I have both Matzuo and Eagle Claw's 500BP "little nasty" sickle hooks. Matzuo went thru a short period where their quality control took a sabbatical and the hooks from that time were junk. Unfortunately I had ordered a pile of them. When the issue got resolved the company I ordered from initially stood behind them and I all of the orders sending bad hooks were replaced completely. No all of the Matzuos were bad, only around 40% so in the end I ended up with a lot of hooks of the Matzuo ilk, plus about the same time Eagle Claw came out with the 500 series sickle hooks that are equal in cost as the Matzuos but are about 1000 times nicer hooks to work with as they are very consistent hook to hook. Today it depends on the order...bait shops wanting bulk heads get Matzuos. Individuals ordering on a more custom basis get the Nastys.
In my original reply I mentioned a couple other hook choices in non- sickle varieties but forgot to mention the Mustad 32746BLN. This is a replacement hook for the 570 series and are a very consistent hook throughout all of the size ranges, but the leg length from the bend to the bottom of the eye is slightly shorter than the 570 series hooks. The Mustad is a fairly stiff wire for an Aberdeen hook too.
The molds are quite constant and are cast with the recommended hook choices right into the body of the mold. The eye pocket for each cavity allows a little wiggle room if a person wants to use other hooks and the molds do allow enough room as a rule to use a hook size one larger in either direction of the suggested size, but the smaller the head size WITH the collar, the less options you're going to have. As mentioned by Thembonz, the way the hooks are laid in the mold in the picture shows clearly a pinch at the head/collar merger and if the hooks are laid in the mold with the hook eye snugged down to the bottom of the eye pocket you'll probably start seeing more complete fills. And while I know you've been told you don't need high heat, I cast all of my small head at the highest level using both bottom pour and ladle filling. I don't treat the lead, I don't use any lead that isn't 100% pure, I don't smoke the molds, but I will keep hooks warm if I am casting in a cold garage and on any mold that has the pre-heat chamber on the bottom side I open the mold and set it on a burner of the stove on low to super-pre-heat that sucker....especially is the head size is small and has a collar. I'm living on the edge of the tundra though and this is how I've done my casting, all year long, since I started doing it around 1967. I cast a very few jigs with collars on them anymore and basically all of my small heads are collarless. Small heads like the Bat Jig and Herring head I cut the collars off anyway. But one thing that stood in the way of consistent pours has either related to the hooks, or how they were laid in the mold or when I was using hooks sized outside of the recommended size and the smaller the head size the more critical fit becomes.
Slow down a little and make sure the hooks are in their slots properly before closing the mold and then don't bang it around getting it to the furnace for pouring. Pay attention to how things look in the mold with the hooks before you close it. It doesn't take long to develop a practiced eye for seeing little things out of place.
Here's a little observation I've made over the long haul: Bronzed hooks are more likely to miscast. The black nickel and black platinum hooks have a slick finish and cast the best. Bronzed hooks have the softest temper in the Eagle Claw hooks while the gold plated and colored hooks in the same are the most brittle. Hooks sold as "Aberdeen" hooks can vary in wire size greatly and wire size can affect hot hooks will lay in the mold and how well lead flows around the hooks.
I hope this helps. You're casting little heads and little "things" become big players when doing the small stuff.
