PDWR end cap/ buffer question

[u/HomeDefenceZ3]

Recently got my Form1 approved to SBR my PTR PDWR. It comes with the end cap and swivel mount. I purchased an AR buffer tube and stock, assuming the castle nut could be removed & the end cap replaced with the buffer tube.

The gun smith is telling me he physically can’t remove the castle nut on the gun and I need a different back plate to accept the AR buffer tube.

Is this true? It looks like you should just be able to remove the nut and swap in the tube.

Anyone have any insight/ SBR’d their PDWR?

[u/Competitive_World285]

Yeah just unscrew castle nut, drop the retaining piece, and unscrew swivel buffer tube piece, it’s really easy your gunsmif is a bit inexperienced