Building an AR, does choice of receivers matter much?

[Tango24]

I have been doing a lot of reading (especially on this site!) trying to work out what will go into my upcoming AR-15 build. I find a lot of material regarding barrel choices and triggers, no problem there. And things like hand guards, muzzle devices, sights, etc. seem to rely mostly on the builder's personal preferences.

But when I read about receivers it seems there aren't a lot of strong reasons for choosing one over the other. This is really apparent when people post their build sheet's here and more often than not the lower and upper are even different brands.

So... does my choice of upper and lower really make much difference? Is there any thing to gain by buying both from the same brand?

Thanks in advance!

 

[USACS]

If you buy both from the same brand and from the same company, you can have them ensure that both mate up correctly with no play. That being said, upper and lower receivers from quality companies tend to have very little to no play anyways.
One of the big reasons why you should buy from a reputable brand is because of tolerances. Quality companies have exacting standards and very high QC.

 

[jasonfaz]

I would say the biggest difference in receivers that you'll see is in the lower. If a true full ambi lower is something that's valuable there are only a few to choose from (KAC, AXTS, San Tan, LWRC, etc). But even if the lower you pick isn't ambi out of the box, there are a shit ton of options out there that will allow you to make a non or semi ambi lower full ambi.

With the upper you have monolithic offerings from Mega, LMT, VLTOR that might pique your interest and a few side chargers - JP PSC, American Spirit, 2 Vets Arms, etc - that are available should that style of upper fit your application better than a standard rear charging upper. The only other difference with uppers that I've run across - and it's minor - are bolt release cut outs. I like a wider contact surface and use a lot of Seekins bolt catches. They don't fit well with Vltor, JP and some of the uppers that aren't cut wide enough to accommodate that kind of enlarged catch. Occasionally they'll still function and just scratch the hell out of the upper, and other times they'll cause various failures. Hopefully that helps...

 

[BigBlue&Goldie]

In my opinion the receivers are one of the least important parts of an AR15 as long as they are in spec. If you need ambidextrous controls or a special feature not included on a standard forged receiver, then they become more important. With that said, I have had a lot of uppers that have been out of spec, and potentially only 1 lower that might be out of spec (haven't had the time to measure it out).

I like assembling on lowers from local manufacturers because I think it's kind of neat, but I really think you are better off spending your money on your barrel, trigger, optics/mount, and even your bolt carrier assembly. Hell, I think its more important to have a ridgid handguard setup than a fancy receiver set.

 

[Drifter™]

From an accuracy standpoint, it's important that the face of the upper receiver is square.

Squaring The AR Receiver Face - Shotgun News

 

[JB02]

It comes down to preference. Since I scored a complete Seekins upper (receiver and hand guard), I wanted a matching lower. The choice then came down to billet vs forged. For forged, it really made no difference at all. My my mil discount, the Seekins forged lower was comparably priced. But the billet models offered options like ambi safety, hex key instead of roll pins for the bolt catch, integral trigger guard, etc. All of that said, had I found a screaming deal on an already assembled LMT lower (or something similar) with the trigger I wanted, I would have gone that route.

If you get a MK12 build from High Caliber Sales, the upper and lower receivers are almost guaranteed not to match, but they shoot just fine.

The point of all of this is that when choosing your receiver set, think about the options you want with it. Some hand guards only work with some upper receivers because of proprietary components (e.g., Seekins). AR-15.com has an AR builder that does an OK job of walking through the parts and compatibility of all the components (keep in mind, it has a somewhat limited range of options).

If you're fine with plane jane, just get a forged and a standard LPK. Make sure the components not to skimp on are the barrel, free floating hand guard, and a good trigger.

 

[KULT]

This and how tight the barrel extension bore is will have a good bit to do with how accurate it is . Some companies are getting hip to this and making it a point to be more precise.. Also using a good barrel extension is important, but you might not have too much choice in that when buying off the shelf.

BCM Upper Receiver Assembly - M4 Flat Top

"(Inside Diameter for barrel extension slightly undersized for a tighter fit to the barrel and a more accurate rifle.)"

Genesis 308 Upper Receiver | Genesis CNC

In designing the Genesis 308 Upper Receiver, great care has been taken to ensure a high degree of precision. With special attention taken in the barrel extension area. The precision machining in the face of the barrel extension seat and bore diameter will allow you to build a more precise rifle.

From an accuracy standpoint, it's important that the face of the upper receiver is square.

Squaring The AR Receiver Face - Shotgun News

 

[oneshot onekill]

I work for an AR Manufacturer. My job is Tech Support and Customer Service so I see it ALL! When receivers are too tight I get a call. When receivers are too loose I get a call. When the color doesn't match I get a call. Etc... Etc... Etc.
ALL AR manufacturers that "make" Forged Receivers (upper or lower) make them from Forgings that come from the same few companies. The difference is in how the raw Forgings are machined. "Milspec" has tolerances, and those tolerances mean that even an Upper and Lower from the same AR Manufacturer can be loose, or tight, or not line up exactly right. (The comment in the above post about the inside diameter for the Barrel Extension being "slightly undersized" makes me cringe because that's just stupid! I'll bet over half of those come back because a builder couldn't get the barrel extension to fit even after beating it with a 2x4!)
Anyway, I digress... But I just had to mention that. Here's the bottom line. If you're going to use a forged Upper and Lower get them from a reputable company that has a Logo and color anodizing you like and GREAT CUSTOMER SERVICE! Because if you have a problem like them being too loose or too tight or anything else, you want to be able to simply contact the company and get the problem taken care of as quickly and painlessly as possible.
If you want a "Billet" set that's a whole different Ball Game! Most of what I mentioned above about fit and finish is the same but there are a Shit-ton of different styles and shapes and weights. Some Billet receivers are great and some are just heavy and unnecessary. You can end up with something really cool or some Robo-turd looking monstrosity.

...That's my 2cents. FWIW.

 

[GH41]

I would get both from the same manufacturer to avoid tolerance stacking. Look at Aero Precision. Good quality at fair prices.

 

[346ci]

All of my personal rifles are built using Mega receivers. When building rigs for customers, I reccommend the same.

If for some strange reason I can't get Mega, Vltor.

 

[oneshot onekill]

I would get both from the same manufacturer to avoid tolerance stacking. Look at Aero Precision. Good quality at fair prices.

So... Define "Tolerance Stacking"... And how does buying both parts from the same manufacturer avoid it? If Milspec has tolerances, then anyone is susceptible to Tolerance Stacking. Right? I don't disagree with buying both from the same manufacturer. But tolerance stacking is going to happen. It's just easier to deal with one company from the standpoint that they will be more likely to help you if their upper doesn't fit their lower. FWIW...

 

[Ballista One]

From an accuracy standpoint, it's important that the face of the upper receiver is square.

There is not soul in existence who could prove on a bet that "squaring" the receiver face has any effect on accuracy. The receiver is either made right or it isn't. There are several other parts/factors to consider in making the rifle more accurate, fixing one has no affect on overall accuracy.

 

[KULT]

This has proven just ask any engineer who works on designing AR-15 uppers. While it is not the end all be all of things that need to be checked but it is important. As for the receiver being made right, guns are generally serviceable through a wide range of spec and wear. One forged receiver set might produce a gun that is 1.25 MOA shooter and another might produce one that is 1 MOA shooter solely based on tolerances .If your barrel extension doesn't have a good seating surface against the receiver accuracy will suffer at longer ranges where microscopic movements will change your POI.
Same goes for how tight it fits in the extension bore... Companies like GAP use billet sets to keep the tolerances tighter

Squaring the receiver face on an AR for long range work is just one part of the accurizing process. No different than truing an action or tightening the lock up on a bolt gun. Bedding actions or swapping receivers on M1a for a three lug unit to create more surface area for the bedding.

There is not soul in existence who could prove on a bet that "squaring" the receiver face has any effect on accuracy. The receiver is either made right or it isn't. There are several other parts/factors to consider in making the rifle more accurate, fixing one has no affect on overall accuracy.

 

[BigBlue&Goldie]

I don't disagree that squaring the face is important to extreme accuracy, but I don't think these lapping tools are precise enough to make a difference. In other words, unless the shank of the lapping tool has an extremely tight fit to the bore of the receiver, you are just further stacking tolerances. There is a reason why Remy 700's aren't squared by hand tools. To do it right, you would have to have a precise fitting mandrel to indicate the upper in a lathe or mill and square it that way.

What good is squaring up the face of the receiver if you don't also square up the barrel extension, barrel nut, bolt contact surfaces, and bolt face? You can spend all kinds of time splitting hairs, but at the end of the day, 99.9% of shooters can't shoot a gas gun well enough to reach it's potential.

 

[Drifter™]

There is not soul in existence who could prove on a bet that "squaring" the receiver face has any effect on accuracy. The receiver is either made right or it isn't. There are several other parts/factors to consider in making the rifle more accurate, fixing one has no affect on overall accuracy.

I'm not sure if you're saying that it doesn't matter, or that it can't be corrected.

I've moved a proven barrel from one receiver to another, only to see accuracy degrade slightly. Removed the barrel, squared the receiver face, reassembled, and accuracy returned to previous performance. The difference wasn't much, but enough that I could notice. I suppose that the primary factor is how the bolt face matches up to the barrel in the extension.

While I don't think squaring the receiver face will have a noticeable effect in every case, it's an easy precaution to take. Just as I wouldn't want an out-of-square receiver face, I also wouldn't want an imperfect barrel crown, ammo with excessive runout, etc. There are many pieces to the puzzle. Perhaps taking reasonable precautions will more likely result in an accurate rifle.

Here's an informative link from a reputable source: What Makes an AR Accurate ? Whitley Offers Answers « Daily Bulletin

 

[GH41]

"I don't disagree that squaring the face is important to extreme accuracy, but I don't think these lapping tools are precise enough to make a difference"

Believe this man!

 

[Ballista One]

I'm not sure if you're saying that it doesn't matter, or that it can't be corrected.

I'm saying that this single operation doesn't make a difference. Clear? Among the many worthless purpose built AR-15 tools on the market, that "lapping" tool is king of the hill. It was design to separate the unwashed masses from their money and to instill a false belief that anyone with a drill motor and a cheap ass wood vise can true and upper receiver. If you don't have the tools and gauges to take accurate measurements of the receiver before and after performing the lapping operation, you have no idea what was done and what wasn't done to the receiver. Likely, you did little more than remove maybe a half mil of anodizing. The OD/ID dimensional fit of the barrel extension and upper receiver is far more important than the squareness of the face but there is NOTHING your average joe with a Brownell's account can do about it if either or both are out of spec.

 

[Drifter™]

Likely, you did little more than remove maybe a half mil of anodizing.

I agree, but it was only on a portion of the receiver face.

This isn't my pic, but helps to illustrate the point:

So with a half millimeter removed from one side of the receiver face, how much does that move the muzzle of a 20" barrel? How does it affect the relationship of the bolt in the extension, and the load sharing of the lugs?

If a half millimeter is inconsequential, how much before it matters? Is it the same for all receivers, or will it vary based on other factors?

Not a pissing match, but serious questions...

 

[richidaho]

My last three builds were GT lowers. GTVC - AR 15 They have a Teflon screw in the lower that allows tightening of the upper to the lower. I have used Lilja barrels and DPMS mil-spec flat top uppers. I have had sub MOA accuracy with factory ammo in all three builds and have been very happy with them. The company also offers engraving and consecutive serial numbers. There worth checking out.

Rich L

 

[Ballista One]

Half a mil is five ten thousandths (0.0005) of an inch, not half a millimeter, and it's inconsequential. You're way more likely to have fitment issues with the barrel nut or the threads on the receiver. Again, neither of these can be repaired in your garage. Like I said before, the receiver is either made correctly or it isn't. If you can document a measurable increase in accuracy across two concurrent builds by only squaring the receiver face, you'd be the first one to do it. Along with Brownell's and its DIY tool selection, ALL of the gun rags that publish woodshed gunsmiffing articles on accuracy enhancements have incentive to do so and it has nothing to do with accuracy.

I have dialed in and fly cut the receiver face on at least 20 upper receivers over the years in a valiant effort to validate this squaring argument and I can't document a measurable improvement. All of the before and after shot groups are a statistical push. I challenge you to find a single riflesmith who will true an AR-15 upper receiver and extend a money back guarantee as to an increase in accuracy.

 

[BigBlue&Goldie]

I agree, but it was only on a portion of the receiver face.

This isn't my pic, but helps to illustrate the point:

So with a half millimeter removed from one side of the receiver face, how much does that move the muzzle of a 20" barrel? How does it affect the relationship of the bolt in the extension, and the load sharing of the lugs?

If a half millimeter is inconsequential, how much before it matters? Is it the same for all receivers, or will it vary based on other factors?

Not a pissing match, but serious questions...

It could've been a high spot, or it could've been off axis pressure being applied to the lapping tool. If you put that upper in a vice and hung a hand drill from the lapping tool, it would inevitably put more pressure on the lower part of the receiver face. I would rather spend $20 and send the stripped upper to D-Tech and have him indicate in a lathe.

 

[Birddog6424]

I work in a gun shop where we have 20 different lowers to sell at any given moment. All the Idaho companies, PWS, Ambush Tactical, Seekins, Founding Fathers, 2A Armament, and of course, everyone else from Noveske to Mega, Spikes, Aero, to you name it. My honest opinion which I am asked for and give often, is it doesn't really matter.

As suggested above, find the features you want, or even the lower that is cosmetically appealing, and run with it. Out of the legions of rifles we have built, I can count on one hand how many times there was an issue. Nearly all of them were in fit issues to the upper, and all of them were easily correctable.

In my humble opinion, from what I have seen, the Balios Lite from 2A Armament is the most innovative upper and lower I have seen in a while. Extremely well designed, and can easily shave 4 to 6 ounces off the upper and lower of other manufacturers while maintaining structural integrity. 2A has been around for years making parts for lots of other manufacturers, they finally took their experience and started making their own.

 

[jasonfaz]

While the receiver set will never be as high on your build's priority list as the barrel, trigger and optic I wouldn't overlook some of the things that can make a pretty noticeable difference depending on your specific set up.

For example, (note that I'm personally a fan of ambi lowers for ergo reasons) I just bought a San Tan lower to replace a Noveske Gen II lower I have on my Grendel. There are specific reasons I did so and at a cost of only $50 or so over what a Noveske Gen II lower would run and could argue it's actually much cheaper than buying a non-ambi and then dropping $$ on a Norgon, and all of the std operating control parts to complete the lower. The San Tan has a rear tensioning screw machined into the lower that allows you to tighten up the lower/upper fit. It has an over travel adjustment screw machined in to the lower as well that has been very helpful in fine-tuning my Geissele NM trigger. It has flush cup sling attachment points machined in as well. Noveske Gen IIs happen to include none of those things. Now, some people can give two shits about any of that - which is fine - but I'd really think about what it is you foresee this rifle being and look into the granular details that will make it just that based on your specific application and preferences. I can't tell you how many people I see buy run of the mill parts yet expect their rig to be as versatile, accurate, and pleasant to shoot as the guys that add putting in the time to plan out every detail and pay $30 more dollars.

Price the whole thing out and weigh the costs vs what you're willing to pay for....and think "I'd rather have it and not need it than need it and not have it". It'll save you dolla's in the long run my man!!

 

[Tango24]

Lot's of great info and discussion, thanks everyone!

The purpose of this build will be informal paper punching at a range with 100 and 200 yds positions. So I won't need range finding capabilities just a system capable of small groups. I am new to precision AR shooting and this will be my first build. My experience is with Rem 700's with which I became accustomed to groups 1/4 - 1/2 MOA (usually 0.2" - 0.3"). I was surprised to learn that people are getting groups like that with the AR platform and now I want to try my hand at that too.

I decided to shop for the barrel first and I eventually ordered a stainless White Oak Armament 18", 1-7 twist. I'm sure that'll be a good start. I've used Shilen barrels in bolt actions and believe the WOA will be a good performer here. By the way, the folks at WOA were very helpful in assisting me with this selection.

My next priority is actually the trigger, but I need receivers to start attaching these things to, hence this thread. Before this thread I wasn't aware of the side charging uppers. What are the advantages to those? They don't seem to be real plentiful, certainly not as much as standard uppers. Why do people use them? Are these geared toward competitors? Since my shooting will be informal, personal enjoyment maybe I wouldn't realize the benefit of them.

Thanks again for all the help, much appreciated!!

 

[bustin]

There is not soul in existence who could prove on a bet that "squaring" the receiver face has any effect on accuracy. The receiver is either made right or it isn't. There are several other parts/factors to consider in making the rifle more accurate, fixing one has no affect on overall accuracy.

Yeah and most are not square regardless of the name on them.
If the barrel extension is not square to the bore of the receiver are your bolt lugs touching evenly on all sides? That is really the only question anyone needs to ask.
I've been an AR smith since the early 90s and very very few receivers are square because of the way they are setup in the jigs. All it takes is checking with a Brownells tool, I use a lathe but the tool is much cheaper. How many people do you hear say "my rear sight is dialed all the way to the left"...guess why. Builders can slap stuff together and hope everything works ok or they can take every precaution to ensure they work correctly... Yugo VS Mercedes.
OP, do yourself a favor and buy a Mega forged receiver. The bore is a little tighter and will hold the barrel extension square to the bore by fitting snug to the diameter of the extension, you don't need to true the receiver it if that is the case.

 

[jasonfaz]

Before this thread I wasn't aware of the side charging uppers. What are the advantages to those? They don't seem to be real plentiful, certainly not as much as standard uppers. Why do people use them? Are these geared toward competitors? Since my shooting will be informal, personal enjoyment maybe I wouldn't realize the benefit of them.

Thanks again for all the help, much appreciated!!

There are various reasons why they are considered beneficial. Some prefer the charging mechanism located further up the rifle to aid in maintaining cheek weld if one must charge the weapon during a course of fire. Some people shoot subsonic ammunition at times - essentially turning your AR into a quasi bolt gun -requiring you to charge the rifle after each round fired. The side charging set up once again helps the shooter maintain cheek weld. Some consider the protruding handle reciprocating with the carrier to be a downside of the side charger. In that type of design you'd also use the side charge handle as a forward assist. Outside of rifles like the SCAR, ACR, etc., I am aware of only one "traditional" AR design with a side charge mechanism that does NOT reciprocate with the BCG. That would be the JP PSC set up which also requires the use of their carrier in order to function as designed. It also is the only side charger I am aware of with a separate, right side forward assist and has the ability to charge from either side or traditional rear charging handle. Boils down to personal preference...

 

[Ballista One]

@ Tango24 - The JP PSC is little more than a boutique upper and its market share in the US is effectively zero. JP does a fair amount of export business and as such this upper was designed for countries such as the UK where semi-auto rifles are prohibited. I'd argue you will be much better off with a traditional AR-15 upper receiver as you will not be hamstrung by proprietary parts and prices.

 

[jasonfaz]

@ Tango24 - The JP PSC is little more than a boutique upper and its market share in the US is effectively zero. JP does a fair amount of export business and as such this upper was designed for countries such as the UK where semi-auto rifles are prohibited. I'd argue you will be much better off with a traditional AR-15 upper receiver as you will not be hamstrung by proprietary parts and prices.

While I'd certainly agree that JPs PSC uppers are less common and more expensive than run of the mill, I'm not sure how one could come to the conclusion that they have no market share in the US. Any insight to share around the source of that info? Just curious.

It also seems odd to suggest JP - or any manufacturer - would design an upper intended to be used on a semi-auto rifle platform for countries not allowing ownership of said rifles. Not sure I follow what you're saying there? I'm 100% sure JP had no such intentions when designing the PSC line of receivers. My comments above with respect to a possible benefit of any side charging system aiding in the charging of the weapon while using ammunition not capable of cycling it wasn't intended to suggest that the design intent of those uppers had anything to do with that specific use case. It's merely something I use mine for when I'm teaching the kids or eradicating bunnies in the back yard.

 

[Ballista One]

While I'd certainly agree that JPs PSC uppers are less common and more expensive than run of the mill, I'm not sure how one could come to the conclusion that they have no market share in the US. Any insight to share around the source of that info? Just curious.

It also seems odd to suggest JP - or any manufacturer - would design an upper intended to be used on a semi-auto rifle platform for countries not allowing ownership of said rifles. Not sure I follow what you're saying there? I'm 100% sure JP had no such intentions when designing the PSC line of receivers. My comments above with respect to a possible benefit of any side charging system aiding in the charging of the weapon while using ammunition not capable of cycling it wasn't intended to suggest that the design intent of those uppers had anything to do with that specific use case. It's merely something I use mine for when I'm teaching the kids or eradicating bunnies in the back yard.

Well, if your a 100% sure, I must be 0% right. That being said, SEMI-AUTOMATIC rifles are prohibited in the UK. You can own an AR-15 that isn't SEMI-AUTOMATIC. Noodle that for awhile...

Sent from my XT1056 using Tapatalk

 

[cal50]

The only issues I have seen in AR receivers has been upper and lower fit , buffer tube concentricity / perpendicularity with the receiver and the buffer retainer pin location. The buffer tube is a coarse fit thread and the buffer tube really needs to be line up reasonably close for non-binding bolt carrier operation. I fixed a friend build on a receiver he purchased during the panic buying and his buffer retainer pin was way off proper location.

Buy a good quality receiver and build away , just look for the common problems and build accordingly.

 

[jasonfaz]

Well, if your a 100% sure, I must be 0% right. That being said, SEMI-AUTOMATIC rifles are prohibited in the UK. You can own an AR-15 that isn't SEMI-AUTOMATIC. Noodle that for awhile...

Sent from my XT1056 using Tapatalk

How is that even relevant to the topic of discussion or your previous post? You deliberately made a comment directed at the OP stating that the design of side charging uppers - specifically JPs PSC - were designed for localities restricting the sale of semi autos.....which, again, is false. It had nothing to do with legal ownership of SA rifles nor did it relate in any way to rifles (like the Bradleys) that omit the gas system completely yet ascetically resemble an AR15 in std config.

There ain't nothin to noodle my man. Do us a favor and try to refrain from derailing threads with pointless, completely inaccurate information.

 

[clmayfield]

I don't disagree that squaring the face is important to extreme accuracy, but I don't think these lapping tools are precise enough to make a difference. In other words, unless the shank of the lapping tool has an extremely tight fit to the bore of the receiver, you are just further stacking tolerances. There is a reason why Remy 700's aren't squared by hand tools. To do it right, you would have to have a precise fitting mandrel to indicate the upper in a lathe or mill and square it that way.

What good is squaring up the face of the receiver if you don't also square up the barrel extension, barrel nut, bolt contact surfaces, and bolt face? You can spend all kinds of time splitting hairs, but at the end of the day, 99.9% of shooters can't shoot a gas gun well enough to reach it's potential.

I think the lapping tool is good for uppers that are way off. Will it be as good as a properly set up lathe? No. But there are some uppers out there that have some pretty big high spots on the face to the point that they run out of adjustment on their iron sights trying to sight it in. For those guys, it is hard to say that this tool won't get things better, if not perfect.

Is it the best method for this job? No, but a lot of AR-15 enthusiasts assemble these things in the garage and don't have access to a lathe or a mill. For those guys, this tool gets them a little better off. A good idea that I heard was to use this tool as an indicator for squareness. Put some transferable color, like a crayon on the lapping face of the tool, put it in the receiver, and see if you can color the entire receiver face. If so, your receiver is probably "good enough."

As to accuracy, it seems like it would have to improve things. You free float the handguard trying to relieve stress from the barrel. Squeezing that nut down on a receiver face that is not square seems like it would add some stress. Especially if it is way off. That is more a comment for Ballista One. For folks shooting off hand with a red dot sight, I agree, the difference in accuracy would probably not be noticeable. We happen to be on a precision shooting forum where some people are expecting near bolt action performance from their AR's. That means they have to worry about getting a whole bunch of things right on this platform.

 

[nedceifus]

USACS said it.

 

[NewsShooter]

I bought my complete lower from Seekins, when everything was in short supply and prices were skyrocketing Seekins kept their prices the same, which will keep me coming back to them and the quality products they produce. When you figure in the cost of their complete lower vs a bare lower, and buying a parts kit, buffer, rear stock, it's a decent deal especially when you look at the trigger that's comes in the Seekins.