The problem with the AR is the Johnson/Stoner bolt design that has too many lugs and a bad extractor design. The forces are not equally distributed on the bolt lugs, and they can break. The extractor springs weaken with use, and they fail to extract. The spring loaded plunger loses force, and it fails to eject during full auto. The gas port on the AR-15 does not have a way to constrict the amount of gas that enters the system, which is a problem when gas port erosion causes the gases to travel faster and faster into the gas tube with age and use, causing very high rates of fire, which causes parts breakage and failure.

Back on topic, the SCAR looks like it has an equally poorly designed bolt, which again fails to equally distribute the recoil forces on the lugs, but at least the ejector plunger isn’t in a place that will weaken a major lug, and the extractor looks a little beefier. That carrier is probably made as large as it is in order to reduce the rate of fire and to increase the inertia necessary to close the action when it gets dirty or fouled.

and i have to say that that bolt face comparison just did a lot to sour me on the SCAR. the ridiculous locking lug / barrel extension part of the AR-15 is its most unappealing aspect to me, and i wish FN had decided against copying it.

http://www.militaryphotos.net/forums/showthread.php?t=157086&highlight=scar

I don’t think you understand the difference between bolt and bolt carrier. In an AR DI the bolt is the piston. In an AK it has an overhead piston that is attached to the bolt carrier.

This is an AR15 bolt. It is also act as a piston.
http://www.bravocompanyusa.com/BCM-AR15-Bolt-Assembly-MPI-p/bcm%20bolt%20assemly%20mp.htm

This is the AR15 bolt carrier.
http://www.bravocompanyusa.com/BCM-Bolt-Carrier-Auto-M16-p/bcm%20carrier%20stripped.htm

Combine the two it is called Bolt Carrier Group.
http://www.bravocompanyusa.com/BCM-Bolt-Carrier-Group-MPI-Auto-M16-p/bcm%20bolt%20carrier%20group%20auto%20mp.htm

The AR15 DI action is simpler then any overhead piston design like the AK or SCAR because the piston is part of the bolt. In an AR15 DI everything is in one nice compact package.

Carl the SCAR is an overhead piston design hence the BCG will be big and heavy.

No, he eliminated the piston in the design for his lightweight surivival rifle. For a general use military rifle it made for a very dirty, unreliable design.

Between that, the lack of an articulated plunger ejector, and no gas rings on the bolt, I’m pretty sure that the core AK operating system has fewer parts than the core AR operating system.

Any time they swtich from metal to plastic is a step backwards in my opinion.

Check out the AR15 link.

Mechanically, any overhead piston design will have more parts then DI AR15. Stoner made the piston part of the bolt. What this does is increase accuracy, made it easy to manufacture, and lighter.

If you like I can explain how an DI AR15 action work. It’s very simple but most people don’t understand it.

From what is see able from the pictures, is the SCAR simpler, or would it be less prone to jamming, etc?

I had the opportunity to see one of the so-called “gold” blemish models up close at a local show recently, and it didn’t change my opinion any. Gun’s still ugly.