Isn’t BCM offering there own version of the VLTOR A5 now or is it another manufacturer?
Yes, BCM has an “A5” receiver extension (buffer tube) that is the same as/compatible with the Vltor A5 system, but they don’t have their own buffer; they use the Vltor A5 buffers. The BCM “A5” receiver extension is called the Intermediate buffer System. SOLGW and FCD also have A5-compatible receiver extensions, made by SOLGW.