How to Purchase, Upgrade, or Build an AR15

The best piece of advice we can give anyone looking to purchase and AR-15 sporting rifle is to build your own, using the parts and upgrades you want. A budget AR 15 like this Bushmaster can often be found during sales for about $500 and uses all mil-spec components. And while Mil-spec AR-15s are accurate, reliable, and fun to shoot, you'll inevitably find yourself wanting to make improvements.

After the first time you shoot your budget AR15 rifle, you'll notice that the mil-spec buttstock is clunky and uncomfortable, so you'll upgrade it with a Magpul MOE Buttstock for about $40. But while you're at it, you might as well upgrade the pistol grip and forend with a Magpul MOE Furniure Set that runs around $100. At this point, your rifle is much more comfortable to shoot so you'll start accessorizing it and that typically starts with some aftermarket sights like these Magpul MBUS Gen 2 Sights for $100. You may also decide to upgrade the little things like an ambidextrous safety selctor, a larger mag release button, and an enhanced bolt catch because they are cheap and desireable upgrades, so that's another $80. Finally, you realize that you are now $800 in to your AR15 (after shipping costs and tax) and realize it is a shame to still be running that mil-spec trigger. You want something better than a Nickel Teflon mil-spec trigger but don't want to spend a fortune on a competition trigger so you find one you like at around $100 like this very popular Rise Armament Drop-In Trigger.

At this point you hopefully see the big picture, a mil-spec rifle is a great start, but spending a bit more for a rifle with some popular upgrades may actually save you money in the long run, or better yet, start with a stripped lower receiver and complete it it with the exact parts you want.

Important AR15 Building Laws

check local laws / Ca compliance pistol / rifle

AR15 Pistol vs Rifle

check local laws / Ca compliance pistol / rifle

Carbine vs Mid Length vs Rifle Gas Systems

The gas system of an AR15 is what cycles the rifle and loads the next round. This process is accomplished by releasing a portion of the backpressure created when a bullet is fired through a gas tube that exits at the bolt carrier group, causing it to cylce backwards against the buffer tube spring that then pushes back on the bolt carrier group, chambering the next round. There are three standard palcements of the gas port (vent) on an AR15 refered to as carbine length, mid-length, and rifle length.

  • A carbine length gas system has the gas port at 7.5"
  • A mid-length gas system has the gas port at 9.5"
  • A rifle length gas system has the gas port at 12.5"

The placement of the gas port along the length of the barrel determines how much backpressue is released to the bolt carrier group. The further down the barrel the vent hole is placed, the less pressure is released into the gas tube and less force is applied to cycle the bolt. Or, to be a bit more acurate, the closer the gas port is to the end of the barrel (known at the dwell length) the less pressure is released.

For an AR15 rifle to cycle correctly, repeatedly, and reliably, the pressure released must be within a desired range. Too little pressure and the bolt won't be able to chamber the next round and too much pressure, called over-gassing, will make the rife cycle harder and run dirtier as it is sending excess gas to bolt carrier where it is vented.

  • A carbine length gas system is recomended for 14-16" barrels
  • A mid-length gas system is recommended for 16-18" barrels
  • A rifle length gas system is recommended for 18-22" barrels

In addition to the placement of the gas port and the overall barrel length, the cycling of an AR15 is also affected by the buffer tube spring, buffer weight, bolt carrier weight, and in some cases an adjustable gas block.

Choosing a Trigger

Single Stage - Trigger does not move before the trigger breaks, ideal for combat, home defense, and competition shooting. Could be dangerous with a light trigger. Two Stage - trigger with intentional slack (typically desired for precision shooting to reduce break force) safer when used with a light trigger Flat blades allow you to choose your own leverage depending on how far down teh blade you pull. A curved trigger (or one with a saddle) tends to settle your finger in the same place for consistant leverage. Break - The point at which teh trigger mechanism releases. A crisp break is typically preferred as the trigger stays in place until the break pressue is released and the trigger releases. A soft trigger, or a rolling trigger, will continue to move until the break pressue is reached. Overtravel - rearward travel on the trigger after the trigger breaks. More overtravel means the trigger has to move back further to rest and the additionl movement is more likely to move teh rifle. Minimal or no overtravel is desired. Reset - after the rifle has fired, the trigger must be released so that it can move forward and re-engage for the next shot. Shoe - A separaet piece of material on the blade used to adjust the finger purchase on the trigger. Slack - movement before resistance is felt, Smooth - constant building pressure, Gritty - rough, not smooth. Stacking - rough "steps" in the pull that can cause a false break Alighter hammer releases faster.

Tuning an AR15

Lighter BCG, less recoil, requires less gas. Lighter BCG tend to wear faster (?). Most AR15s are overgassed and have overweight buffers. Adjustable gas block can use a lighter buffer and bcg. goal is less recoil. A standard bcg and buffer w/ overgassing is ultimately most reliable. Heavier buffer has slower cycle, for more dwell time and more reliable extraction. Heavier bolt has more weight to help load the next round especially in a dirty ar15. comp rifle, clean, light, low recoil (less muzzle rise), faster cycling. for a duty or home defense gun, upgrade to a heavier buffer.


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