very interesting ,
i like your scientific approach fps ! just wondering how you caculate it (probably with the distance) ?
where did you get the new barrel 6.04mm ? link?
could i use the complete metal tiger barrel from ebay to shoot ?(good diam.?)

think i have cross a post of you on the other site (ket).
so you don t buy the whole holes theory[&:]

will try to search and look back your postings.

for the breach problem that you`re experiencing ,
can i suggest ,forge it with aluminum ,it is such an easy material to work.
or
making a cast ,with a putty then,
go purchase a can of fiberglass(paste type) with strings of fiber(no sheets) apply the waxpaper on your new moulds so the fiber wont stick to the moulds once hardened ,poor the f b paste.
fiberglass will absorb the stress.
and of course ,make the new part thicker on one side.