Casting tricks for brass molds

[JonB_in_Glencoe]

Rick,
I gonna add my 2¢
Casting with different molds, that is, different block designs as well as different block materials, often require different techniques, much like you have stated in the OP in regards to Alum vs Iron.
.
For whatever reason Brass molds need more heat. Some brass molds, not all, can develop tinned spots (boolit alloy sticking to the mold) on the block face, near the cavity. It seems that some designs just create hot spots for this tinning to occur. It's a real pain to remove the tinning and it's important to do so, for casting quality. A good patina will discourage this tinning.
.
If you have had a mold, like I have, that has tinned, you will read closely to the discussion about getting a patina built up on the mold. Many casters, who have brass molds, haven't experienced this and likely won't. That is why there is conflicting discussion whether heat cycling, or other patina conditioning is necessary.
.
If this mold isn't one of the troublesome designs, then if you just start casting, you will likely have no troubles. But if you have some trouble, you'll get a lesson in tinning removal and tricks to develop a patina.

[Wheelguns 1961]

Adding to the excellent post by John B, I have had this tinning before. It is very hard to remove. I flux the tinning, and carefully heat the area with a torch, and wipe with a rag. Repeat until all tinning is gone. It is more difficult than it sounds.

[JonB_in_Glencoe]

Adding to the excellent post by John B, I have had this tinning before. It is very hard to remove. I flux the tinning, and carefully heat the area with a torch, and wipe with a rag. Repeat until all tinning is gone. It is more difficult than it sounds.

My tinning removal technique was given to me by Mal Paso, who made quite the informative thread on creation of Patina on brass.
https://castboolits.gunloads.com/sho...-Patina-Recipe
I'm not sure if it's mentioned in the thread or not, but probably is.
Heat the mold to casting temp (about 375-400º), I use a hot plate. Using beeswax and a stick (I use chop sticks), touch the area of tinning with pure beeswax so a little bit melts, then rub with stick. This is challenging to do while mold is hot, and it cools off fairly quickly, so re-heating happens multiple times, until tinning is gone. I mount the mold blocks backwards on handle, so I can access mold faces easier. Have a folded up cotton cloth on bench so you don't damage one mold face, while working on other mold face. THEN...the fun part is cleaning off the beeswax after all tinning is removed. clean as much as possible with heat and cotton cloth and q-tips, then I use MS to clean what remains, then dish soap, Hot tap water, toothbrush to clean the remaining MS residue.

[Rickf1985]

I used the mold the other day and yes, it likes to be hot, REALLY hot. Sometimes the bullets would drop right out and other times I was beating the hell out of the handles to get them to drop. I thought about smoking the mold but holding off for now. I ran probably 200 bullets through the mold but have not had time to go through them for defects. I think I saw some tinning on one of the faces right before I quit so I will have to look for and deal with that. Thanks Jon B for the great writeup on removing the tinning. I think it will be a good mold once I get it dialed in. I had the pot set at 750-775 which is way hotter than I usually cast.