This is probably about the 20th time I've written such an article, but it is important. Basic understanding of elemental components aren't inherent, and there are always "new" folks out there needing to know. So this time I want to talk about the most important component to accuracy in any AR-15. That there would be the barrel.
I freely admit to being a barrel snob. I'm a competitive shooter and I want all the points I hold for. The only way to ensure peak accuracy is to install a truly good "match-grade" barrel.
Now, you can't swing a dead cat without hitting somebody's "match-grade" barrel out there in our industry. Folks, no objective standards apply. None. "Matchgrade" is a term entirely freely applied. To me, a true match-grade barrel will win championships. There are more, but here are three names to know: Krieger, Lilja, Schneider. Satern fits in there too.
The best way to judge the quality of a barrel is by cost. Sorry. But it's true. A handmade or custom-made barrel is expensive. It costs a lot to produce because of the quality controls. It takes time.
There are tiers of "good" barrels. Those from the first tier, represented by the makers I named. The next tier are "graded" barrels: these are produced relatively en-masse and then checked over for things like straightness and end-to-end uniformity. Shilen, Douglas, and Pac-Nor offer such options. The other tier are barrels that are maybe good, maybe not. They can all claim to be "match" barrels. This last follows the PDL grading method: Pure Dumb Luck gets you a tube that hammers. Some of my Colt HBAR barrels shot as well as all, and others didn't.
I no longer tell everyone they need to have a truly good barrel. Truly good barrels are ballpark $500, ready to shoot (turned to contour, extension fitted, chambered, port drilled, assembled onto the upper). A little less maybe, but not much. What do you get with a truly good barrel? I've had enough experience with this to tell you such a barrel, correctly chambered and installed underneath a likewise correctly done free-floating fore-end tube, will easily group under 1 MOA, often well under. Not can, will. If your AR-15--no matter the barrel dimensions or length--won't shoot under an inch at 100 yards, then there's your solution. And now consider your judgment: what level of accuracy do you expect? If you can be happy with groups between 1 and maybe 1-1/2 MOA, then something from the "second tier" will be rewarding....