AR question for a newbie

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When people talk about building a AR gun with uppers and lowers? Do all brands mix and match? Because people say oh I have this upper and this kind of lower?
Thanks
 
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AR style guns are like legos, IF you are using quality parts, interchangeability should not be an issue.

You can use any "brand" of upper or lower and it will "mix and match".

Some older preban lowers had some "out of spec" issues. "Out of spec" problems can also show up today, but you will rarely find that. The last case of a new lower being out of spec was CMMG selling bad lowers to a distributor who knowingly sold them as "blemished" instead of "POS out of spec".

Tolerance stacking on the manufactured specifications can and does occur, but it's not something to worry about.
 

F2386

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Not only can you mix and match lowers and uppers, but you can also mix and match every single part. For example, DPMS lower parts kit in a Spikes Tactical lower with a DSA buffer assembly. This lower can be mated with a Colt upper receiver that sports a Daniel Defense barrel and a Bushmaster BCG. Just buy from reputable names and you'll be just fine.
 
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mind you, since you didn't specify, this does not hold true for AR's chambered in 7.62 Nato. Only the ar-15 platform.
 
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The only real exception is with some of the older Colt stuff because they used larger cross pins to attach the upper and lower together. You can buy adapters to use them with standard mil spec parts, but they aren't a straight up fit. As long as you stick with good current manufacture mil spec parts they all play together nicely. For example, I have a Spikes lower with some PSA lower parts, Geiselle trigger group, and a complete BCM upper.
 

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yup. I have a YHM lower from the NES Group buy. DPMS LPK (minus trigger). Geissele trigger. "no name" A2 buttstock, and Rock River complete upper topped with a Nikon scope. Works together like a charm!
 
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Only things that really don't mix and match are older colts have larger front takedown pin which they have adapters for, mil spec and commercial parts, barrel mounted sights are for the most part for a specific diameter barrel so make sure what you have matches up.
 
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yeah they all mix and match except for the ones that don't [smile]

seriously though the AR has to be the most prolific firearm in production by multiple manufacturers and it's a small miracle that they work as well as they do together.

The notable exception would be Colt, particularly the pre-ban civilian series:

Colt LARGE PIN LOWER won't work with most uppers unless you use an adapater, which get mixed reviews
Colt BLOCKED LOWERS won't work with bolts that don't the half-moon cutout
Colt can also have different sized fire control group pins, which if you buy a lower built, that shouldn't really be a problem

Also, some makers will vary their finish color to some degree. Like the older Colts and Bushmasters are more of a grey oppose to the darker matte black you see today.

Lastly, you may need to change out your buffer weight (in the lower) depending on your upper configuration, but that's a relatively cheap and easy switch.
 
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This is the first I heard of this. Please explain more.

Bought the 1st one and I went to build everything was tight, too tight. The rear pivot pin would not go through and the alignment between the upper and lower were about 1/8" off. Drove back to Ludlow, John took the parts off the lower and put it on another lower while I waited. Took it home and set it aside for a week while I waited for a rear BUIS. After BUIS install I decided to oil the heck out of it because I wouldn't be shooting it for a while. Tried to push the rear pivot pin out with my finger, no go, had to use a punch to drive it out. once out I noticed that again the alignment was off again by about 1/8" and would only line up if I forced the heck out of it. Thinking it was my upper I went to 4S and bought a Stag lower. Moved the LPK over to the Stag and it fit like a glove, nothing was too tight.
I then trouble shot the old lower and found out that the forward assist housing was hitting the shoulder by the buffer. One hour with the Dremmel and I finally got it to the point of not having to force the pivot pin.
Not a good experience on the first build.
 
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Bought the 1st one and I went to build everything was tight, too tight. The rear pivot pin would not go through and the alignment between the upper and lower were about 1/8" off. Drove back to Ludlow, John took the parts off the lower and put it on another lower while I waited. Took it home and set it aside for a week while I waited for a rear BUIS. After BUIS install I decided to oil the heck out of it because I wouldn't be shooting it for a while. Tried to push the rear pivot pin out with my finger, no go, had to use a punch to drive it out. once out I noticed that again the alignment was off again by about 1/8" and would only line up if I forced the heck out of it. Thinking it was my upper I went to 4S and bought a Stag lower. Moved the LPK over to the Stag and it fit like a glove, nothing was too tight.
I then trouble shot the old lower and found out that the forward assist housing was hitting the shoulder by the buffer. One hour with the Dremmel and I finally got it to the point of not having to force the pivot pin.
Not a good experience on the first build.

Wow, thanks for adding the details to this. I have been to John's shop and looked at his stuff, but don't own any myself. I have also read of many builds on here, and there were even "NES" lowers, but I never read of this issue before. My thought initially was that maybe your upper was the culprit until you mentioned that it worked perfectly on the Stag. Maybe John will see this and chime in with some thoughts on what could have happened. Maybe there was an out of spec batch, or something, and you just got "lucky".
 
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Colt lowers with a sear block installed will work fine with an AR-15 carrier. The only carrier that will not work is the M-16 style.

Maybe but wtf is a "AR-15 carrier" [grin]

Problem is there is the Mil Spec for the M16 then everybody with a bridgeport makes up the AR-15 standard as they see fit. So yeah, the Mil Spec bolt carrier won't work with the COLT sear block but everything else I would rate at "probably".
 
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Remsport Mfg

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We had a problem with 25 units it was a machine program problem. I have pulled those units and the last run is OK without problem.
The too tight 25 units have been scrapped and the new units are available. Hco. 2/2 cav I will replace the lower you have with one of the new ones if you want.
John
 
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Maybe but wtf is a "AR-15 carrier" [grin]

Problem is there is the Mil Spec for the M16 then everybody with a bridgeport makes up the AR-15 standard as they see fit. So yeah, the Mil Spec bolt carrier won't work with the COLT sear block but everything else I would rate at "probably".

"BCG - bolt "carrier" group, I believe that was what he was referencing by saying AR-15 carrier.

In addition to that, most BCGs sold today are the m-16 style, at least every one that I have compared over the past year, or 2 has been the FA style.
 
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mind you, since you didn't specify, this does not hold true for AR's chambered in 7.62 Nato. Only the ar-15 platform.

It is too bad the AR-10 platform is not the same. I have been wanting to get into this area, but picking a manufacturer seems to be a much more important process as opposed to the AR-15 platform.
 
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"BCG - bolt "carrier" group, I believe that was what he was referencing by saying AR-15 carrier.

In addition to that, most BCGs sold today are the m-16 style, at least every one that I have compared over the past year, or 2 has been the FA style.

yup, I am familiar with the BCG, we're old friends in fact

anywho, my point is there is a Mil Spec M16 BCG and then there is everything else (non-mil spec). There's no one design spec for a AR15 BCG.
 
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Doesn't the OP also have to worry about commercial or MILSPEC buffer tubes?

No, that only comes into play when he is deciding on a butt stock. If he goes with a rifle style (A1, A2, new MOE, etc.) then there is only one type of buffer tube. For carbine style adjustable butt stocks there is the 2 kinds but you just buy based on the stock you want to use. I would always recommend going mil-spec for the buffer tube if possible since there are more choices for stocks available. Honestly the best move here is to buy a package like those offered by PSA, where they have the lpk, buffer tube and spring, and buttstock of your choice all in one kit.
 
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what Terminator said, and every AR build thread should have the disclaimer:

Building your own AR with quality new parts does not typically save you any money. People do it more for the experience.

and for most people, there's no need to mix and match new upper and lower brands. you will see mismatached upper and lower has a used preban receiver in a ban state. And I suppose there's some folks that have some techy reason to mix and match but I've never had such a need.
 
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what Terminator said, and every AR build thread should have the disclaimer:

Building your own AR with quality new parts does not typically save you any money. People do it more for the experience.

Building your own will save you the 11% Federal tax that is charged on Long Guns (as long as you don't order the parts all at once).
 

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Building your own will save you the 11% Federal tax that is charged on Long Guns (as long as you don't order the parts all at once).

You can avoid the tax if you order the lower first then the upper second. Or vice versa. The proper tools required to build just a single AR will cost you more than if you bought a completed upper and a completed lower and slapped them together. On the other hand, if you find that you've got black rifle fever then the tools will pay themselves off in no time.
 
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