Frosty.......

F

freebullet

Guest
Wondering, if frosty bullets (appearance in texture, not from cold...for you pun lovers of the group) happens at a given temperature with each alloy, ect. I never really thought about this much. Definitely notice it more with high antimony alloy.

What is your experience with it? Any temperature consistency where it happens, with certain alloys? Do you actually prefer it for certain purposes?
 

fiver

Well-Known Member
it's the antimony causing it.
and it's mold temperature not alloy temp.

anyway there is frosty and there is frosty and there is another step beyond the white frosted galvanized round corners second one.
it will actually give you beautiful almost zinc galvanized looking well filled out bullets that take about 2 minutes to solidify in the mold.

the first one is a satin color oxidization of the antimony on the surface of the bullet.
they get there by time allowing the antimony to flow to the surface, this is why the bullet is filled out so well.
tin does basically the same thing [and at a lower temp] only it hides it by not oxidizing.
 

Ian

Notorious member
With 2% or higher antimony and very little tin, I run mould temp into the twilight zone just past the white fuzzy edges phase because that us where I get the most consistent weights and sharp definition. Come to think of it, I run all my antimonial alloys at that point unless I'm trying to fatten the bullet, in which case I run the alloy heat up and slow down the casting and use a fan to quench the sprues. I let the bullets cool in the mould only to the point where they don't break when hitting the towel.

The only frosty that's bad is the kind where the mould is so hot the bullets won't set and they start leaving metal in the moulds. Bullets cast this hot will appear rough and dull like broken cast iron. The other, less extreme frosts such as I like to see leave a crystallized antimony wash which can be wiped off with a twist of a dry rag to reveal a perfectly shiny surface underneath. If the alloy has a balanced amount of tin, the frost will be smooth and satin due to the fine-grained Sb/Sn intermetallic bond. If mostly antimony, you get that faceted, battleship camo look like electro-galvanized steel roofing (not galvalume). The appearance is all about mould temperature, as Fiver said.
 

Pistolero

Well-Known Member
IMO, frosty is good. Those are the really sharp bullets filling the mold perfectly.
At least with WWt alloy, which has a good bit of antimony.

Bill
 

Bret4207

At the casting bench in the sky. RIP Bret.
I agree with the above. Frosty bullets never bothered me at all as long as it was a uniform frosty-ness. If the appearance bothers you a quick twist with 4/0 steel wool on the exposed portions after loading often gives you a shiny bullet. Reduces diameter very slightly too, so...
 

L Ross

Well-Known Member
fiver and Ian, are you saying that there is a point beyond the rounded corner, burnt looking bullet in the mould, that will produce a well filled useable bullet? When I get those over cooked looking, rounded edges, I start cooling the mould/sprues longer in the air flow of a fan until I get back to sharp cornered, frosty bullets. The light frost, knife edged bands, with perfect detail is my favorite bullet for alloys with antimony in them. The situation that really drives me nuts is with multicavity moulds where one or two cavities start to get too hot when the other two, three, or four are just right. Then I start playing around with the filling sequence, skipping the hot cavity, and all sorts of juggling nonsense. I have come to the conclusion that two cavity moulds are the easiest to deal with, especially in aluminum/
 

Ian

Notorious member
The effect I typically observe as the mould heats is first shiny and not filled, then shiny and mostly filled, then for a split second there's shiny and sharp, then the edges start frosting white and shrinking out of the corners, then a light grey frost comes over the whole bullet and it begins to get sharp again, then slightly heavier frost that precipitates after the bullets have cooled for a minute or so and the edges are razor sharp, then the whole bullet becomes dull grey and sandblasted-looking.
 

L Ross

Well-Known Member
Ian, have you ever observed the burnt edge look? Or hot spots that refuse to fill in until the mould is cooled a bit?
 

Ian

Notorious member
"Hot spots that refuse to fill" almost always respond to an increase in casting pace/heat. If increasing mould temperature doesn't fix it, then just about the only remaining cause is a problem with venting or pour technique.

It's been my observation far and wide watching threads on these boards that most casting problems (attributed to oily moulds or zink contamination) is actually lack of heat. Much of the time when people see the first signs of "frost", which shows up on the band edges first while the rest is relatively shiny, they immediately cool the mould. Why or where that got started I don't know, it's like people are afraid to get their moulds hot or are unaware of what a truly hot mould casts like. Others often recommend that the pot temperature be raised and mould cooled to alleviate the "burnt edges" problem, but that is the exact opposite of what my experience tells me to do.
 

fiver

Well-Known Member
yep I generally drop my alloy temp about 10-15* at that point and punch through by kicking up my pour rate a little for a few casts.
once I get there I settle down into cruise mode and just take it easy casting going a nice smooth 3 pours a minute or so.

the uneven heat thing comes not the filling sequence so much but from letting the mold sit under the pot while cooling.
there can be a very drastic temp difference between the outer edge facing you and the edge back up under the pot especially if there is a slight amount of air movement in the room.
filling the back holes first and pushing them in to the hot zone back there just brings more heat into the picture.
I learned long ago to pull the whole mold out from under the pot to rest while I wait for the alloy to time out.
when I open the mold the alloy is still bright and shiny, as it sits on the rag for about 10 seconds it flashes over to a uniform grey color like it just oxidized.


those white hot spots are just the hot alloy hitting the mold over and over again transferring the most amount of heat to one spot.
if you do that over and over again it will even cause shrinking on the bullet right there as the rest of the alloy pulls the heat away from that spot when it tries to cool down.
 

Ian

Notorious member
I learned long ago to pull the whole mold out from under the pot to rest while I wait for the alloy to time out.

Yes, very important lesson there. If anyone has watched Lynn's videos they will notice he fills the mould quickly and then rests it on a board away from his furnace while the sprue sets. That's a pro caster at work.

Along the same lines as hot spots, cold spots develop as well, and cold alloy in the bottom-pour spout too. When wrinkles appear on a bullet that's otherwise well-filled, many times one can identify it as a splash from the initial dollop of alloy hitting the nose and freezing on the mould wall before the cavity has filled. This is one of the ways to tell by looking at their bullets if someone is bottom-pouring or ladle-pouring.
 

fiver

Well-Known Member
Lynn uses a set up super similar to mine.
our stands are a bit different but watching him cast is like I'm watching myself.
 

L Ross

Well-Known Member
I have never run into the "burnt" looking spots in iron or mehanite moulds, only aluminum. I don't leave the mould under the pot, I usually just hold it in my hand waiting for the sprue to jell, then move in front of the manicurist fan and wait for the sprue to frost before opening the mould.
For me, the most difficult moulds to work with are the 4, 5, and 6 cavity aluminum moulds. I was speculating that the heat transfer was different in the center cavities where there is hot alloy on either side as opposed to the end cavities that have solid aluminum to act as a heat sink.
 

RBHarter

West Central AR
I've found that the Lee 6s cast 3 different bullets sometimes 4 . Generally 1 about 2 gr light , 1 about 1 gr light and 4 about 2-5 gr heavy but consistent at whatever number that is . I've found the lightest to be on the handle end and the second lightest to be on the hinge end of the sprue plate . My best solve has been to just ladle pour slightly up hill from the hinge to the handle . The larger cal seem less effected and honestly for my typical shooting 1-2% doesn't matter in 38/357 , 40 , and 45 . The 5s from NOE seem to drop one about 1 gr light on the sprue plate hinge end without regard to the direction of pour as long as the handle end rests on the pot during the pours 10 on 2 off or so . That monster H&G #130 cast 195.5-196.2 and doesn't care as long as the trough is full .

I have a 3 cav aluminum NOE 460-543 (version of the 458132 @535) I can't find a measurement difference . The others run within 1.5% except a 287-150 Hunter that I've fought since day one ........I'm sure it's operator error but I'm yet to get 5/5 keepers from one pour . Without fail it has a cold sprue on one end or the other . It's been a long time since I cast it , maybe I'll try the pour uphill thing again .......
 
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fiver

Well-Known Member
your heat transfer is different.
and I think the handles have an influence on some molds too.

heat transfer is an odd thing, it's is always in motion but not always constant.
I have noticed my results are best when I make long sweeping non stop consistent runs of bullets.
I think the advantage is the heat has made it's way out to all of the edges of the mold and isn't pulling it away from the center at the same rate as a mold that hasn't done that yet.
this allows me to add less heat each time, but maintain what is there easier.
 

Ian

Notorious member
If I'm trying to cast a run of consistent, high-quality rifle bullets (such as from my Lee 6-cavity 311041 improved copy), I break out the mould oven and soak it for a minimum of half an hour at 400°F. The handle tong heat sinks cause irregularities in the middle two cavities for about 20-30 pours, or nearly half a pot of alloy, so I pre-heat the mould and handles to minimize the culls.
 

Creeker

Well-Known Member
the uneven heat thing comes not the filling sequence so much but from letting the mold sit under the pot while cooling.

Sure enough.

there can be a very drastic temp difference between the outer edge facing you and the edge back up under the pot especially if there is a slight amount of air movement in the room.
filling the back holes first and pushing them in to the hot zone back there just brings more heat into the picture.
I learned long ago to pull the whole mold out from under the pot to rest while I wait for the alloy to time out.

Sure enough.

Lynn uses a set up super similar to mine.
our stands are a bit different but watching him cast is like I'm watching myself.

Now I know there are at least two.