I wanted to try this at some point and I'm not even sure this whole valve setup will even work so this TP is of the same experimental theme.
Its all the 1" tube stuff that bent, went in sideways and I "reworked" as a sick personal challenge. I have fun creating problems and fixing them. I know, it shows but I get to and through things instead of hum and haw.
Anyhow, this TP is a 8mm or maybe .308, a .358, speaking of the brass being repurposed from duds (split cases, berdan primed, used too much lube, etc). I plan on using the extractor groove for an oring slot. The ID will be quite large but I am seeing if I can open about a .40 throat. I failed on this balanced valve and I am still working up to a .46.
Yeah, there was a lot of chatter on the cut as I couldn't use my vice. So I may need to do a little polishing. With a 12mm hole I can always use a 1/2 peek TP if it doesnt work real well. However I am planning on bottoming the case head and press fitting the top into a barrel.
If this works, TP material abounds and will already have a semi workable oring hole (may need squaring).