Saeco Iron mold tinning ?

[JonB]

I have a 1980s vintage Saeco 411, 4 cav (230gr SWC for 41 cal).

I used this mold once, when I first got it (used) in 2011, my notes say it functioned excellent (I was a beginer back then and didn't leave any other notes, and I have no memory of that session). I dug it out just recently (a month ago) for a second session and I had a heck of a time getting the bullets to drop from the cavities. when I gave up and let the mold cool off, then I noticed silver spots (tinning) at the edge of the cavities...the pointy areas of the crimp groove.

I've had brass molds do this, but never had a Iron mold? So today, I heated the mold to casting temp and removed the tinning spots by rubbing the area with a bamboo skewer dapped with beeswax. Once done, I cleaned up the mold, preheated it, and started casting. Casting was going well, bullets dropped nicely. About halfway through, the mold started getting too hot, so I slowed down and also turned on my tiny fan (this mold has fairly small blocks for a 4 cav 230gr 41cal, so that's obviously why it easily gets too hot). Bullets were still looking nice and dropping nicely. When I was done and the mold cooled off, I seen the tinning spots again...I was casting for about an hour or so, 200+ bullets.

the small details
Alloy was COWW with no added tin.
alloy temp was 680º for the session a month ago(according to my notes), I adjusted the PID to reduce the temp to 670º at the beginning of today's session, then lowered it down to 660º when I turned on the fan.

Has anyone else have a Iron mold that gets tinning?
let the comments fly

 

[Pistolero]

It can happen, but doesn't usually do it much.
IME, you can rub hard on the spot with a wooden stick when it is hot to remove
the majority, and then I polish with fine steel wool when cool until I think all the lead alloy
is gone, then hit it with a bit of cold blue. If it blues, you got it, if not scrub some more.

The blue is a good indicator of bare steel/iron and also tends to prevent future tinning.

Bill

 

[Ian]

The blue is a good indicator of bare steel/iron and also tends to prevent future tinning.

Great tip, Bill, that never occurred to me.

Tom sent me a "reject" iron mould a while back to try out for a project and the finish on it appears to be an acid "case-color" job. The bullets just fall out of it. Maybe you guys are on to something.

 

[Pistolero]

Bluing is just a fancy sort of oxidation of the surface. This will generally prevent
the metals from soldering to the "contaminated" surface, and it also will not do anything
if there is still some remaining tinning/soldering on the surface, so a good check to see
if you got it all off with steel wool or other fine abrasive. If it won't blue, it isn't bare
steel/iron.

Bill

 

[fiver]

many molds will form their own bluing in the cavity's just from casting in them.

when I'm lapping lyman molds I re-heat them between lapping sessions so that the blue forms in them.
I then use that bluing color to judge my lap depth.
as soon as I lap it out I have gone about .001 and it's time to make a new lap.