I thought i would do a post on making mongoose brass. I stumbled on something when making brass for the ocelot. 
when i was forming mongoose and the first ocelot i always had a little bulge at the shoulder now it dont hurt anything and it is because the case actually blows out there so it is unsupported in the die when forming.

well i wanted to set up to make brass in bulk so i had a couple 223 trim dies for my dillon rt1200. i took one of the dies and modified the neck area to work to trim mongoose. First i took and found an end mill i had laying around it was a 1/2 inch end mill that had the cutting teeth on the sides of course but also on the flat bottom. It fit perfectly in the top of the die so as you can see in the first pic i counter bored the die down about .120 then i opened the neck up to .265 or so that way all the die is doing is trimming this is important because i set my tool head up on the 650 with the mongoose die in station 1 with expander so it runs through the die sets shoulder and expands. then in 4 i have the trimmer. i hold the die a little off the shell holder because i don't want to mess with the new shoulder just formed. and i set to trim to 1.693 that way when fire formed them come in pretty close to 1.69.