I remember the first time I slapped together a lower receiver. Everything looked pretty straightforward, but there was this nagging question in the back of my head: are the aluminum pillars supposed to touch the action screws? It felt weird, like something was off, but I chalked it up to being new to it. Turns out, that little detail can make a surprisingly big difference in how your rifle performs, and frankly, how much of a headache you’ll have down the line.
This isn’t some high-brow technical debate; it’s about practical application and avoiding unnecessary problems. We’re talking about parts that might seem insignificant, but they play a role in the whole damn picture.
Why Those Little Pillars Matter So Much
Let’s get down to brass tacks. You’ve got your aluminum lower receiver, and sticking out from the inside, usually near the rear takedown pin area, are these little nubs or pillars. Their job, in a nutshell, is to support the rear of the bolt carrier group (BCG) when it cycles. Think of them as tiny, albeit important, shock absorbers and alignment guides. When the BCG slams rearward, these pillars are there to take some of the impact and make sure it doesn’t just bounce around like a loose pinball.
The real question, the one that gets guys scratching their heads, is whether these pillars are supposed to be in constant contact with the action screws. For the uninitiated, action screws are the little screws that often hold the trigger guard in place, or in some designs, might be part of the pivot pin assembly. The common wisdom, and often the correct engineering, dictates that these pillars should not be jamming up against those screws. Why?
Because when they do touch, it usually means something is out of alignment, or you’ve got a receiver that’s not quite up to snuff dimensionally. This can lead to a gritty action, increased wear, and even malfunctions.
It’s like trying to slide a drawer that’s rubbing against a screw – it just doesn’t move smoothly, and eventually, something’s going to get damaged.
I’ve seen some budget builds where these pillars were almost welded to the action screws straight out of the box. The user probably didn’t even notice, or they figured it was just how it was. Fast forward a few hundred rounds, and they’re complaining about stiff operation and needing to constantly clean it. More often than not, it’s these little things, these seemingly minor interferences, that cause the most persistent headaches. It’s not rocket science, but it does require a bit of attention to detail. If your pillars are making contact, it’s a blinking red light saying, ‘Hey, something’s not quite right here, and you should probably investigate before it becomes a bigger problem.’
The primary function of these pillars is to provide a consistent surface for the bolt carrier group’s rear to rest against, preventing excessive movement and vibration. They’re designed to have a tiny bit of clearance, just enough to allow for smooth operation without letting the BCG rattle around like a maraca. When aluminum pillars touch action screws, it signifies an interference that can impede this smooth operation.
It suggests a potential issue with the receiver’s machining, the dimensions of the trigger guard, or even the alignment of the pins. This isn’t just about aesthetics; it’s about the mechanical integrity and reliability of your firearm.
The goal is a smooth, consistent cycling action, and any unnecessary friction or binding between parts is counterproductive to that goal.
What to Look for: The Devil’s in the Details
So, how do you actually check if your aluminum pillars are getting too friendly with the action screws? It’s not complicated, but it requires a good light source and a bit of poking around. With the upper receiver removed and the bolt carrier group out, take a flashlight and shine it into the lower receiver. You’re looking at the area around the rear takedown pin. You’ll see those small aluminum pillars, and then you’ll see the action screws, usually threaded into the trigger guard assembly. Carefully examine the contact points.
You’re looking for any shiny or scuffed marks on either the pillars or the action screws. These marks are tell-tale signs of contact. If you see them, even faint ones, that’s your indicator. Another way to check is by gently inserting the bolt catch.
Sometimes, an interference with the pillars can make the bolt catch feel stiff or not seat properly. You can also try to wiggle the trigger guard assembly slightly. (See Also: Are The Aluminum Pillars Supposed To Touch The Action Screws )
If it feels overly tight or binds up in a way that seems connected to the pillars, that’s another flag. The ideal scenario is to have a small, consistent gap between the pillars and the screws. This gap allows for the natural movement and vibration of the BCG without creating undue stress or friction.
This isn’t something you’ll necessarily feel while just holding the rifle. You have to actively look for it.
I’ve spent more than a few evenings with a flashlight and a magnified glass doing this check, especially on builds where I wasn’t 100% sure about the tolerances of the parts I was using. It’s a simple diagnostic step that can save you a lot of grief later on. For example, I once built a rifle using a less-common lower receiver and trigger guard combination.
Everything seemed to function, but the BCG was just a bit rough cycling. A quick inspection revealed slight scuff marks on the rear pillars, precisely where the action screws were positioned.
It wasn’t a catastrophic failure, but it was definitely an interference that was causing unnecessary wear and that less-than-smooth feel. A bit of careful filing on the action screws solved it, but I wouldn’t have known to look if I hadn’t gone searching for that tiny detail.
Here’s a quick rundown of what to observe:
| Observation | Meaning | Verdict |
|---|---|---|
| No marks on pillars or screws, slight visible gap. | Ideal clearance. Parts are not interfering. | Good to Go |
| Faint scuff marks or shiny spots on pillars/screws. | Minor contact occurring. May cause slight resistance. | Investigate |
| Deep gouges or significant wear on pillars/screws. | Significant interference. Likely causing functional issues. | Immediate Action Required |
| Trigger guard feels extremely tight or binds when installing. | Potential interference between guard and receiver, possibly involving pillars. | Investigate |
This table gives you a clear visual guide to what you should be looking for. It’s about understanding the subtle cues your firearm is giving you. Don’t ignore them.
Common Mistakes and Why They Happen
One of the most common reasons for aluminum pillars touching action screws is simply using parts that aren’t perfectly compatible or within tight enough tolerances. Not all AR-pattern lowers and trigger guards are created equal, even if they’re supposed to adhere to the same basic specs. I’ve learned the hard way that sometimes, even reputable brands can have slight variations in their machining. This can lead to interference issues like the one we’re discussing.
Another mistake is not checking during the build process. Many people assemble their rifle, and if it functions, they stop there. They don’t go back and do these detailed inspections. They might experience slightly rougher cycling or increased wear over time, but they attribute it to other factors or just accept it as normal for that particular build. This is where that ‘good enough’ mentality can bite you. It’s like building a piece of furniture and not tightening every screw because it looks okay – it’ll wobble and fall apart sooner.
Then there’s the issue of aftermarket parts. While many aftermarket trigger guards are excellent, some are designed with slightly different dimensions to accommodate specific features or aesthetics. This can inadvertently cause their action screws to protrude further or sit at an angle that brings them into contact with the lower receiver’s pillars. I once tried a fancy, skeletonized trigger guard that looked awesome, but the screws were just a hair too long. It wasn’t obvious until I did a thorough inspection, and then it was clear why the action felt a bit gritty. It took me about three tries to get the screw length right by carefully sanding them down.
Over-tightening the action screws can also sometimes contribute to this problem. While you want the trigger guard snug, cranking down too hard can slightly deform the aluminum around the screw hole, pushing the screw into the pillar. It’s a subtle effect, but it can happen.
The advice I usually give is to tighten them until they’re snug and then just a quarter-turn more. Anything beyond that is usually unnecessary and can cause more problems than it solves. It’s easy to get carried away with the idea of making things ‘secure,’ but in precision machining, over-enthusiasm can be your enemy. This is why I generally recommend sticking to matched sets of lower receivers and trigger guards from the same manufacturer if you’re building from scratch and want to minimize these potential headaches. (See Also: Are Black Screws Rust Resistant )
It’s not always the cheapest route, but it often saves you time and frustration in the long run.
Real-World Use: Does It Actually Cause Problems?
Okay, so we know if the aluminum pillars are touching the action screws, but does it actually matter in the real world? My honest answer? Yes, it can, and often does. It’s not always a show-stopper that will make your rifle explode, but it’s a constant, low-level impedance that degrades performance and longevity. Imagine running a race car with a tiny pebble stuck in the brake caliper. It’s not going to stop the car immediately, but it’s going to cause drag, wear, and make the brakes less effective over time.
In a firearm, this interference can manifest in several ways. You might notice a slightly rougher cycling of the bolt carrier group. Instead of a smooth, fluid motion, it might feel a bit ‘gritty’ or ‘sticky’ as it moves rearward and forward. This can be particularly noticeable during rapid fire. It can also lead to increased wear on both the pillars and the action screws, and potentially on the BCG itself, as metal is constantly rubbing against metal where it shouldn’t be.
More seriously, in some cases, this interference can contribute to reliability issues. While it might not be the sole cause of a failure to feed or eject, it can be a contributing factor, especially when combined with other variables like ammunition type, dirt, or improper lubrication. A system that’s already under slight stress from internal friction is less forgiving of external variables. I’ve seen forums where people are troubleshooting jams, and buried deep in the comments, someone mentions a slight interference with their rear pillars, which, once resolved, seemed to improve reliability. It’s not always the primary culprit, but it’s often an overlooked detail that can be part of a larger puzzle.
I remember a friend who was having intermittent ejection issues with a rifle he built. He’d tried everything – different magazines, different ammo, adjusted his gas system.
Nothing seemed to consistently fix it. When I finally got my hands on it, I did a quick check of the lower receiver, and sure enough, the rear pillars had visible scuff marks from the action screws. We addressed that interference, and while it didn’t magically solve every single hiccup, his rifle started cycling noticeably smoother, and those ejection problems became far less frequent.
It was a good lesson in how small, seemingly insignificant details can have a cumulative effect on overall performance and reliability. It’s the kind of thing you’d never guess is the problem unless you’re specifically looking for it.
How to Fix It: Practical Solutions
Alright, you’ve found that your aluminum pillars are indeed touching your action screws. Don’t panic; it’s usually a fixable problem. The goal is to create that small, consistent gap we talked about. The most common and effective method is to carefully file down either the action screws or, less commonly, the pillars themselves. I generally prefer to work on the action screws because they are typically made of a harder material and are easier to control the amount you’re removing.
You’ll need a fine-grit file – a small needle file or a diamond file works best. Start by removing the trigger guard assembly.
Then, apply a very small amount of material removal from the tip of the action screw that is making contact. Work slowly and deliberately. After a few light passes with the file, reassemble the trigger guard and check for clearance.
You can do this by eye, by feeling for binding, or by using a thin piece of paper to see if it slides between the pillar and the screw. The key is to remove just enough material to eliminate the contact, not to overdo it.
It’s much easier to take more off than to put it back on. (See Also: Are Blue Concrete Screws Waterproof )
If you’re working with a lower receiver where the pillars themselves are the issue (this is rarer, but possible with poorly machined parts), you might need to very carefully file the tops of the pillars. Use the same fine-grit file and be extremely cautious. You want to maintain their general shape and not remove too much material, as they are important for supporting the BCG. A slight chamfer or bevel on the edge of the pillar can also sometimes help if the screw is just barely catching an edge.
Here’s a step-by-step approach:
- Remove the upper receiver and bolt carrier group.
- Carefully remove the trigger guard assembly.
- Examine the action screws and pillars for signs of contact (shiny spots, scuffs).
- Select the screw or pillar that is making contact.
- Using a fine-grit file, carefully remove a small amount of material from the offending part. Work in light, controlled strokes.
- Reassemble the trigger guard and check for clearance.
- Repeat steps 5 and 6 until sufficient clearance is achieved (a small, consistent gap).
- Clean up any metal shavings and reassemble the rifle.
I’ve also heard of people using very thin shims between the trigger guard and the lower receiver to adjust its position, but I find direct material removal to be more precise and less prone to creating new alignment issues. If you’re not comfortable with filing metal, it’s always best to seek help from someone experienced or a gunsmith. However, for most DIYers, this is a manageable task.
One time, I had a particularly stubborn set of action screws that were just a hair too long. I ended up using a small bench grinder with a fine grinding wheel to quickly take off the excess, followed by filing and polishing to get a smooth finish. It saved me a lot of time, but it’s a method that requires a steady hand and careful control.
For most people, a file is the safer bet.
People Also Ask: Your Questions Answered
What Supports the Rear of the Bolt Carrier Group?
The rear of the bolt carrier group (BCG) is primarily supported by the rear takedown pin area of the lower receiver. Specifically, small aluminum pillars or bosses that extend from the inside of the lower receiver provide a contact surface. These pillars absorb some of the rearward impact and help guide the BCG’s movement during the cycling process, preventing excessive jarring and potential damage.
Can a Bolt Catch Rub on the Bolt Carrier Group?
Yes, a bolt catch can sometimes rub on the bolt carrier group, but it’s generally not by design and can indicate an issue. The bolt catch is designed to engage the rear of the BCG to hold the bolt open. However, if the bolt catch is bent, installed incorrectly, or if there are dimensional issues with either the BCG or the lower receiver, it can cause unwanted contact or friction between the two components during normal operation.
What Are the Pillars in an Ar-15 Lower Receiver for?
The pillars in an AR-15 lower receiver, often referred to as bosses or support lugs, are small protrusions located inside the receiver, typically near the rear takedown pin. Their main purpose is to provide a stable and consistent support surface for the rear of the bolt carrier group (BCG) as it cycles. They help to absorb the shock of the BCG’s rearward travel and maintain alignment, contributing to smoother operation and reducing stress on the receiver.
Can Action Screws Hit the Bolt Catch?
Action screws, which typically secure the trigger guard assembly, can potentially interfere with the bolt catch mechanism. If the action screws are too long, improperly seated, or if the trigger guard is misaligned, they can protrude into the path of the bolt catch lever or its associated spring and detent. This interference can prevent the bolt catch from functioning correctly, making it difficult to engage or causing it to disengage prematurely.
The Aluminum Pillars Touching Action Screws Verdict
Look, nobody likes spending extra time fixing something that should have been right out of the box. But when it comes to firearms, attention to detail isn’t just about bragging rights; it’s about reliability and longevity. So, when you’re building or maintaining your rifle, and you’re wondering, are the aluminum pillars supposed to touch the action screws? The short answer is no, they absolutely should not. That contact is a sign of interference that can, and often will, cause problems down the line, from a gritty action to potential reliability issues.
It’s a simple visual inspection that can save you a lot of headaches. If you find contact, don’t ignore it. Take the time to address it, whether it’s a few careful passes with a file on the action screws or a minor adjustment elsewhere. It’s a small step that can make a big difference in how your rifle performs. Trust me, I’ve learned from experience that overlooking these little things is a good way to end up frustrated and potentially dealing with more significant issues later on.
Final Verdict
So, to wrap it up, if you’re building a rifle or doing some maintenance, take a few minutes to check if your aluminum pillars are kissing those action screws. It’s a common oversight, but it’s one that can directly impact how your rifle cycles and how long it lasts.
Remember, a smooth action is a happy action. If you find contact, the fix is usually straightforward – a little careful filing can go a long way. Don’t be afraid to get your hands dirty and inspect those parts. It’s better to spend an extra fifteen minutes now than to spend hours troubleshooting a problem later that could have been prevented.
Take a good look, and if you see any signs of interference, know that it’s a fixable issue. It’s part of the learning curve for anyone who enjoys working on their own gear, and ultimately, it leads to a more reliable firearm. What’s the worst that can happen? You learn something new and end up with a better-functioning rifle.
