by A-Poc

The AR-15 is basically a platform for assembling a rifle.  It is really versatile and can be a lot of fun.  The AR-15 in its simplest form consists of an “upper” and a “lower”.  The “upper” consists of the upper receiver with the bolt, the barrel, the gas block, the handguards, and any other items you add such as optics, handle, lighting, etc.  The “lower” consists of the lower receiver with the guts (trigger, safety, magazine catch, etc.), the handgrip, and the stock.

The AR-15 has two retention pins that hold the “upper” and “lower” together.  The cool thing is, you can make several different “uppers” to be interchangeable with one “lower”.  For example, you could make a .22 caliber “upper” for hunting small game, and a .30 caliber “upper” for hunting larger animals and just swap out the “lower” as you see fit.

The most common AR-15 configuration I usually see is with a 5.56x45mm NATO specific caliber “upper” (which is basically an M16).  This allows the user to fire either 5.56x45mm NATO rounds or .223 Remington rounds through it.  The .223 rounds have a little bit thinner brass and a little less chamber pressure.  If you build your “upper” to accept the 5.56x45mm rounds, then it should have no problem handling the .223 rounds.  The opposite is not necessarily the case.

Another important piece of information, is that the stripped lower receiver is the part you will have to have a background check for.  It is the part that is considered the “gun”.  As far as I know, everything else can be shipped straight to your door.

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{ 2 comments… read them below or add one }

Iota April 26, 2010 at 8:11 pm

It’s not true that you can swap a .308/7.62 nato upper on a standard ar-15 lower. The sizes are incompatible, the 308 round is too large to fit into the mag well of an ar-15. Now, you can get a 6.8 upper, a 7.62×39 upper, a pistol cartridge upper, or an upper in one of the more exotic large caliber rounds like the 50 Beowulf that will be compatible. But to fire 308 you need an ar-10 upper and lower.

jrokk May 2, 2011 at 12:44 pm

Iota is right

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