1012,
Rob has a sticky at the top of the General Discussion forum that contains a chart that compares the major AR brands, you may want to check it out if you haven’t already. You can read it here.
You want to look for properly staked gas keys as this adds to reliability, good expamples of this can be seen various places around the board. Colt, FN, LMT, and Bravo Co (maybe others too), typically have the proper gas key staking, others like Bushmaster, RRA, Armalite, etc may need to additional staking.
You want proper staking on the receiver extension if you are going with a collapsible stock, most here also prefer a Mil-Spec extension for their collapsible stock as it is said these are stronger with better thread engagement. Most of the aftermarket collapsibles require a Mil-Spec extension. The brands listed above tend to apply in this area too.
For your bolt, you would want an MPI tested and shot peened bolt with the proper extractor insert and possibly an o-ring, for best dependability. I just replace my factory RRA BCG with a Bravo Co FA BCG for the above reasons. The Bravo Co and LMT are everything a BCG should be and less expensive than I could find a new Colt one for.
For the barrel, chrome lining may help increase barrel life and make cleaning easier, but may not be as accurate as a SS barrel. There are several different twist rates to choose from. The M4 normally is 1x7 which will stabilize the longer, heavier bullets. Mine is a 1x9 RRA factory barrel, which stabilizes most bullets, it does better with lighter bullets than a 1x7 but not as well with heavier bullets. There are other twists available too like 1x8 and 1x12. There is a military standard for the barrel steel too, but are several good choices too. A 5.56 chamber may be more reliable for you than a .223. The top tier manufactures tend to have 5.56 chambers, while many of the others tend to have .223, althought they may be marked differently. There is also the Wylde chamber, but I don’t know much about it personally.
Many prefer M4 feed ramps on their upper receiver. These ramps are extended further than rifle ramps into the receiver for better feed reliability. Some people may argue their need. The use of a reciever with M4 ramps mandates the use of a barrel extension cut for M4 ramps too, but the reverse is not necessarily true. However, I would say if you want them, make sure both upper and barrel extension have them. My RRA does not have M4 feed ramps and runs fine. Some manufacturers do these ramps differently from others. I’ve heard that RRA dremels theirs after the upper is assembled. I spoke with them and they confirmed this, althought I never really got an answer as to why, just that that is how they do it. Some people feel that the exposed unanodized aluminum is bad. Mine is not cut like this so I can’t say one way or the other.
There are probably other things I am forgetting, but it pretty much boils down to this. I feel you can group AR’s into two groups Mil-Spec and Commercial. While commercial is not necessarily bad, you asked about the most reliable. The most reliable, or at least those with the features that most contribute to reliability, are what I’d call Mil-Spec (although I’m sure someone would argue with me about that too). And those that are closest tend to be LMT, Colt, Bravo Co, many custom builds, etc. Those that I would consider in the commercial group (those with commercial receiver extensions, non MPI bolts, maybe non “F” FSB, non chrome lined barrels, no M4 feed ramps, etc) are often Bushy, Armalite, RRA, Olympic, etc, however many of these may be offered in part or whole on certain models.
There are other things like buffer weight, springs, etc that can effect reliability. But as many have already suggested to you for the best bang for the buck out of the box you can’t go wrong with an LMT.
But piece together whatever you like, just make sure you know what to look for. My commercial RRA has run fine for me since day one. I assembled the lower and had ADCO build me the upper. I have since started replacing some of the parts we mentioned for better piece of mind and long term dependability. However, I never had a problem with it even before I started swapping, but then I don’t run my rifle REAL hard.
Good Luck!
-RD62
P.S. Almost forgot one of the things that may effect reliabilty most is the magazines you use. I just got some MagPul P-Mags, and so far they have been great! Light, inexpensive, good feeding, everything I could want. Their are inexpensive mags and then there are cheap mags. P-MAgs are inexpensive. Friends don’t let friends buy cheap mags!
