Remington, and sibling Bushmaster, have announced a new cartridge designed for the AR-15. The 30 Remington AR is a .30 caliber cartridge the length of a .223, allowing it to be chambered in AR-15s rather than AR-10 style rifles.

John Snow has the details:

The big difference is in energy. The .30 RAR in this bullet weight has about 500 ft-lb. less of energy than the 165-gr. .308 at any distance. A substantial amount less and one that will certainly have an effect on game in the field—but how much of a difference we’ll just have to see once we start killing some deer with it.

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The R-15 is said to weight about 7.5 pounds, a full pound less than the R-25 in .308 Win.

More info @ Gun Shots

UPDATE: tammons @ ar15.com came up with this diagram of the case:

Short and stubby. It reminds me of the 7.62×39 as some have said in the comments. Oh and lets not forget the .30 Steve.

The consensus seems to be that it is a cut down .284 Winchester case, as is the .450 Bushmaster.

Yep looks like a short 284 case.
Good. I am glad somebody is doing this.

Should be a great hunting round, but hopefully they will be slow twist for less pressure like 1:16 – 1:18 twist etc.

Its sort of a AR15 version of a fatter 30BR. The 30BR case is 1.51″ L, the 30 RAR is 1.53″L.

A 30 br with a 22-24″ barrel can push a 125 gr moly bullet to 3000 fps with 34.5gr of H4198. I had one for a while and they are nice.

I doubt they will be able to run it at 55-60k unless they use an oly wssm upper and bolt.

For benchrest nothing is going to beat a BIB 118 gr bullet in a slow twist barrel
This should be a really good round if they do it right.
Look at some of the groups on the link below.

Here is a good read on the 30BR if interested

http://www.6mmbr.com/30BR.html

I had actually already designed something similar, a longer case version a while back just playing around.
I have a couple of 284 based bolt rifles, one straight the other 338/284 and its a good case. Very efficient case.

I ran it through case designer and modified it to a 30 RAR and the case should hold right at 43-45 gr h2o.

Its a short stubby little bastard.

The case capacity is just slightly more than the 30 BR but you cant hang the bullets out like a bolt rifle.

UPDATE: The GunPundit (Murdoc) says it will uses .450 Bushmaster magazines. Presumably single stack.

A couple of comments have asked how it stack up against the 7.62x39mm and if there is any need for such a cartridge.

How does it compare to a 7.62×39?

The 7.62×39 FMJ 123 gr round leaves the barrel at 2,300 ft/s with 1480 ft/lbs of energy. The 123 gr .30 RAR will leave the barrel at 2800 ft/s and generate 2141 ft/lbs. That a 30% increase in muzzle energy. This is a significant increase in a hunting situation.

This splits the difference between a 7.62x39mm and a 7.62x51mm (.308 Win.).

If the round uses .308 projectiles there will be a very wide variety available to the hand loader. Much more than is available for the 7.62x39mm (.310 projectile).

UPDATE: The outdoor wire has more info and this photo:

Left: .30 RAR, middle: .223, right: .308 Win.

The new shell will be available in three initial loadings: AccuTip BT, Core-Lokt PSP and a UMC MC the company describes as the “practice ammunition” for the hunter or shooter who doesn’t want the hunting round characteristics – or price. The two hunting rounds are 125 grain bullets; the full-metal rounds are 123 grain. Pricing is currently listed at $35.99 for the AccuTip, $26.49 for the Core-Lokt, and $18.99 for the FMJ.