The Firearm thread: Engineering artistry of wood, polymer and steel.

[Stealhead]

Originally Posted by Red October1984

Most AR's should be chambered for 5.56...

What kind of AR do you have? Yes there is a difference...but with AR's you never know. There are some AR's that are officially chambered .223 but are really rated for 5.56

When you are talking about an AR-15 it depends on when it was produced from the 70's into the early 90's they usually where chambered for .223.After the end of the Cold War there was a ton of mil spec 5.56mm laying and the many makers of AR-15 and clones decided that they should produce the rifles in 5.56mm instead.The date of manufacture makes a difference but the biggest thing is what is stamped on the weapon you should use that caliber even if there is a very very similar caliber.

I would not fire 5.56x45mm out of an AR-15 that has a .223 chamber even it does not explode which is likely a old gun shooting wives tall the two cartridges are different anyone that says other wise does not know what they are talking about.


The 5.56mm cartridge has a higher pressure higher than the design tolerances of the .223 chamber now any fire arm is going to be able to handle a higher pressure to some degree so would a .223 chamber explode from a 5.56mm cartridge I very highly doubt it.Will the higher pressure cause damage over time? Yes. How much it would depend greatly on many factors.Will the higher pressure cause screwy problems like blowing out primers? Yes


I would wait on the new upper better route to go any day of the week.You know for certain the upper is designed to a certain spec.Also I think that old lowers and new uppers are cool it is a new gun and an old gun all at the time.

I like the page about the Mosin-Nagant they got a little carried away though it does have a safety and a magazine.