Ok.. So I have a mk IV webley in .455. It's of course shaved. In the past I used auto rim brass and trail boss to load it using the tb 70% start formula. ( 70% of free case space under bullet ). The auto rim brass is roomy like acp..i really didn't have a pressure concern.
A while back I got a stainless spacer ring that allows normal 455 cases to headspace perfectly. I had no 455 cases..so it sat. Recently found 175 cases.. 75 are hornady Mk-II and the 100 are fioochi and look to be Mk-II cases as well.
They are smaller ( shorter ) cases than acp or AR cases ..etc..
So..im using a lead 160gr bullet..want to make low pressure plinker rounds.. Which is why I didn't go 250-255. I figure lower projectile weight..lower pressure.. Everyone happy...and a paper plate at 5 yds won't care.
Marked case at bullet base. These seem to hold 3.95gr of trail boss. ( 3.9 line just under..4.0..line just over.. Etc on a balance beam ).
So..using 70% and dropping the 2nd digit because I can't set it on the scale anyway.. My start load calculates to 2.7gr trail boss.
Anyone else loading for a mk-IV using Mk-II cases and trail boss see any problems with my procedure?
I know the mkIV was likely a cordite gun..and most lump that into smokeless frame..but I see some sources lump it with black powder frames.
None of my books have print load data..lyman 49,50,51, cast bullet handbook, pistol handbook. None on hodgdon or alliant..none in speer, hornady, nosler or Lee.... None in western.
So I'm down to the trail boss universal formula.
Opinions solicited. I'd love to keep shooting this old girl with real 455 brass