Before laying down your money for an AR-15, go through this pre-purchase checklist
Buying a new or used AR-15 requires a plan and some pre-purchase inspection to make sure the juice is worth the squeeze. Few things are sadder than falling out of love with a rifle because a blemish or quality control issue pops up post-purchase. There’s no way to look at a rifle and know how it will perform, but there are indicators of attentive manufacture that signal quality craftsmanship. Here’s a handful of things to check to help ensure a lifetime of bliss with the new purchase.
Nuts and Keys
Any AR-15 made to meet military specifications has to have a staked castle nut around the lower receiver extension (buffer tube) and a staked gas key on top of the bolt carrier group. Most AR-15s will never be shot enough for either of these requirements to have any effect, but a rifle with these details done correctly indicates the manufacturer is trying to maintain a high standard.
The castle nut holds the buffer tube in place. If the nut comes loose, the buffer tube and stock will spin freely and this makes shooting difficult. If the castle nut isn’t staked, it’s easy enough to do at home with the right tools. However, something that only takes a moment and wasn’t done correctly doesn’t bode well for quality control on all the things you can’t see in the gun shop.
The gas key has two small bolts holding it in place on top of the bolt carrier group. If those two bolts don’t remain tight forever, the gas key will come loose and allow gas to escape prior to cycling the bolt. This is a guaranteed malfunction that is easily prevented.
This little detail has slipped past many an AR-buyer. The rifling inside the barrel has to be in a tight enough twist rate to stabilize the bullets fired through it. The most common twist rates are one full rifling twist in nine inches of barrel (1:9) or a full twist in seven inches of barrel (1:7). The 1:9 has been around for a long time and stabilizes most ammunition found in any gun store. The 1:7 twist does better with the heaviest 5.56mm bullets that usually hover around 77 grains in weight.
If the price was right, I wouldn’t worry too much about the barrel’s twist rate. There’s anecdotal evidence to suggest that expanding bullets fired through slower twist barrels have better terminal effects. There’s pretty conclusive evidence that 77-grain bullets need a 1:7 twist for optimal accuracy. However, the twist rate only becomes an issue if the consumer has a specific purpose for the pending purchase. AR-15’s that will be used for long-range precision work should have the 1:7 twist.
The Gas Tube
The interface between the gas tube and the bolt carrier’s gas key is easy to get wrong and has a noticeable impact on accuracy. Fortunately, it’s an easy thing to check. Remove the upper receiver group from the lower receiver and place it upside down on the gun counter. Next, remove the charging handle and bolt and replace the bolt carrier back in the upper receiver. Slide the bolt carrier back and forth in the upper receiver and watch for movement of the gas tube when the bolt carrier moves into the closed position. If there is any gas tube movement, the key is impacting the gas tube when the action cycles and the rifle will struggle to shoot sub-minute of angle. The bolt carrier moves at high velocity and any contact with the gas tube sends the impact right to the gas block near the muzzle. It’s like tapping the barrel with a hammer during the shot.
These are a handful of inspection points that can uncover issues before purchasing the rifle. While there are no guarantees that a rifle will shoot well, this short checklist will eliminate some of the more egregious manufacturing errors.