Zach P. enjoys shooting his AR-15 and regularly gets together with buddies to go shooting.
One of the friends has a large piece of property where they can go shooting anytime they want.
On a particular day, it was a little bit rainy, but the group didn’t let it stop them from shooting their AR-15s.
You see, one of the guys drives a big van with double doors on the back, so they decided to shoot from inside the van with the back doors open.
Things were going great until Zach had an issue with his rifle.
Unbeknownst to Zack, when he pulled the trigger on his AR-15, it ended up with a squib round.
A squib round is a malfunction where a bullet doesn’t have enough force to exit the barrel, so it becomes stuck.
This can be a dangerous – potentially deadly – malfunction if the shooter doesn’t notice that the projectile is stuck in the barrel.
This type of malfunction usually results in a catastrophic failure of the weapon if another round is fired into the one lodged in the barrel.
In Zack’s case, he pulled the trigger after the squib round, causing an explosion of his rifle.
He said he didn’t notice the squib round because he was in a timed race with his buddies.
But Zach was lucky…
The explosion blew out at the weakest point, which was the magazine in this case.
Neither the stock nor the barrel exploded, which could have seriously injured Zach.
The rifle was severely damaged including the extractor, receiver, and bolt catch.
Thankfully, Zach wasn’t injured
Now, as you know, the AR-15 is one of the most popular rifles in the U.S.
It’s versatile, reliable, and a highly customizable and modular weapon.
Which is why it’s one of the most popular weapon platforms to build at home.
The large amount of customization means that gun owners can swap out the trigger, barrel, and build a rifle that fits their exact needs.
Yet, anytime you have a gun with so many available aftermarket parts for customization it can create challenges.
One issue with mixing and matching of different parts is called receiver slop.
Receiver slop occurs when there is play or wobble between the upper and lower receiver of the rifle.
The manufacturing tolerances could both be at the low end of the range, which means there is a much larger gap than if the parts were custom fit at the factory.
In most cases, receiver slop doesn’t compromise the safety of the rifle.
But it can lead to performance issues when accuracy is the top priority.
So, here are a few things to understand to avoid receiver slop.
Why does it happen?:
Receiver slop is the tiny amount of movement you can get between the upper and lower halves of an AR‑15.
The two halves of the rifle are held together by the front pivot pin and the rear takedown pin that locks the halves into one unit.
The goal is for the two halves to fit perfectly together with no movement, but a bit of wiggle is common, and many shooters never even notice it.
Manufacturing tolerances are the cause of the wiggle.
That’s because AR-15 receivers are built to slightly different tolerances from each manufacturer.
So, if you have two receivers from different manufacturers the tolerances could be slightly different.
Sure, two receivers from the same brand can have different tolerances, but it’s usually more noticeable when mixing brands.
The good news is, receiver slop isn’t a “defect” in the rifle, and it should still function as designed.
How it affects performance:
The upper receiver has the most effect on accuracy, because it holds the barrel, bolt carrier group, and gas system.
Conversely, the lower receiver contains the trigger group, magazine well, and buffer.
Since there is a split in what the upper and lower receiver do, receiver slop doesn’t typically hurt reliability.
The truth is, a majority of reliability issues come from magazines, bad ammo, or the gas system.
But receiver slop can still affect accuracy.
You see, at long distances, you need a steady rifle.
But with even a slight movement between the upper and lower it affects your sight picture.
So, precision shooting at long range can make receiver slop more noticeable.
Fixing receiver slop:
The best way to avoid receiver slop is with prevention when you start building or buying a rifle.
If you are building a rifle, purchase both the upper and lower receiver from the same manufacturer.
Companies that make both design them to work closely and hold their tolerancing tight enough to mitigate slop.
You can even purchase matched sets that have been dimensionally matched before leaving the factory.
Now, if you already have a rifle with noticeable slop there are a few things you can do.
One option is something called an Accu-Wedge.
This is a small flexible piece of polymer that fits into the rear of the lower receiver.
It fills the small gap that causes slop and reduces wobble.
Another option is using tensioning screws.
Some lower receivers have built-in screws that make it easy to adjust.
By tightening the screws, it presses the upper receiver into the lower receiver, eliminating the space and potential wobble.
If the lower receiver doesn’t have the built-in screws, there are aftermarket kits you can install.
