Some newer slug ideas coming around. First is Brenneke,
a locked on base ounce slug in sabot at factory speed of
16-1700 or so in 3" plastic.Really go in our 3.5" loads.

Second is Federal Deep Penetrator, 1 oz, copper plated
and a harder lead alloy, than Federals regular slugs.

Third is Dupleks, steel slug riding on a plastic band,
penetrates very well. About 1 1/8 oz.

Seeing the slug base attached deal from Brenneke,
in a sabot I figured out the following.
The idea is the new BPI blue sabot, being undersize for
12ga, is a perfect fit in a 10ga bpi wadcup, The blue has no
cushion on it so it sits in cup ok and a roll crimp works.
Just shaved bottom edge corner and fits bottom ok.
In 32" heavy barrel NEF 10ga, and 10ga 3.5" plastic case,
gets over 2300 at less than mag shotgun pressures
with 440gr slug in blue sabot.I plan on in future to
make a 10ga with rifled barrel, which these would be best in.

If I can find thin wall 10ga wadcup the 12ga bpi AQ slug
would work even better, as it is for smooth bores....Ed

More pictures of the Brenneke and Fed slugs-