I have been casting for years but just started swagging in the past couple of years. Like many of you I have a home made bullet trap that I recover my projectiles from. Some of these were for my 357 rifle and were made by utilizing 380 brass as the jacket. My pot was approximately 1/2 full of a approximate 95/5 mixture of lead to tin mixture from a previous casting session. I remelted the lead out of the swagged bullets in my casting pot and ended up with a brass looking sheen on top of my lead. When I went to start casting projectiles the lead flow was very slow from my bottom pour pot. I have read many articles where individuals use copper to create more malleable projectiles. My speculation is that the copper/brass was leaching from the brass and mixing with the tin in my lead mixture.
I would appreciate feed back from anyone that may have knowledge or experiences related to this.