Inclusions?

[carbon_15]

I was casting a few yesterday and had a problem, I havent ever read about. The first thing I noticed was the sprue was very easy to cut....then i noticed the base had hundreds of tiny holes. Pardon the welding reference, but it looked like a MIG weld when you run out of sheilding gas. What the heck causes this?

[docone31]

It is a cracking pullaway.
Essentially, it is just at the point of freezing, not cooled enough. I get them all the time. I just prefer an easy sprue cut.
Never noticed any difference in accuracy.

[Shiloh]

There will often be some porosity in the sprue or on the boolit base. If it is throughout the boolit it indicates other problems; alloy to hot, mold to hot, pour speed, contaminated alloy ect...

There are probably other reasons as well. I also like the ease of sprue cut at these temperatures. Especially on six banger molds.

Shiloh

[454PB]

If you're using a bottom pour pot, it's caused by too much flow, and too fast filling. Reduce the flow or keep the pot level lower.