Never had an issue putting pistol tubes on 'mil-spec' uppers. I usually install the tubes on the lowers.

 

Yeah, I never built an AR before and it's not like I can just order a whole bunch of parts to see what works and what doesn't, at least not until I'm back to working again.

 

the upper does not take the tube, Lower does. Order a Pistol tube and install it on the lower and the brace should fit. Lower must be sold to you as a Pistol. BTW Braces are not designed to fit Carbine tubes as it would be to easy to create a potential illegal Short Barreled Rifle.


Finestkind

 

Lower must be sold to you as a Pistol.

As I understand it;
All AR lowers are sold as pistols.
They can be made into rifles but once that is done they cannot be converted to a pistol.

Federal law requires that you be 21 years or age or older to purchase a stripped receiver or frame. If a frame or receiver can only be made into a long gun (rifle or shotgun), it is still a frame or receiver not a handgun or long gun. However, they still are "firearms" by definition, and subject to the same GCA limitations as any other firearms. See Section 921(a)(3)(b). 18 U.S.C. Section 922(b)(1) makes it unlawful for a licensee to sell any firearm other than a shotgun or rifle to any person under the age of 21.

https://www.americanrifleman.org/articles/2016/7/14/building-ar-15-pistols-at-home/

• A factory fresh AR lower receiver that has never been part of a firearm can be used to build a pistol, carbine or rifle. If a lower receiver is built into and registered as a pistol first, it can be stripped down and converted into a rifle in the future. If the receiver built into a carbine or rifle first, it must always remain part of a rifle and cannot ever be used to build a pistol.
• It's not necessary to use a lower receiver stamped "Pistol" or one that is marked with the specific caliber of ammunition you plan to use when building an AR pistol. The markings are irrelevant just as long as the lower is brand new from the factory at the start of the build. Many companies are marking their lowers "Multi-Cal" these days in order to avoid confusion.

 

Will an AR pistol brace designed for a pistol buffer tube fit a carbine tube?
No

 

I was asking because I didn't know if the overall dimensions were different, or just the length. I should have clarified.

 

Sorry, I shouldn't have mentioned "rifle tube" as I didn't realize those are also round (just did some googling). I meant pistol vs carbine. The carbine tube has extra material on the bottom - it's not round like a pistol tube. You'd be trying to put a square peg in a round hole if you try to use a pistol brace with a carbine tube.

 

buffer tube: mil-spec vs commercial - tube diameter, threads are the same
length: rifle vs carbine vs pistol - rifle is a fixed stock BUT a pistol brace on it will work if the tube diameter is correct or can be shimmed. Carbine tubes have the bottom ridge with adjustment holes, the number of which can vary per mfg. Note the is such a thing as a 'blind' buffer tube (extension) for AKs etc with an adapter. Pistol tubes are carbine tubes without the bottom ridge and detent holes. Check out the Brownell site and AR builder sites for more info.
Be wary of cheap or no name buffer tubes, the INSIDE diameter can be out of spec.

 

THanks bud!

 

very confusing question and details. Terrible OP. Mechanical or legal question depends on the barrel length. Can vs should. Duct and JB weld can do almost anything.

A short pistol buffer (non-adjustable) with a brace with a short (<16") barrel upper = pistol

A short barrel on a long (carbine, adjustable) buffer and attached pistol brace "may" be considered a sbr, IF SOMEONE IS LOOKING CLOSELY AND YOU ARE SHOULDERING THE GUN and using it like a carbine stock, rather than attaching it to your forearm, it would be legally better to have a tax stamp for it. Anything that looks like a shoulder stock will put it into that same category.

Any of the above buffers/brace/stock can be attached to a regular length barrel (>16") upper, legally....if you can mechanically make it fit.

 

very confusing question and details. Terrible OP. Mechanical or legal question depends on the barrel length. Can vs should. Duct and JB weld can do almost anything.

A short pistol buffer (non-adjustable) with a brace with a short (<16") barrel upper = pistol

A short barrel on a long (carbine, adjustable) buffer and attached pistol brace "may" be considered a sbr, IF SOMEONE IS LOOKING CLOSELY AND YOU ARE SHOULDERING THE GUN and using it like a carbine stock, rather than attaching it to your forearm, it would be legally better to have a tax stamp for it. Anything that looks like a shoulder stock will put it into that same category.

Any of the above buffers/brace/stock can be attached to a regular length barrel (>16") upper, legally....if you can mechanically make it fit.

How's it a terrible question if I've never built an AR before? What, do you want me to mail a letter to the ATF and deal with that ****? What do expect someone to think when they go online to a retailer and see pistol brace marked for carbine buffer tubes and ones marked for pistol buffer tubes? No one is using a pistol brace on a legally registered SBR, no one. It wouldn't make sense. So, again tell me how is my question terrible? I even went into THOROUGH detail on everything. Am I jsut supposed to know everything? I must have missed the "How to build your own AR" class in High School and College.

 

How's it a terrible question if I've never built an AR before? What, do you want me to mail a letter to the ATF and deal with that ****? What do expect someone to think when they go online to a retailer and see pistol brace marked for carbine buffer tubes and ones marked for pistol buffer tubes? No one is using a pistol brace on a legally registered SBR, no one. It wouldn't make sense. So, again tell me how is my question terrible? I even went into THOROUGH detail on everything. Am I jsut supposed to know everything? I must have missed the "How to build your own AR" class in High School and College.

 

It is confusing.

There are three different types of buffer tubes (more formally known as "receiver extensions"). They all attach to the lower receiver. The type of buffer tube used does not affect, from a strictly mechanical standpoint, what sort of upper receiver can be attached to the lower receiver.

The legality of different buffer/brace/stock/barrel combinations is where things get really confusing. If you're using a pistol length mil-spec upper, I think you should be OK with any mil-spec lower using either a pistol or carbine buffer so long as you're using a brace rather than a stock.

A pistol-length 300 Blackout upper might have special buffer weight and buffer spring requirements for reliable functioning but I have no idea what those might be.

 

Just buy a brace with it's corresponding tube, a $15 wrench and call it day.

 

Here is some clarifications on the use of the term "other". Other is only used on the 4473 for stripped receivers, complete lowers that have NEVER had an upper attached, and for guns classified as a "firearm" such as the Mossberg Shockwave. The ATF does not use the term other when describing complete firearms. For NON NFA items, it is a pistol, rifle, shotgun, or "firearm". Again the term "other" is only used on the 4473.

And yes if you build an AR first as a pistol then it can go from a pistol to a rifle and back to a pistol. If the AR was built as a rifle first then it must always stay as a rifle.