SBA3 buffer & spring question

[FN USA]

I've been considering converting an AR with rifle stock to an SBA3 brace to make a pistol. What buffer and spring would I need to ensure it operates properly? Could I just buy a longer adjustable buffer tube and use the original buffer and spring? Internet has a bunch of ideas and all are different.

For reference, current rifle buffer tube is 10". SBA3 buffer tube is 7". I'm not sure what spring and buffer is currently in my RRA lower.

Pics to make you look

 

[roscott]

Hopefully the barrel on that rifle is still 16+. Changing the stock to an arm brace does not make a rifle into a pistol. If a receiver is ever used as a rifle, it is always a rifle according to the ATF.

 

[FN USA]

Roscott, I am aware, any ideas for the question above? I'm using a new stripped lower I had laying around.

 

[BR8818]

Just make sure your LOP is under 13.5"

What length barrel, caliber, gas length? That will dictate your buffer weight and spring.

 

[T-DOGG]

You need a mil-spec diameter (not commercial) carbine length buffer tube, carbine length buffer spring and a carbine buffer for the SBA3 brace. These would be the same components that come standard on an AR-15 with a collapsible stock (like the M&P15 Sport or Colt LE6920 for example).

The rifle length buffer tube uses a rifle length spring and rifle length buffer. This will not work with an SBA3 brace, because the rifle length system is not designed for a collapsible stock/brace, it's just a round tube that was made for a fixed non-adjustable stock like the one in your picture.

 

[Old Dog]

Just make sure your LOP is under 13.5"

Would you please provide the ATF or NFA or GCA68 reference for this requirement?

 

[FN USA]

Thanks for the replies,
I'm thinking 10.5" with carbine length gas tube in .223/5.56.
I'm worried about stressing the gun with the rounds I typically put through a weapon. I'm thinking an H2 buffer with enhanced 17-7 spring? Bking firearms has a good sale on the combo blue lots right now

 

[EricG]

Gas system length and gas port size would dictate buffer system.

Sent from my SAMSUNG-SM-G930A using Tapatalk

 

[T-DOGG]

Apologies, I completely misunderstood the original question.

 

[BR8818]

I run a h2 and sprinco blue in my 13.7" and 10.5" they're both pretty soft shooters.

 

[Cameramonkey]

Hopefully the barrel on that rifle is still 16+. Changing the stock to an arm brace does not make a rifle into a pistol. If a receiver is ever used as a rifle, it is always a rifle according to the ATF.

Actually, my understanding (IANAL) is that only applies to what is listed on the 4473. According to the ATF and clarified in I THINK memo 2011-4 any modular pistol platform can be converted to a rifle and back.


4473 disposition:
Rifle-always a rifle
Pistol-can be switched to a rifle and back at will.
other (stripped lower)-Once built as a pistol, it can be switched to a rifle and back. (some also say it doesn't matter which you start with since it originated as "other")

Some have taken the ATF memo above to mean that what its transferred as is now irrelevant. But (once again, IANAL) I could not find any language to negate the original rule that says "once a rifle, always a rifle."

Edit: found it... 2011-4 memo:

https://www.atf.gov/file/55526/download

 

[BR8818]

Would you please provide the ATF or NFA or GCA68 reference for this requirement?

https://www.ar15.com/forums/AR-15/LAW-Folder-GTG-/122-735576/

That's a link to an "opinion letter" on arfcom to some brace company supposedly they sent out private opinion letters to companies that manufacture braces. I know they also tried to prosecute a guy in Ohio for his length of pull on a maxim defense brace but he won.

Do you know more about it? I have one over 13.5" I wonder about.

 

[FN USA]

I went ahead an ordered the BKing Firearms Sprinco enhanced spring and H2 buffer. The pistol shoots like a dream now!

 

[BR8818]

Same setup I'm running it's a great combo.