Broken Bullet -- something I've never seen before

[mehavey]

I started tonight's casting session w/ my PaulJones 457001/540gr bullet for BCPR 45-90 using Lyman #2 alloy I've had in the furnace for some time. Nothing particularly new here except I was going to try a relatively low-temp cast of 650-660° (vice normal 750+) to get the largest diameter bullet I could. Since that was the top end of "Lyman#2" on the thermometer, I thought nothing of it.

Used pre-heated moulds, a 4-count/dipper-in-contact-pour /nice puddle on top to prevent suck-down / and 10-sec wait after sprue hardened.

Ran about a dozen bullets.
Sprue cutting force felt "light" and then this happened:

http://i46.tinypic.com/2m2j482.jpg

Bullet(s) literally broke apart apart upon tapping the handle hinge. Interface looked crystalline/"spongy" and the sprue itself cracked like a sugar cookie. The only thing I'd done prior to this point was throw some sawdust in/followed by a birthday cake candle to flux everything.

I cut the nose off of one of these broken affairs and ran a (Lee) Brinell test that resulted in a 0.059 diameter indent for a BHN = 14.9 ... absolutely dead on Lyman #2 hardness and the same for this RotoMetal alloy in previous sessions

I've got to think this was a differential temperature "thermocline" effect in the mould, but haven't a clue otherwise. Never seen anything like it in 40 years.

Anyone ever see this "sugar-cookie" effect before?

[MtJerry]

Your mold was too hot and it needed a smidge more time to cool before cutting the sprue.

[375RUGER]

Is that a hunk of manmade granite?

[geargnasher]

Your mold was too hot and it needed a smidge more time to cool before cutting the sprue.

This was my immediate thought, but with a 10-second wait after the sprue cooled plus casting with a ladle that seems unlikely. They do look frosted, though, for #2 alloy. Good pic, by the way.

Gear

[mold maker]

That heavy a boolit retains a lot of heat for quite a while. My guess is the metal was still too hot to survive the blow to release it. Same as dumping an ingot too soon.

[bearcove]

With the low temp it might be that some parts of the alloy might not have gone into solution. Pouring an aggregate "concrete", not a liquid.

[runfiverun]

when i open the sprue a tick too soon i see the tear in the base look just like that.
but if you have 5% tin in that alloy and have frosting like that you were running too hot.

[mehavey]

....metal was still too hot preheated mould] to survive the blow...Beginning to think that is the cause -- significantly differential cooling rate in a mould's temperature profile.

This would also explain the driving band being [significantly] smaller than the forward grease groove bands. Driving band took the mould dimensions very hot -- than shrank more than the cooler grease bands.

[mehavey]

man-made granite?
Natural,...from a slab I found in a stoneyard about three years ago and arranged to cut/put in the kitchen.

[bearcove]

[QUOTE=mehavey;1887236] Nothing particularly new here except I was going to try a relatively low-temp cast of 650-660° (vice normal 750+) to get the largest diameter bullet I could. Since that was the top end of "Lyman#2" on the thermometer [quote]

He was casting cold not hot.

[mehavey]

He was casting cold not hot.
BUT.... I had preheated the mould in a "dutch oven" arrangement, and the thinner/top/base portion had gotten too hot relative to the more solid bottom (nose) section.

The pattern is becoming clearer to me. My 30-min preheat needs to be set at a lower temp, and me live w/ the initial rejects to stabilize the top-to-bottom profile.

But that bullet cracking in half was a real Gomer Pyle (http://www.youtube.com/watch?v=J6_1Pw1xm9U&feature=related) momemnt

[bearcove]

It has all the TOO HOT symptoms but you must be cooking the mold to be that hot.

[mpmarty]

Yup dumped before it was cool enough to survive.

[stubshaft]

The frosted appearance is a giveaway.

[jdgabbard]

Again, my opinion is that it was too hot. Boolit wasn't cooled enough to be completely solid when you went to drop it. Another point, you said the sprue cut like a sponge and that sounds, to me, like you were getting torn bases. Which is another sign of not being cool enough. My advice, keep the temp to 700ish, don't preheat your mold as much (or just cast with it cool and throw the ones that aren't up to temp into the pot), and allow your sprue to solidify watching for the crystaline structure on it before cutting. If the sprue isn't giving you resistance when you cut it, you're casting too hot (alloy, or mold). Or you're casting too fast, which doesn't seem to be the case.

[Cap'n Morgan]

The boolit was too hot when you dumped it.

I have a non-confirmed theory (haven't we all?) that the core of the boolits solidify at a progressively slower speed for the larger calibers - even if they look fine on the outside, the core is still not fully solidified. I've done some experimenting using a very large sprue reservoir the size of a shotgun slug, and this large chunk could still be crushed with a pair of pliers some ten to fifteen seconds after dropping. It also seems as a high tin content in the alloy increases the length of the transition period between molten and fully solidified, as seen in the alloys used for car bodywork.

[olafhardt]

Please forgive me if this is a silly coment, I once was involved in calibration. Are you sure your your thermometer is good?

[mehavey]

I'll put two themometers in it today. ;)

But I also think the initially too-hot mould and the differential cooling rate for large bullets as discussed by several posters above is my problem. I'll go at it again this morning.

Film at Eleven....

.

[44man]

Pot temps do not mean a whole lot because you adjust as you cast to keep the mold right. Once the mold gets too hot is where boolits get too small or don't set up fast enough.
The mold has to stay stable or you get hot spots too by pouring too fast from boolit to boolit. Hot spots are smaller or don't fill.
I have broken many ingots like that when in a hurry.
Seems as if a mold only needs to be around 500* for good boolits. You should not make the mold the melting point of your alloy.

[popper]

Normal fracture pattern for #2. Run the pot @ 700F and mould not quite so warm. Fractures when hitting the sprue plate cause the alloy is in transition zone when poured, the core cools slower than the outside but it doesn't make any difference, they alloy is too cool when poured( just starting to mush but doesn't leave wrinkles cause the mould is hot).

[runfiverun]

the mold temp at about 365 would be more like it.
i'd suggest an alloy temp closer to 650 also

[mehavey]

Film at 11... as promised

http://i45.tinypic.com/30cvhjn.jpg

PaulJones 45001 Creedmoor
Lyman #2 at 780°
Dipper in contact full 5 seconds
Sprue cut a full 30 sec after solidify

Results as seen
- No "frost"
- No crystalline layering
- Sprue cut w/ a solid feel
- Driving band a full .4585+
- and a full 2 grains heavier.

[jdgabbard]

Mehavey, good job. Glad you got your problem solved.

[44man]

Film at 11... as promised

http://i45.tinypic.com/30cvhjn.jpg

PaulJones 45001 Creedmoor
Lyman #2 at 780°
Dipper in contact full 5 seconds
Sprue cut a full 30 sec after solidify

Results as seen
- No "frost"
- No crystalline layering
- Sprue cut w/ a solid feel
- Driving band a full .4585+
- and a full 2 grains heavier.
Now you have it, great job.

[mehavey]

After all the screaming and yelling, the lousy batch from last night still shot well at a RamBash warmup today where you only have time for a blowtube between shots.

http://i45.tinypic.com/34o61s9.jpg

Go figure....

[prs]

All is well that shoots well.

prs

[bonza]

I experienced a similar thing a few weeks back, but my bullets were having half of the nose pulled off when the mold was opened. On checking through the rest of the bullets I found some that were split at the nose but hadn't seperated fully. I was using Iso-lead & the bullets were a bit frosty looking, so I expect I was casting too hot. The last batch I ran, at a cooler temp, didn't have the same issues.