Wooo golly!

Quarter inch thick chamber walls. That's the stuff successful hot proofs are made of.

About venting as a percaution for the possible blown primer...
In a conversation with Geoffroy Gourmet some time last year we'd been discussing setting up an R series Darne for hot bore rifle loads. The action we were talking about didn't have the typical gas seal discs on the breech face like the V series guns have, and he noted that a great way to vent the primers was to take a graver and cut a circle around the firing pin holes on the breech face, and from those circles make a cut just as deep (.020" or so) from the edge of the circles running down the breech face to just about where the breech face meets the action flats. The circle should be just about the same diameter as the primer. This way, the little groove doesn't allow the primer to deform into it during firing, but allows a path of least resistence for blowby gas out to the atsmophere -- at pretty much the same spot gas valves would blow via vented pin bushings, without damage to the action. He noted that this was a typical method of venting guns that don't have pin bushings. Since then I've had my eyes out for such detail and have seen a few Liege and Ferlach guns with this feature, some of them had a groove cut connecting the circles between the two firing pin locations effectively giving twice the venting volume to each firing pin.
Pretty simple detail, takes much less time to perform on the gun, and it'll do well to work along with vented striker bushings if that ends up happening in the future of the gun as well.

Looks like this

Marrakai, can you measure the diameter of those firing pins for me and guesstimate the radius in inches on the firing pin tips please?

--Tinker