Build Your Base: The Aero Precision M4E1 Lower Receiver

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Last Updated on January 12, 2021.

When it comes to receivers and receiver sets, Aero Precision really knows their stuff. I don’t know of any manufacturer that makes better receivers for a better price. That’s why I use a lot of Aero Precision receivers. And the Aero Precision M4E1 Lower Receiver is hands down one of the best lower receivers you can get.

This lower receiver is awesome at every stage. It makes for a great building experience. And it delivers an outstanding shooting experience.

Even though I love this lower receiver, I will admit that it may not be perfect for every rifle. But the limitations of this lower receiver have nothing to do with operation, durability, or any other super important factor.

Want to know what’s so special about this lower receiver? I’ll tell you.


Aero Precision M4E1 Lower Receiver Review: (Almost) The Best Lower Receiver Possible

From a very high level, the M4E1 lower hits all the bases: price, ergonomics, function, durability, and all the rest.

But there’s nuance to all these characteristics. And, unfortunately, there’s a reason or two not to use the M4E1 lower receiver. I’ll get to those.

Finish

I’m kind of a stickler for finishes on my receivers. And I know that not everyone is a stickler for clean anodized finishes. But the M4E1 lower has the best finish you can get for the price.

Yes, there are companies that produce smoother, glossier anodized finishes. But none of them sell lower receivers at a better price.

For the money, the M4E1 has the best finish you can get.

It’s a nice deep black, rather than the grayed out black that you see on many budget lowers. And the finish is nice and smooth. Again, this is in contrast to many budget lower receivers, where the anodized finish has a matte finish.

Overall, the M4E1 has a super attractive finish.

The finish is also super durable. We use several M4E1 receiver sets on rental guns at the range. They get banged up a lot. And the finish resists wear and dings impressively well. It’s not invincible. But it’s quite durable.

So, even if you put a lot of wear and tear on your guns, the finish will hold up. And your gun will look cool and stay safe from corrosion for as long as possible.

All in all, two thumbs up on the finish.

Design

This is not a standard AR-15 lower receiver. And this is where the limitations of this lower receiver emerge.

But, limitations aside, the design offers several benefits.

First, the angular design improves impact resistance, according to Aero Precision. I’ve seen M4E1 receivers get beat up a lot. And they do indeed seem very impact resistant.

However, I can’t verify if the M4E1 lower is actually more impact resistant than a standard AR-15 lower receiver. But the M4E1 is very durable, regardless of whether or not it’s significantly tougher than a standard lower.

Here’s what I find to be the best part of this lower receiver, though: the threaded bolt catch roll pin.

Installing the bolt catch roll pin is pretty much my least favorite part of assembling a lower receiver. And it’s the part where most people tend to scratch the finish on their lower receiver.

Nice, angular design.

The threaded bolt catch pin removes this hassle altogether. You just install the pin with a hex driver. It takes like two minutes. And I’ve never scarred the finish on the lower receiver while installing the bolt catch on an M4E1 lower.

This is honestly the best part of this lower receiver.

You may be concerned about the threaded pin coming loose. However, the threads are tapered to keep the pin from backing out. And, you can put a tiny dab of threadlocker on the threads, if you’re really worried about it.

But—be warned—if you use threadlocker, you probably won’t be able to get the threaded roll pin out without heating your lower receiver up to loosen the threadlocker. And, if you strip out the threaded pin, you’re going to have a bad time.

I’ve never seen an issue with the threaded bolt catch pin backing out, with or without threadlocker, though. So the ease of installing and replacing the bolt catch is more than worth the almost non-existent risk of backing out, to me.

Additionally, the M4E1 lower has an integrated trigger guard that’s very nice. And it’s skeletonized to keep the weight about the same as a mil-spec trigger guard.

Obviously, it saves you the trouble of installing a trigger guard. But it’s flared slightly to give you easy access to your trigger, with or without gloves.

However, all the corners are rounded to eliminate any harsh edges that might chew up your knuckles. The trigger guard is very well designed in terms of both performance and ergonomics.

Integrated and skeletonized! Win-win!

Look at that! No harsh edges

So, what’s the downside to the enhanced design?

Two words: parts compatibility.

Most standard AR-15 parts fit the M4E1 lower receiver just fine. Any standard lower parts kit will work.

But, if you want enhanced controls, you’re more limited in which ones you can use. Not all enhanced bolt catches fit the M4E1. Ambidextrous bolt catches sometimes have fit issues, too. And there are some enhanced magazine releases that don’t fit right.

However, not all enhanced controls have fit issues on the M4E1. If you want to use some enhanced lower parts, they’ll probably work. It’s just wise to check the fit before you go all in.

Also, I’ve heard that there are some upper receivers that the M4E1 doesn’t fit. But I’ve never actually encountered one. So I’m not exactly sure which upper receivers don’t fit. Rumor is that they’re out there, though.

On the other hand, the safe/fire markings on this lower receiver match up with both 45 and 90-degree throw safety selectors.

But, minor parts compatibility issues aside, I find the design of the M4E1 lower receiver to be more than worth the slightly limited options for enhanced controls.

Performance

As you might have guessed from looking at the Aero Precision M4E1, there’s nothing super special about it in terms of performance. There are no serrations on the front of the magazine well or crazy magazine well flare.

However, the magazine well has a more aggressive flare than a standard AR-15 lower receiver. That gives you a slight edge when it comes to getting the magazine into the well, which means faster reloads and easier loading.

The magazine well is slightly more flared than a mil-spec lower.

The more aggressive flare inside the magazine well translates to a slightly more aggressive flare on the outside of the magazine well, too. This might come in handy if you put your support hand on the front of the magazine well. That’s not my grip technique. But it’s there if you need it.

Obviously, the performance isn’t a massive improvement over a standard AR-15 lower receiver. But the operation is a little bit faster and easier. And even a little bit counts

Thoughts on the Lower Half

In the end, the M4E1 could be the only lower receiver you ever use. It’s that good.

No, it’s not perfect for every application. If using certain enhanced controls is a deal breaker for you, and those parts don’t fit the M4E1, you’ll obviously need something else.

However, the M4E1 can do anything you need if you can be just a bit flexible in terms of which lower parts you use.

And one last thing: the price. The Aero Precision M4E1 Lower Receiver is less expensive than many standard AR-15 lower receivers. Really, the price is the only thing about this lower receiver that’s pretty much the same as a standard AR-15 lower.

So you don’t have to compromise your budget to get the benefits of this lower receiver. That’s why I can recommend it for any rifle.

Feel free to use this lower receiver for everything, because it’s good enough to do anything you’d need an AR-15 to do.