Frosted void in bullets?

[Jumbopanda]

For some reason a lot of my 311365 bullets come out with a frosty void on the ogive. The rest of the bullet is filled out nicely and the edges are sharp and clean, but about half the time there will be this strange void. I've tried a wide range of pot temperatures from 650F to 750F, the mold is run hot at around 400F, and generally the rest of the bullet turns out perfectly fine. If it weren't for these voids, I'd say my reject rate would be less than 5%. The voids are very easy to spot because they are always frosty, even though the rest of the bullet is not. There are no imperfections in the mold that I can see. What might be causing this?


Here's a picture that shows what I'm talking about:

76578

The curved red line represents the void. This picture is a bit exaggerated for illustration purposes as the actual voids aren't quite this deep.

[detox]

Mould is too hot. When i cast my outside mould temps are around 230-250. I check with small infra red thermometer.

May be a venting problem also.

[runfiverun]

try tipping the mold the other way.

[detox]

What alloy are you using?

[high standard 40]

I've had that same issue with an RCBS 7MM 145. I decided that the mold was too hot so I ran the mold cooler and the problem went away.

[Gtek]

Welcome to the fun! If it were me I would clean and then clean again the mold. That spot looks to be about where the slots are cut for handles and your cadence and mold temp may have you on ragged edge of something it does not like. Mold temp and pot temp are only two of the many involved with Happy Land. Bottom pour, Ladle, side pour, center pour, drop pour, you did not say. Maybe start out with mold cooler and cadence up to temp. Every mold, every alloy, all I can do is guess from here. Gtek

[RobS]

http://www.mountainmolds.com/shrunken.htm

is a possbility

[KYCaster]

Two cavity mold?

Void at the parting line where the cavities are close together?

It's a combination of venting and heat....or specifically, a hot spot. Not enough vent to carry heat away from the point where the lead stream contacts the mold.

Improve venting by stoning the top edge of the mold blocks as described in the Lee-Menting sticky. I have one mold that wouldn't shape up till I filed a vertical vent midway between the cavities.

Also try "swirl casting". Tilt the mold slightly to one side and direct the lead stream off center so it swirls into the gate like bath water draining out of the tub.

Hope that helps.
Jerry

[Jumbopanda]

Guess I still have a lot to learn about casting...the number of variables involved just seem endless.

Some info:

The alloy I'm using for this batch; a voodoo mixture of lino, wheel weights, range lead, and foundry type, should be very very close to 92/2/6 if my calculations are correct. I'm having more problems with this alloy than I was with my 8-1 WW/foundry type alloy.

The mold is a NOE 311365 plain base five-cavity. Another issue I've encountered was little bits of lead building up around the tips of a couple of cavities, eventually resulting in finned bullets. I did not have any finning issues since reducing the pot temp to less than 700. I think the mold has to be kept pretty hot when using a low pot temp, otherwise I'll get wrinkled bullets.

[detox]

Guess I still have a lot to learn about casting...the number of variables involved just seem endless.


Linotype will fill the mould LOTS better...especially when casting smaller rifle boolits such as .308 and smaller. RCBS and Mike Venturino suggest using only linotype for such.

When casting with linotype a pot temp of 650 and mould temp 230 will cure your problem.

[Jumbopanda]

I've experimented with a variety of pouring techniques and haven't found any consistent way to avoid the issue. I enlarged the pour spout on my Lee 4-20 to 0.101", which allows for much faster pouring than the original hole size, and I can fine tune the pour rate with the adjustment screw.

I've tiled the mold, poured straight down the hole, poured on the sprue plate, increased flow, reduced flow, held the mold up to the spout, flooded the sprue plate, but nothing seems to indicate that any of these techniques will produce consistent results. The larger spout SEEMS to reduce the severity of the problem a bit, but I have noticed that there is still some inconsistency in the ogive diameters. When the pot is full, I have to adjust the valve down a little bit, otherwise the stream will be too aggressive and cause splashing instead of forming a neat sprue puddle.

After casting a batch of 200 or so bullets, I measured them and found that while the driving bands are generally within 0.001" of each other, the beginning of the ogive ranged from 0.303" to 0.307". I'm GUESSING that this won't be too bad for 100yd shooting, but I can't help but wish for better results. The bullet weights varied by up to 2gr, but the vast majority were within 1gr of each other.

[Jumbopanda]

Well, after banging my head against the wall for a long time, I finally figured out that the problem was simply the alloy. My findings were consistent with those of Mountain Molds. This mold does fine with straight wheel weights and even better with straight linotype, but it seems to hate anything in between.