I'm looking for a lightweight carbine for my first AR. The weight of an AR is very important to me. If I wanted an 8 pound carbine, I'd get a .308, you know what I mean?

Well, while perusing the catalogs of the various manufacturers I've noticed something odd: Why is it that Bushmaster or Colt can build an M-4gery that weighs 5.5-6.5 pounds and RRA and Armalite can't seem to build anything that weighs less than 7.5 pounds?

Are they using different methods to weigh (with or without full mag), or are they really that much heavier? Why?

Did you check on barrel profiles?  HBARS would weigh a little more, I'd think.

Other than that, I dunno.

Quoted: I'm looking for a lightweight carbine for my first AR. The weight of an AR is very important to me. If I wanted an 8 pound carbine, I'd get a .308, you know what I mean? Well, while perusing the catalogs of the various manufacturers I've noticed something odd: Why is it that Bushmaster or Colt can build an M-4gery that weighs 5.5-6.5 pounds and RRA and Armalite can't seem to build anything that weighs less than 7.5 pounds? Are they using different methods to weigh (with or without full mag), or are they really that much heavier? Why?

Barrel contour. Bushmaster, Colt, and Olympic Arms offer lightweight thin profile barrels.

Ah, I figured it was probably the barrel, I should have said that in my post.

I just don't understand why anyone would want to carry 2 extra pounds of barrel on a carbine? It's not like it's a varminter or match rifle...

Quoted: Ah, I figured it was probably the barrel, I should have said that in my post. I just don't understand why anyone would want to carry 2 extra pounds of barrel on a carbine? It's not like it's a varminter or match rifle...

Some people do those carbine courses/matches.  My understanding is that the heavy barrel helps with making quicker follow-up shots.  (In CQB type courses, ect.)