+1, at least for your first one. If you do it wrong, the BAFTE will probably still approve it. Then you'll build your SBR/silencer and be in posession of an illegal gun
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I read the case of this happening on ar15.com and that was enough for me to contact guntrustlawyer.com. I don't work for them or anything, but they were really helpful and answered every annoying question I asked them! (probably 20 on my first SBR!)
I've done several applications now and I've got the hang of it now so I don't pester them much any more but it's worth it IMO.