First of all: I like MP molds. I have 7 & I'm on a group buy for 2 more.
I have a MP 359 Hammer 8 cav. alum. mold that was acquired through a GB. I cast outside & the extreme heat in S. GA prevented me trying it until the 1st cool morning lately. It didn't take long for it to start dropping some keepers & I was able to cast over 800 before the heat shut me down. The batch looked good, but when I finally got around to sizing/lubing I recognized a problem. They all had a pronounced part line & were slightly out of alignment.
I size my Rugers to .359 & my S&Ws to .357. I tried sizing .359 1st & recognized the problem. I figured that the .357 dia. would size out the minor misalignment, but it failed to do so. Also for some unexplainable reason they measure .35650 when sized in the Star .357 die. Everything else comes out of that die @ .357 (?). (all measurements made with a micrometer.....not a caliper).
I stripped the die & could feel a very slight front to rear movement between the 2 halves (very slight.....barely perceptible). There was no light visible between the halves. On a flat surface I tapped each pin & afterwards there is not movement (also no light). The next day I cast a few more & when they were sized I could see some improvement, but not perfect. I stripped the mold blocks again & gave the pins a good tap while positioned on a flat surface.
Today I was able to cast about 75-80 @ a higher heat that produced frosty boolits & about 75-80 more @ a lower temp (shiney boolits). I don't see any improvement & it looks like I've reached maximum improvement. Also note that the mold halves were fully closed resting on a 8" 1"X4" for alignment & the mold handles were gripped @ the very end: past the end of the sprue handle (sprue handle not touched when casting).
I've made some photos so you can understand what I'm up against.
Photos:
#1 & 2: View of the stripped blocks (top side). Initial impression is that they're OK, but the more I look @ them I think I see minor misalignment between 3 or 4 cavities ( maybe an allusion).
#3: average appearance of boolit sized to .357
#4: One of the worst
#5 & #6: close-up view of un-sized boolits showing typical part line.
I'm open to suggestions as what I can do to cure the problem. Also welcome any explanation about the .35650 size from a .357 die when sizing a boolit that starts off @ .359+.
Am I over thinking this or am I being too picky? I have this same design in a 162 gr. Arsenal mold & in a 43-210 Accurate mold & they don't have these problems. In fact I have 2 MP molds of this same boolit both 2 cav. brass: 1 in PB & 1 in GC & they don't have these problems.
Any input is appreciated.
Henry