Off of the net:
https://www.youtube.com/watch?v=xmv58Z3RZ9c
I assessed the likelihood of hydrogen embrittlement, but to be honest, the main load bearing parts (piston latch, trigger mechanism) are not blued and the rest is under minimal load and force, so I've accepted that the rest is going to be perfectly safe (I probably wouldn't use this for pcp cylinders though).
For the scholars amongst us, this is taken directly from the HSE guidance:
4 The phenomenon known as hydrogen cracking requires both a corrosive environment and tensile stresses to be present.
5 Cracking can occur in two ways:
■■ The hydrogen generated at the surface of a tensile-loaded, high-strength steel can enter the material lattice and embrittle the steel, increasing its susceptibility to failure by dynamic loading (shock loading). This is known as hydrogen embrittlement (HE).
■■ The hydrogen can migrate and congregate in tensile-stressed regions and cause cracks to grow progressively. This is sometimes referred to as hydrogenassisted cracking (HAC).