Sunken area on bullets

Jeff H

NW Ohio
Thanks, @JonB . I read that back when I was struggling with my first RDO 359-190, like the one in @CWLONGSHOT 's recent post about a new paint color. I fought that mould for a while, and that article offered great insight. It did convince me that I wasn't going crazy, because I noticed a propensity for the several "micro-band" bullets I had exhibited this phenomenon - even the 22.

The article helped with all of them, but didn't cure the 359-190, as it was simply cut too small in the waist. It worked OK in a .355" groove ROssi 92 and is apparently working in the new recipient's Marlin, 35 Remington. The base and front band are big enough that the under-sized micro-bands seem to work like one great big grease groove.

I need to see if I can find so me pics of the gnarly bullets I've had this problem (per the OP) with.
 

Jeff H

NW Ohio
My experience with the small sprue hole in the plate was with a Saeco #221 mold. It did not exhibit the sunken side, but did result in rounded bands. Slightly opening the sprue hole resolved the issue with the BP pot. There does not seem to be any notice that the intimate contact with the BP nozzle and the sprue plate keeps the plate hot so the alloy flows through this choke point easily. Just opening the vent lines resulted in "whiskers" which I found undesirable. My casting was done at about 720 degrees.
I've been happy with the newer vent line style cut in arcs. The only moulds I have or have had, with which I've had difficult venting issues had the old parallel vent lines. On an iron mould, cleaning them out with a sharp scribe was helpful on occasion - get the pint in the groove, somewhere in the middle, and scratch toward the edge. Repeat in the other direction. Aluminum - much more touchy and I hate even messing with them, but have one now with horizontal/parallel vent lines that look like an acid-etched dashed line. Not crazy about the idea of cleaning those up at all.

Funny thing about the new style of arced vent lines is that sometimes only one line connects with a cavity, but it's still enough.
 

popper

Well-Known Member
only one line connects with a cavity that is a problem. understand the manufacturing need but causes uneven venting. There is hot air in the cavity when you start the pour, that goes UP until the alloy pour blocks it. Note you never get wrinkles in the nose of a up-to-temp mould? But you do get them toward the body? Trapped air heats, expands and causes wrinkles unless it has a place to go. Now lets assume a semi-wadcutter design. Nose fills OK, front of band that gets filled traps air under the 'ledge' of the drive band. Air has no place to go quickly.
 

Michael

Active Member. Uh/What
Thank you everyone for all of the good suggestions and things to ponder in about on why and how to resolve. Good stuff.
 

JonB

Halcyon member
After reading that article and all the comments here, it really seems like each mold is it's own dog. Dan seemed to only be having this issue when casting Heavy large caliber bullets, but maybe that's mostly what he casts?

I hadn't heard of the tin rich theory before, it'll be something I try next time I tackle the long skinny 30 cal, which is the only time I see SDS, with my casting preferences. I use 94-3-3 for pretty much any Rifle bullets, so Maybe I try Straight COWW next time.
 

fiver

Well-Known Member
or a 50-50 mix.
we used to call the tin thing tin poisoning and it was with the bigger bullets, or the long skinny ones.
bottom pour exasperated the problem, and IMO part of it was allowing the alloy to flow through the air.
 

Loren

Member
I have a nose pour hollow base mold that gave me fits with a shrink problem up in the base. What finally got me better results was slowing the flow from my bottom pour pot.