Longer Gas Tube
The AR-15 runs on a gas system, which is what drives the explosion needed to push the Bolt Carrier Group backward. Higher gas pressure on the BCG is a given when the gas block in the barrel is placed close to the gas chamber. That means a pistol-length tube would give you tremendous recoil, affecting the accuracy achievable in follow-up shots. Longer tubes of rifle length can deliver a much smoother and more accurate shooting experience. This is the reason why so many precision rifles carry upgrades with regard to tube length.
Optimal Twist Rate
Twist rate is described as the ratio between the number of rotations of a bullet, to the distance in inches that it has to travel to make them. For instance, a 1:8 twist rate signifies exactly one rotation taking place inside every 8 inches that the bullet travels down the barrel. Heavier bullets need more spin, for higher accuracy, which means a smaller ratio works best. For light bullets, you need less spin to prevent over-stabilization, which means a higher ratio is better. When picking out ammo, you need to match it with the twist rate of your AR15’s barrel to make sure the two work well together.
Your gun stock of choice depends mostly on personal preference, as it well should. You need good balance between a stabilizing solid check weld, comfort level among other factors. The options available range among collapsible, fixed-length, and PDW-style varieties. You need to pick what suits your type of gun use. Precision shooting would call for adjustments accounting for use of more powerful optics, at which point you will want to check out the options you have under adjustable precision stock.
Muzzle Device to Mitigate Recoil
A bullet exiting a barrel leaves an expanding trail of gas, which pushes the rifle backward, a movement that the shooter experiences as felt recoil. Budget AR-15s typically ship with a muzzle device that combats muzzle flash during low-light engagements, but not the impact recoil. The muzzle brake upgrade can pick up that slack, helping maintain a steady sight on the target. It basically redirects the expanding gases and faces them in the opposite direction, reducing recoil dramatically, and consequently improving your shooting experience. Most importantly, though, follow-up shots become much easier to get back to.