I have seen the Aquilla slugs and there are a 6 count of 00 buck loads.
I thought the 1.5" was neat and it would turn my 8 shot pump gun into a 15 shot.
Reading further they say it will only work with the Winchester 1300 guns all others need to be modified.
1.5", 2" and 2.5" were common european lengths.
I have a 2.5" (65mm) side by side and purchased shells from RST for it.
Great guys to deal with. they hunt and shoot. The shells work well.
I have purchased a few cases from them and will do so again when I run out.
But if you are looking for a place to get hulls for your pet projects here is a place to start.
I also spoke with Mec a few years ago and asked if they could set my Size master to 2.5" and they said they could.
They just had to drill another hole. If you look your machines have two holes 2 3/4 and 3".
I think it still may be easier to just buy the few cases a year I shoot from the guys at RST than try to work up loads.
www.rstshells.com/shotshells.htm