Old photo, that I posted in cast pic of the month back in 2013.
http://castboolits.gunloads.com/show...-Imperfections
OK, I've been casting for 4 years.
As like many of us newbies, I am continually seeking to improve my technique. One issue I have had, mostly with long rifle boolits, is shrinkage. A few different examples of such are shown above.
I've asked questions about this, at least a couple times since I started casting. I've tried the suggested answers and while they may have been good ones, they weren't my solution.
For me, this shrinkage issue was about as random as it gets. sometimes it seemed like it was one particular cavity of a mold...so I'd try changing the order that I'd pour the cavities, many times it helped, but the shrinkage issues would always return sooner or later.
I tried different alloy formulations...more Tin, then Less Tin. Once in a while the problem seemed to get solved...only to show up in the next casting session ???
I obviously tried different alloy temperatures and casting faster (to raise the mold temperature) as well as casting slower and using a fan to cast with a cooler mold and getting shiny boolits. It seems each time I'd make a change and go with it, the problem would go away...only to show up after I'd get into a rhythm ...as soon as I'd get comfortable, the shrinkage issues would pop up and get more frequent.
I think I found the solution last summer. If you clicked on the link at the top of this post and scrolled down to #8 to see my March 2013 photo submission, you'll see I edited the text in August 2014 with what I figured out this summer.
I wanted to make a grand post like this back then, but I thought I solved this problem so many times before, I was hesitant, for fear I was wrong again.
So now with several successful rifle boolit casting sessions under my belt, I am comfortable announcing the solution to my problem.
The Solution:
Pouring as large of a sprue puddle as reasonably possible.
My problem I had to overcome to resolve this:
I'm sure I've read about pouring a large sprue and I'm sure I've been told that as well, when I asked about shrinkage in the past. But what it always came down to is...when I'd get into a comfortable pouring rhythm, I pour a smaller and smaller sprue...so as to reduce the amount of alloy usage per pour which should yield more boolits per pot of alloy. I needed to reprogram my brain. More perfect boolits per pot is better than just more boolits per pot.
The Photo below showns my most recent casting session using the NOE 358009, these have not yet been sorted, you may see a couple flaws here and there. NOW, if I have poured small sprue puddles as I did a year ago, more than half would have to be culled.
That mold WAS probably my most troublesome when it came to shrinkage...I suppose it's ratio of length to width, is the greatest of all of the boolits I cast, which would probably exacerbate shrinkage from a small sprue puddle.
I just thought I'd share this, because it took me soooo long to figure it out, even though the solution was always close at hand.
Good Luck,
Jon