Jackets are soft copper, so they'd give some.
Start loads down a little.
The 12ga Brenekke slugs with locked on base and the USS-S
slugs I test have led to other combinations that I've put
together using different slugs and wads. The object is
60 yd accurate, economical slugs for reloading smoothbores
that in the reloading process we can get more power also.
Like the Lyman cast slugs in thickwall 10ga steel wads,
with the slug glued in and wad cut off even with top of slug.
Then with wad cut even, you load and can rollcrimp perfect.
It makes a real nose heavy combination that is as accurate
in smoothbores, as the expensive 10ga foster style slugs.
Another one is the hollowbase 577 soft lead slugs that Dixie
sells, I put in a thickwall 16ga wad that BPI has. I glue it in
using Goop, a thick glue that hardwares sell. Epoxy works.
Another one is 20ga ga thickwall wad with 54 cal hollowbase
soft lead slugs. All these and others can be loaded for a fifth of
factory for smoothbores, and be as accurate as foster slugs.
And our slow powder loads seal good with wadcups.
Representative one in middlle, 10ga.Slug glued in tight.Ed