Is the Magtech 24 guage shot shell brass available there Gert. I make all my 577-450 brass from it.

First trim to initial length (60mm)making sure to polish the mouth of the case as this is where the forming problems often start. The a good anneal is required.
Using Imperial sizing die wax I push the case into the FLS die (from the Lee Set) until the mouth just starts to turn. Care is needed to feel the turn start and to stop at this point.

Some do all their forming in the lee Dies but if you take three 7/8 bolts and drill one with a 15mm hole, the next with a 14mm and the third with a 13mm hole then put a good taper out to the bolt edge and you have your forming dies. I had an unused set of dies and the seating die made a handy start for one of the forming dies but a simple 7/8 bolt was used for the others

Taking the cases that have the mouth turned over and using a length of copper pipe 34mm long over the case and against the shell holder to stop it going into the first (15mm hole) die past the shoulder you have the first step done

anneal again and repeat with the 14mm hole form die

Then with the 13mm hole die

A further anneal and by many in and out steps with the Lee FLS die you get the fully formed 577-450 case. I stop when I start to feel the shoulder and clean the sizing wax that has pushed down against it so you don't get lube dents

Final length trimming to 59.2mm can be done and you are ready to load .
After the first firing I use the 480 Ruger dies to neck size and this makes for the least brass working and longer case life than the over sizing the Lee die gives.

Then you can go play and while I have a smokeless load for plinking you will no doubt want BP
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