sprue shrink

[44man]

Cast some today and took a picture of sprue shrinkage. Notice how little there is. Nothing more the the sprue itself, nothing going to the boolit. Bad picture, I know, cheap camera. Don't feed the boolit from the sprue. 111025

[TenTea]

Always pour a generous sprue!

[Calamity Jake]

YAP I Always pour a generous sprue!

[Le Loup Solitaire]

If there is not enough of a sprue (puddle) to feed the shrinking/shrinkage then you will probably get voids/holes under the bullet base and they are usually off center so you get a weight off center problem that causes poor accuracy. Some casters go back and forth with the pour stream at least once---sometimes twice to really "puddle" generously. Sure..it makes for some sloppy pouring/sprues, (that are going back into the pot anyway) but there is plenty of extra to feed the shrinkage. Another trick used by some folks is to arrange things so that the blocks can be dropped about an inch with the sprue still liquid onto an ingot underneath so that the "jolt" will cause the liquid sprue to better fill out the cavity. I helps a lot with some molds that have "an attitude"....and some do! Some of this may take a bit of practice, but you get used to it. Neatness and perfect pouring form are nice, but the object is to get well cast bullets that shoot well. A gentlemen of some fame in the bullet world named Guy Loverin once said, "Watch the quality and not the clock". LLS

[osteodoc08]

I pour a very generous sprue. It also helps to have a sprue plate up to temp too. My first few pours on a heated up mold I nearly cover the sprue and let it heat soak 5-10 seconds or so. This is after even being flipped over on the sprue plate heating on the hot plate. When the sprue plate is up to temp and mold is up to temp, you should see a divot where the hole is in the sprue plate. This is from where the cavity draws from the sprue to make fill out of the bases.

[country gent]

I have "vented" my sprue plates on my rifle molds. I normally pour bullets in the 40 / 400 grn and 45 /500-550 range. With the vented plates I no longer pour for a sprue but pour a full ladle to empty and once the mold is up to temp the sprue is very consistant in size. This keeps the bullets base hot longer allowing for off gassing and better flow. My last batch of 300 40s went 402.8 to 404.4 after culling visuals out. By pour a generous sprue the base is kept hot longer and flow is improved

[44man]

I feed the boolit with molten metal from the ladle. Keep the ladle in contact long enough and the boolit will need nothing from the sprue.
Now you bottom pour guys need more sprue.

[Pb2au]

It took me a bit of casting to get my head wrapped around how important the sprue was. Like many, I would watch in fascination as the sprue puddle would depress and feed into the mold.
one day it kinda hit me that this was not a good thing. After that I revamped my technique and my quality went way up.

[44man]

It took me a bit of casting to get my head wrapped around how important the sprue was. Like many, I would watch in fascination as the sprue puddle would depress and feed into the mold.
one day it kinda hit me that this was not a good thing. After that I revamped my technique and my quality went way up.
Exactly, you got it right. The sprue can set before the boolit. That will limit what you can feed unless you keep it molten. To try and remelt a sprue is still bad. It is too late.
My time to tip off changes with boolit size. I cast a pile of 420 gr, .475 boolits yesterday without a single reject. Mold is preheated to 500* in my little oven on a hot plate. First boolits are perfect.
Even 560 gr boolits or slugs for a shotgun are no problem.
FEED your grass guys! Not my yard full of weeds though.

[shredder]

"Don't feed the boolit from the sprue"

Hmmm got my attention there! Such a simple statement with so much experience rolled in, I had a good think about this.

As a bottom pour guy I too pour very generously. You made me stop and think about what I "know" about feeding from the sprue. I never stopped to question why the rather extreme shrinkage to the huge sprue puddle I pour was happening. Another tequnique upgrade coming.

Always learning something new around here!

[osteodoc08]

So what teqhnique are we suggesting to stop the sprue divot? I've tried pressure casting and didn't really
notice a difference. I try to
hold weight to +-1% for my
general use stuff. If im
uskmg it for hunting, ill weight each individual boolit
and select +-.1 grain. Never really
noticed a huge difference in practical
accuracy with typical handgun ranges (under 100 yds).

[country gent]

I dont pour a sprue but pour the hole ladle full of lead into the sprue hole slowly and evenly. My plates are "vented" and extra runs off but in the extra time bullet is molten that much longer allowing for base fill out and gases to be released. Its not a issue ladle pouring as I hold mold over pot and it flows back into the pot. Keeping the cast hot helps tremendously. With a bottom pour mabe 4-5 secs of pour time after filled allowing excess to run into a catch pan?

[osteodoc08]

I dont pour a sprue but pour the hole ladle full of lead into the sprue hole slowly and evenly. My plates are "vented" and extra runs off but in the extra time bullet is molten that much longer allowing for base fill out and gases to be released. Its not a issue ladle pouring as I hold mold over pot and it flows back into the pot. Keeping the cast hot helps tremendously. With a bottom pour mabe 4-5 secs of pour time after filled allowing excess to run into a catch pan?

Ok. I am very generous with my sprues and they will often flow over the sides, especially with y small lyman 2 cavity molds.

[MT Gianni]

I dont pour a sprue but pour the hole ladle full of lead into the sprue hole slowly and evenly. My plates are "vented" and extra runs off but in the extra time bullet is molten that much longer allowing for base fill out and gases to be released. Its not a issue ladle pouring as I hold mold over pot and it flows back into the pot. Keeping the cast hot helps tremendously. With a bottom pour mabe 4-5 secs of pour time after filled allowing excess to run into a catch pan?
I have one RCBS mold that will not cast acceptable bullets unless it has a 3 second pour over from the bottom pour pot. No other RCBS old has this quality but this one does. When you find out what they need write it down.

[mold maker]

I too am confused, although I think you all are saying the same thing in different terms. Since the sprue is the only place the boolit can draw from, during shrinkage/cooling, aren't you all saying that, keeping the sprue and plate hotter/longer, is the way to stop boolit shrinkage, and solve fill out?
The only other aid I know of is to very slightly bevel the top mold edges to provide extra venting, and make sure the sprue plate isn't too tight. That along with proper alloy has always solved my problems.

[44man]

Yes, heat but I ladle pour and use the molten metal and heat from the ladle to add lead as the boolit shrinks.
Nothing to do with venting, just lead feed.
It is OK to keep pouring at a cavity to keep the sprue melted for the boolit to get more lead. Just messy.

[Cap'n Morgan]

It is important to realize that the shrinkage in solidifying lead is much higher than the shrinkage we normally think of when discussing how much a cavity should be oversize. Molten lead has a density of about 10.6 depending on the actual temperature (lower when hotter) whereas pure lead has a density of 11.4. This means the volume of the molten lead is some 5 to 7% larger than when in a solid state - and it also means we must somehow add some 5-7% extra lead to the mold during the few seconds it takes to fill the mold. This is not as dramatic as it may sound as the solidifying is a continuous process and the front of the boolit is already setting while the rest of the cavity is being filled. (that is why we have wrinkled boolits from a cold mold, as the lead solidifies instantly when it comes in contact with the cavity)

The moment the cavity is filled, we have a semi-solid "shell" surrounding a still molten core - this is where the sprue comes handy: when 44Man fills his mold from a ladle and keeps the spout onto the sprue plate after filling the cavity, the ladle acts as a non-freezing sprue and the cavity can draw lead from it right up until the boolit has fully solidified.

Unfortunately, when using a bottom-pour pot things are not quite as simple, even when "pressure casting" as the sprue seems to freeze before the cavity can draw the last drop (at least, that is my experience) Even if the base of the boolit looks fine, a closer look will often reveal a tiny hole indicating a cavity in the base. I found that keeping the spout 1/4" above the sprue plate and using larger sprue holes and countersinks makes things easier to work with, but to each his own...

Even with a large sprue and a large hole, cavities can form: When casting the slug to the right below I noticed the sprue didn't "dimple" when it was setting. When i opened the mold it revealed a large "sink hole" in both the sprue and the mold. The hole in the slug actually goes right through the slug and out the nose!

http://i1370.photobucket.com/albums/ag248/driftwood4/f6703a3e-c5c3-4bd5-82a4-5a122047382e_zpscb77eacc.jpg

[Bigslug]

I've become a real fan of the thick Hensley & Gibbs style sprue plates with a trough down the middle, as this channels the weight of the molten metal down towards the cavity - basically giving you something of a pressure cast. I also really like how this cuts down on spill over the sides of the blocks.

[Old Caster]

I feed the boolit with molten metal from the ladle. Keep the ladle in contact long enough and the boolit will need nothing from the sprue.
Now you bottom pour guys need more sprue.

If you pressure pour from the bottom, hardly any sprue is necessary because the mold can be held to the pot as long as you want and I will connect the last cavities sprue to the next by moving the mold backwards after pouring each cavity. That way I can pick up my entire sprue with a pliers and throw it back into the pot each time. I have to wait to open the mold anyway so I don't go too fast depending completely on how many cavities and how large a bullet. That way the sprue is still hot and it is taken care of immediately

[Old Caster]

It is important to realize that the shrinkage in solidifying lead is much higher than the shrinkage we normally think of when discussing how much a cavity should be oversize. Molten lead has a density of about 10.6 depending on the actual temperature (lower when hotter) whereas pure lead has a density of 11.4. This means the volume of the molten lead is some 5 to 7% larger than when in a solid state - and it also means we must somehow add some 5-7% extra lead to the mold during the few seconds it takes to fill the mold. This is not as dramatic as it may sound as the solidifying is a continuous process and the front of the boolit is already setting while the rest of the cavity is being filled. (that is why we have wrinkled boolits from a cold mold, as the lead solidifies instantly when it comes in contact with the cavity)

The moment the cavity is filled, we have a semi-solid "shell" surrounding a still molten core - this is where the sprue comes handy: when 44Man fills his mold from a ladle and keeps the spout onto the sprue plate after filling the cavity, the ladle acts as a non-freezing sprue and the cavity can draw lead from it right up until the boolit has fully solidified.

Unfortunately, when using a bottom-pour pot things are not quite as simple, even when "pressure casting" as the sprue seems to freeze before the cavity can draw the last drop (at least, that is my experience) Even if the base of the boolit looks fine, a closer look will often reveal a tiny hole indicating a cavity in the base. I found that keeping the spout 1/4" above the sprue plate and using larger sprue holes and countersinks makes things easier to work with, but to each his own...

Even with a large sprue and a large hole, cavities can form: When casting the slug to the right below I noticed the sprue didn't "dimple" when it was setting. When i opened the mold it revealed a large "sink hole" in both the sprue and the mold. The hole in the slug actually goes right through the slug and out the nose!

http://i1370.photobucket.com/albums/ag248/driftwood4/f6703a3e-c5c3-4bd5-82a4-5a122047382e_zpscb77eacc.jpg

If you get holes like this when pressure pouring it is because your pouring too fast. If you pull your lever without a mold under it, it should not be a solid stream all the way to the base but just almost. If something breaks loose from the pot, it will float to the top of the bullet base but not make it back into the sprue through the hole because it is turbulent and heavy. If it takes about 2 seconds to fill a 200 grain bullet the speed is about right.

This works great but it has its downfalls too. The flow will clog faster and easier if it is slow and either you are constantly changing the flow or you need another pot to keep the level about the same or at least within about 2 inches of the same level. Just adding lead to the pot to keep it the right level might lower the temperature enough to mess up your cadence.

Also some molds aren't quality enough to pressure pour because you will have fins or lead will get between the mold and plate to make a flat fin in the bottom of the bullet.

When using a ladle, and keeping contact with the mold it will pressure pour also but only has a column height of 1/2 to 1 inch depending on the size of the ladle but the constant feed of lead for as long as you want it can be achieved. With a ladle, you also don't have a buildup that can suddenly cause a pit like in your bullets above because the ladle is moved around enough that the hold stays cleaner.

If you just want a bullet that shoots and aren't worried about the absolute best you can make, just pour in the top and don't worry about it, but if you want the best of the best, you have to put more effort into the pour.

[44man]

Very good comments.
Seems the ladle holds heat better and with smaller boolits I pour both cavities without refilling the ladle. I use the tip method and as soon as the first sprue sets, I pour the second. I don't want a leak at the ladle nose.
Bottom pour nozzles don't seem to be as hot, no heating coils in the pot bottom. Main reason they can muck up fast.
I tried them too many times and even had the sprue freeze trying to pressure pour.
have to watch your pot too, some I tried had such a long cycle time that lead started to harden in the pot. Temps were all over the place. I went through three thermostats in an old Lyman, all failed.
I use a Lee 20# pot, have for years, just can't beat them for the money. I plugged the pour hole with a tapered brass plug and got rid of the hokey stuff on top so I have room for the ladle.
My friend has 2 RCBS pots and a Lyman. In his whole life, he has never cast a good boolit. His bench and garage floor is so full of lead spatters he needs a fireman's suit! :bigsmyl2:. I could shovel his floor and make a few hundred boolits!
I can't type except with one finger of each hand, need to see what letters I hit and some are worn so I keep hitting wrong ones. To see friends cast as I teach them, it is amazing how they can't use both hands. They turn the mold as they tip a ladle off, spill the sprue. Then I think of my typing!
How in the heck does anyone play a piano?????
The ladle should never be used to flux or stir, keep the nose out of the lead but it will still need wiped now and then. I also empty it and tap the back on my vice to make sure the hole stays open. I did drill out the hole a little.

[blikseme300]

I've become a real fan of the thick Hensley & Gibbs style sprue plates with a trough down the middle, as this channels the weight of the molten metal down towards the cavity - basically giving you something of a pressure cast. I also really like how this cuts down on spill over the sides of the blocks.

I have a number of H&G gang molds and pondered why they had the trough. This set me thinking about doing this to my Lee 6-cavity molds. I used a 3/8" ball end mill and milled a trough approx 1/8" deep. Cleaned up the sprue cavities using a 90* counter sink and deburred. Using my custom bottom pour pot which has a 2.5mm spout I can do a continuous pour which leaves a generous sprue and perfectly filled out bullets.

[44man]

I make my sprue plates from 1/4" stainless. Can't use a counter sink, need to lathe cut the tapers on a face plate. I leave end mill marks on the bottom and the top of the mold. Never polish those surfaces or try to lap them. They will never be flat. been there, tried that a thousand times, only cure is to mill again. Mill marks are the best to hold lube and vent.
I cut vent lines .002" deep on one block only, none needed on the other half.
Why stainless? Got it free of course. Lead has a hard time sticking to it.

[Old Caster]

If you like sprue plates with a groove and want it for a Lee 6 cavity, there is a group buy in effect for steel plates and cam levers.

[DrCaveman]

This thread has got me experimenting once again

Been doing the bottom pour thing for the past couple years since i bought the lee production pot iv

Pretty happy except i have been subject to the minimum temp requirements for the lee to actually POUR. Never ever below 700* does it pour. I get freezes mid session when i try to back it down. Its probably not as clean as it could be, but im not about to empty the pot every session and scrub out the unavoidable impurities. That seems silly, insomuch as that i must be using the wrong tool, rather than employing the wrong maintenance techniques

Tonite i tried ladle casting with the lee dipper. Looking good so far! I am waiting for the micrometer to tell me if i got rid of the base band shrinkage, after they cool enough to measure

A lyman ladle has made its way into my shopping cart. Measurement results will dictate whether i plug up that bottom pour hole or not

Thanks for the pics and stories regarding ladle pouring. I seem to observe that a lot of the most successful casters do it no other way

[leftiye]

MOLD TEMP!!! Don't let that boolit freeze quickly. Light frosting will probly happen, and be good. And yes, feed the boolit as it freezes - either from the sprue, or from a HOT ladle.