Which extended buffer tube for SBA3?

[SKelt]

I have decently long arms so the stock mil-spec buffer tube on my recent grendel pistol build is shorter than I can comfortably run with an SBA3. For an extended buffer tube I have a couple questions:

1) Which buffer tube should I target? I prefer reliability and not violating the brace LOP limitations set forth by the ATF (13.5" fully extended is the limit from my research)

2) Will I need a different buffer spring and buffer with a recommended buffer tube? Fairly sure I will need a different spring, not sure about buffer.

Thanks for the help

[A5BLASTER]

If you put it on an extended buffer tube you will be violating the rules, i think.

It clears states it can't be modifiyed. The sba3 is designed for mil spec length carbine buffer tubes. Putting it on an extended buffer tube, I think would be considered modifying it.

[Bigs28]

Don't alter it. Use it as purchased

[Lastrites]

Yet another gray from our friends at the atf, the latest info stated using a standard tube and said that the tube would have to be fully functioning as in prohibiting extended tubes such as the KAK Supertube which has solid core of at least an inch at the rear of the tube that essentially does nothing but increase the overall length of the weapon. Nothing was mentioned and shouldn't be prohibited using a Vltor A5 or a regular rifle extension as they are fully functioning so those should be able to be utililzed. The other end of the contention is the previously stated LOP measurement which was not to exceed 13.5" this may cause if using one of the longer tubes. I believe I recall seeing a Vltor tubed pistol brace and it was just short of the 13.5" mark.