"there is no way to make a semi reliable and consistant while maintaining the kind of accuracy that a precision bolt action rifle like the M40 achieves."
If you are talking about M14s I'll agree with you but the AR platform is different. The advantages are simple - Threaded collar over threaded collar barrel attachment, no bedding to perfect or go bad, no gas piston/op rod harmonics to be concerned with. Building a sub minute AR is as simple as buying good parts and screwing them together. Anyone can do it.
The real difference between a bolt gun and a semi is in trigger control. A bolt gun allows the shooter to milk the trigger, constantly improving the sight picture until the rifle fires. A gas gun requires the shooter to pull more quickly and follow through by pinning the trigger back while the gun recoils. Failure to do this will often lead to doubles as the rifle recoils away from the trigger finger, resets, then runs into the finger again on it's way back forward. This is often seen on gas guns with rather light triggers and inexperienced operators.
One has to remember that the gas guns will be issued to "designated marksmen" and that it will be perfect for this role. The Corps will retain the outstanding M40 for "precision" work.
There is so much more to accuracy than just "buying the parts and slapping them together." Yes, the AR platform has a lot of advantages but having owned, shot and worked on literally hundreds of examples, I know that while the AR platform is desirable, it isn't all that.
To get an AR to an acceptable level of performance, you need to match the lower and the upper receivers, This is a LOT more than just slapping them together. It involves fitting the pieces so that there is a minimum of play but enough flex to prevent problems. Then you need the proper torque on the barrel nut and the correct indexing. Next you need to ensure the proper gas tap in the barrel. Too much or too little get you accuracy problems. Next you need to put a match grade crown on the barrel. What comes from most sources leaves a lot to be desired. Now that the basics are down, you need to get a GOOD trigger. You need to make sure that the barrel has a match grade chamber and that the lug face is trued. The bolt face needs to be trued and the bolt carrier balanced. The gas key alignment has to be checked and verified and the recoil buffer matched to the bolt and buffer tube.
There is more to the process but you get the general idea. The point is this. I shoot a LOT of long range stuff. I have never run across an AR of any caliber that can match a bolt gun at 1000 yards or more. The key difference isn't trigger, or anything like that. It's consistancy of lock up on the bolt to the breech face. A bolt gun is repeatable every time due to the tolorances involved. A semi auto needs looser tolorances to allow for the action to operate. This degrades accuracy and consistancy.
I'm not knocking the USMC for going with this gun, I think it is a good midlevel platform. I just hope they understand how to employ a suppressed weapon like this to the fullest of it's ability. In all of my years training LEO and military, I've yet to see any with the knowledge to properly use a suppressed weapon. There aren't many guys out there who know how to do it and fewer still who offer training on that subject. Most of the good ones won't deal with the US Government.
Mike