From top to bottom:
Standard carbine buffer tube
PSA PA-10
Vltor A5 – Ignore the rough look. It has Acraglas on it to give it a snug fit for a specific collapsible stock.
Vltor A5 is right at about 7 – 11/16″ (call it 7.75″)
Hard to tell from the camera angle but the PSA PA-10 tube is the same. This has milspec threads and any standard AR carbine stock works on this buffer tube…just like an A5. It does have 6 position vs 7 like the A5 but I’m fine with that.
Standard carbine tube is 7″ for comparison.
ETA: I have also been playing around with the JRC buffer tube which is 8.5″ internal depth. – this link details why: Maximizing BCG Stroke length – “M16 Ultimax”
Note that a Rifle buffer tube has an internal depth of 9.5″