Dont think O rings are a problem ,its more to do with the design and build quality , as in tolerances and the surface the oring moves on .Ive worked for companys that build high presure test vessels and they used them every where! ( this still makes me no expert ,il leave that for others). Your ( Shadoh )origanl drawings on the other forum were quite close to Daves thou.
You wont find any more on Dave (Spooky) , ive tried , were in the UK and gun makers hide under BIG bolders here ! rather than be in the public gaze 🙁