Last year I desired a 45-70-405 mold with a defined crimp groove, for my 2003 vintage Marlin 1895GS. I saw nothing on the 'commercial' market that tripped my trigger. It was then necessary to obtain a chamber & breach impression to see what I actually have to receive some future magic boolit. I cannot afford those exotic low melting temperature alloys & didn't feel I could trust their dimensional stability, after some articles I read, so, after a few calculations I:
-- obtained some SWW's [stick on wheel weights] which are reported to be 99% [or so] pure lead, a propane torch, a small aluminum
funnel, needle nose pliers, 3/8" dia. rod, 3/8" dia. rod or dowel @ barrel length, hammer, helper/3rd hand & an empty rifle case
-- drilled a few 1/2" dia. holes, about 3/4" deep in a scrap 2x4,
-- drill or fashion a 5/8" dia. hole to hold the rifle case,
-- wrap aluminum foil around a 27/64" drill shank & fashion a "cup" about 3/7' deep,
-- place your new aluminum cup into the 1/2" dia. hole & gently enlarge it with a 15/32" drill shank,
-- melt lead into these "slug" molds,
-- heat the rifle case's top half to a red heat & cool with water/wet rag [this annealed case will better form to your chamber],
-- melt lead into your case, stopping 1/4" from full,
-- force one of your suitable lead slugs into the case & taper its front,
-- place your barrel muzzle down into an old boot [a cushion],
-- place this "chamber slug assy." into receiver & with the steel [wrapped in tape] or brass rod, hammer down onto the case, thus forcing
the slug into "battery" until you can close the breach,
-- now open the action, & tap the "chamber slug assy." from muzzle, into the receiver,
-- measure diameters [micrometer or dial caliper], dutifully record & gently wrap this valuable "tool" for safe keeping.
The result was not perfect, but did yield sufficient areas for good data taking.
Looking back at all these steps now, I'm surprised I accomplished this arduous task. Truth? It was fun to figure it out & help myself to obtain a needed piece of information. Since then, I've read where some use a bore dia. + slug & pound it in from the muzzle. That seems to me as not a great idea, stressing the bolt, etc.
Best regards & play safe,