Hey guys I have probably a  dumb question here  :

I am changing my old SB 15 non adjustable brace out for a  SBA4  adjustable, so do I need to change anything else to make the new brace work ?

The new buffer tube should be longer so  I was thinking I may need a different buffer and spring  ?

Please advise


10.5 Noveske  suppose to be factory built if that matters

I'm thinking the buffer and buffer spring should be the same for either or....  You'll know in pretty short order if it's not.

No idea about the 15. The SBA4 assembly will come with its carbine (mil-spec) 5-position extension. Or you can use any other mil-spec tube though the positions, lengths, etc will likely differ from the SBA4 tube. You'll need whatever weight carbine buffer you prefer and basic spring.

Measure the inside depth of your buffer tube. If it's 7" then you have a carbine buffer assemble, same as sba4. If you have a castle nut and end plate, then that's all that's needed. I mention that because some pistol tubes, like PSA, don't use a castle nut and have an endplate without the index tab. So all you are replacing is the buffer tube. You reuse everything else from your pistol.

thanks so much for your expertise  and I appreciate the knowledge this forum always has . I will check back in here once the new brace arrives  

SB4 kit comes with a spring and buffer
I think

Nope, at least not from SB Tactical. Some dealers may offer a package.

Both braces are typically used on standard length pistol/carbine tubes... meaning, standard carbine length spring fits.

(ETA: To be totally clear... some older SB15 pistol tubes are longer in *exterior length* than the SBA4 carbine tube. They are the same interior depth and use the same spring. So my original statement stands.)

The buffer will be carbine type as well, weight will come down to tuning or preference. A 3.0 oz (AKA "carbine" weight) buffer should function fine. Many prefer H1 or H2 weight buffers on 10.5" barreled ARs, to slow down cycling a bit.

(Some have used the funky Vltor A5 tubes, or 308 length tubes with the SBA4/SBA3 but that is getting a little whacky and custom. Totally not needed... Sounds like you just need a carbine spring and buffer. Done.)

Oh yeah, make sure you have a good castle nut for the install. SB does not include one with the tube. Kind of annoying if building a new lower. Sounds like you probably have an end plate and nut already though.