialist military people to effectively carry, along with the MG, and still be able to operate it all.
Personally, I think the NRA does more harm to the cause of legitimate firearms ownership than good, but I accept that’s a minority opinion not shared by many gun owners, least of all in the US.