Here is picture of an early falling block for big bores
called the Field I think. Looks like some other
side levers, looks like lever works forward.

And speaking of falling blocks next picture is the
start or 'fixins' so to speak for the next step
up, for my 2bore. Same design as the 4 and 8
bores only wider.

I am now getting 2.25" OD barrel reamed
out to the two bore size.
And a square hole for breach block done
in that hunk of 4130 steel.

Other experimenting, a while back, when I made
my 585 Short HE from Gibbs cases, I also made a
620 Short HE from Nyati case, of the same design,
IE, head spacing on the mouth and extractor.
Using 600NE .620" diameter bullet and 2.7" long case.
Case could be shorter or longer like the 585 one.
Didn't do much with it as its sides were very straight
only .010" taper of both sides together. Whereas the
585 Short HE had .027" total taper both sides. And any
Nyati brass I got, went to make my 585HE cases..Ed