In what way are the RRA bolt groups "enhanced"?  

Are they heavier?  What is the weight of these compared to a standard GI bolt group.  Does anyone know the weight comparisons of the LMT group, the Young/Les Baer group, and these?

The RRA has less cutout in the rear, and has the extended firing pin ramp making it heavier (which is good).  The bolt itself is only "enhanced" becuase they now use heavy duty extractor springs in them.  The LMT is fantastic, better quality than the RRA IMO, and if it has the same features as the M16 unit - it has special qualities such as delaying the gas return for increased extraction capability on short barrels due to gas impulse delay.  The Young mfg LBC carrier is chromed and the best quality chromed carrier I have ever seen, and has special design features such as fluting and increased bearing surface.  It also has smaller cutout on the rear and extended firing pin ramp.  It's also the heaviest semi carrier I know of (same as an M16 carrier).  Of those three I would get the RRA if on a limited budget, or the LBC if I had lots of money.  I haven't seen the semi-LMT carrier yet, but for full auto I would get the LMT if I had the cash.  I have an semi-LMT coming to try out though.  For semi use, I think the LBC is the heaviest, definitely heavier than the RRA, and probably heavier than the LMT.

I plan on using LMT groups in my two favorite ARs, but they are expensive and I can't afford to get one for each of the other rifles.  I was hoping for another alternative. Not that I actually need new bolts or carriers, mind you.  I don't even need them for my two favs, as I haven't experienced any trouble with them.  I guess it is more about having absolutely peace of mind in the best quality parts for the two babies.  Come to think of it, why the hell am I trying to find ways of spending more money?  I guess I want a better than average bolt in each of my precious ARs becaue I feel each and every one is a better than average rifle.

You too, huh?

Yeah AK Mike is right on.

I have'nt noticed any different functional difference compared to that of a standard AR carrier, Except it is a little harder to clean due to the extended firing pin "hood" area.

Would an LBC carrier go good in a workhorse gun?
IE not a rangebaby?

I am building my first top o the line SHTF rifle, and would like the best setup I can get my grubby hands on.

Would the heavy mass of the LBC delay the unlocking of the bolt? What is the advantage of this? Less stress on locking lugs? More accuracy? Longer bolt and carrier life?

Thanks AK_Mike (or whoever) for whatever knowledge you may offer!

Well, the LBC would give you a reliability edge.  The heavier carrier helps in stripping the next round from the mag and locking the bolt into batter.  A little carrier won't have as much inertia to ensure complete cycling as much as the LBC.  We are talking a really small degree of edge here though.  I don't think the weight of the carrier delays unlocking, it's more of a matter of chamber pressure and return gas.  The PRI Fat Boy gas tube and the key of the LMT carrier both have features that delay the return gas giving it a fraction more dwell time while the chamber pressure drops.  That makes for less force needed to extract the fired case, less chance to rip the head of the rim off leaving you with a broken case in the chamber, and less stress on the locking lugs.  Normally these are non-issues, and are only significant in short barrels less than 16".  IMO I would just go with the LBC carrier.  Easier to clean, less wear on the receiver, increased weight for reliability.  Unless your barrel is shorter than 16", there is not much need to address trying to delay the return gas impulse.  I would, however, use an HD spring such as the Wolff HD spring in the extractor unless you use the LMT bolt.  The LMT bolt is the most advanced and superior no matter what carrier is being used.  It has a different extractor system already.  Denny's Guns will plans to offer one of the ultimate combo's - the LBC Semi Carrier with an LMT bolt.  I don't think you can get much better in a semi-auto setup.