AR Rifles and Pistols

[miamivicedade]

Hi All - I was just wondering what the difference is between an AR rifle receiver extension and Pistol receiver extension. I am assuming that a BCM stock would fit on the same receiver extension as an SB4 brace.

The reason I ask is because BCM's site, lists the milspec tube separate from the pistol tube, but the SB4 requires mil spec tube. (https://bravocompanyusa.com/bcm-milspec-carbine-receiver-extension-buffer-tube-6-position/) I am going to buy an SB4 from a buddy (brace only) for $50 but want to make sure i'm following.

This is what the pistol I have currently looks like (so I guess my question is, is this tube milspec?

https://www.gandrtactical.com/BCM-RECCE-9-MCMR-PISTOL-300-BLACKOUT-AMBI_p_2590.html

Thanks.

 

[badkarmamib]

USUALLY, if the rear of the tube is straight 90*, it is mil-spec. Commercial tubes rear slants forward, as in the top is longer than the bottom (Google for pics). Also, a mil-spec tube has the threads machined in, so the tube diameter is smaller than the threads. A commercial tube has the threads cut, so the tube is the same diameter as the threads.

 

[MistWolf]

Commercial received extensions have a larger diameter and will not accept braces or stocks made for a mil spec RE. The BCM in the link you provided has a mil spec RE

 

[Demi-human]

A pistol receiver extension, or buffer tube, is larger in diameter to preclude installation of a rifle stock, therefore no mistake can be made that it is a pistol, not an SBR.
Though @badkarmamib is correct about the extension sizing.

 

[MistWolf]

The receiver extension type does not make an AR a pistol or rifle. If you put a pistol RE on an AR rifle, it's still an AR rifle.

 

[miamivicedade]

The receiver extension type does not make an AR a pistol or rifle. If you put a pistol RE on an AR rifle, it's still an AR rifle.

So I am guessing this is a mil spec tube? https://www.gandrtactical.com/BCM-RECCE-9-MCMR-PISTOL-300-BLACKOUT-AMBI_p_2590.html on an AR pistol?

 

[MistWolf]

So I am guessing this is a mil spec tube? https://www.gandrtactical.com/BCM-RECCE-9-MCMR-PISTOL-300-BLACKOUT-AMBI_p_2590.html on an AR pistol?

Yes

 

[Demi-human]

If you put a pistol RE on an AR rifle, it's still an AR rifle.

That may be. But there is a pistol receiver extension and it is sized as stated.
As seen here.
https://bravocompanyusa.com/bcm-pistol-receiver-extension-buffer-tube-for-ar15-pistols/

And here.
https://www.kakindustry.com/ar-15-parts/buffer-tubes-and-parts

Here too.
https://phase5wsi.com/lower-components/pistol-buffer-tubes/

There are even little shorty ones.

The AR in question doesn’t have one, but instead a mil-spec one.
Neat.

Though I suspect with the upcoming oppression about to be foisted upon us by unelected ATF cronies, this small differentiation will become a much larger issue.
I’m praying it won’t…

 

[wesmonster]

The outside diameter of a milspec buffer tube is 1.145” to 1.150” measured side to side.
Commercial is 1.163” to 1.173”.
A factory BCM lower should be milspec.