Imperfect bases

[John Hill]

I am casting .38 special SWC in a two cavity Lee mold and get many perfect bullets in a row but maybe 1/4th come out with the bottom of the bullet slightly "dovetailed" or rounded over instead of flat. It occurs when the mold is in pretty fast production and then the next cast will be perfect. I am casting ingots of mixed WW. What would be the possible cause of this?
Thanks
John

[AlaskanGuy]

How much tin are you using in your alloy?

[paul h]

I had that happen the other day when casting some 105 gr swc's from a lee 6 cavity mold which was plenty hot, though I didn't have nearly that many rejects.

I'm using a bottom poor furnace and it seemed to happen when I'd fill one cavity and the stream would spill over into the next cavity vs. getting a direct shot of alloy into the cavity. I'd try getting a straight shot of alloy into the sprue hole and see if that fixes the issue. Typically with ww's if there is any fillout issue, just turn up the heat. But in this case for me it was needing to get a clean shot of alloy into the sprue hole that fixed it.

[John Hill]

I am not adding any tin.
John

[williamwaco]

It is most likely caused by insufficient sprue puddle.

As the bullet solidifies, it shrinks and if possible pulls in more metal from the sprue.
The sprue puddle should fill the pour hole and spread out at least to the size of a nickle over the top of the sprue plate.

It should be hot enough to take at least three seconds to solidify.
Neither heat nor tin is causing your problem or they would all be bad.

Those bullets are OK to shoot but should be sorted to your plinker pile, they will increase group sizes over your bullets with square perfect bases.

[Prospector Howard]

Exactly what Williamwaco says. You have to have a good puddle there so it fills out as it solidifies. It's easy to test. Just pour one cavity with a tiny amount of puddle and the other with a good amount and see the difference.

[762 shooter]

+1 on puddle comments.

762

[Jim Flinchbaugh]

My limited experience has taught me that poor bases are almost always, a sprue plate temp issue.

[ShooterAZ]

I sometimes have that problem when my bottom pour pot is getting lower on alloy, turning up the flow rate usually fixes it. The pot pressure lowers as the alloy empties out. Sometimes tilting the mold a little helps too. As mentioned previously, make sure you get a decent sprue puddle. Also casting at 725-750 degrees gives me the best fillout.

[detox]

Lee sprue plate screw will loosen very easily causing inconsistant bases. A sprue plate that is too tight will cause rounded bases. A sprue plate that swings more freely will vent better and make a more square base when using bottom pour. Insted of using the single screw, I would use a single stud with two bolts locked together on top of plate to prevent loosening.

Mould halves that do not align will cause screwed up bases also. Current Lee moulds are famous for this misalignment. Receeding alignment pins. OOOOOOOOOOOOOOOOOOOOO!

[John Hill]

Thanks for the great info. I cast a couple of hundred rounds this afternoon (raining out) and had much better results with 700 degree plus, higher flow rate and bigger sprue plate puddle. Y'all are great!
Thanks
John

[detox]

BTW.......buy a good mould such as the RCBS 158 Cowboy

[williamwaco]

If you are interested enough to experiment, Try pouring smaller and smaller sprues.

When the sprue gets down to the size of a pea, you can actually see it being pulled into the mold.
A little smaller and you can see it shrink down into the sprue plate and actually leave a void in the base of the bullet.

[Foto Joe]

One of the things that you will find is that a smaller boolit like a 158gr SWC will take considerably longer to heat up a mold than say a 230gr LRN. Also since it's a smaller boolit with less heat to dissipate into the mold your casting speed will also be different than with bigger boolits.

I also cast 158gr LRN for 38 Special using a Lee 2-cav mold. Yesterday I had it heated up and running casting with COWW's too. My normal casting temp for that size is 650-675 max but at that temp it takes forever to heat up the mold to operating temp. "My" cure is to get the pot up to around 725-750 when I when I start. I cut the sprues off into an old pie tin and also drop the first 10-15 pours into the same pan. Once I'm up and running production I can use the cold sprues and boolits to cool off the melt to my preferred temp of 650-675.

Although I'm no expert by any means, I think that you'll find that each mold you have will tend to have it's own personality when it comes to temperatures and what works.

[HeavyMetal]

Plus one on the sprue plate temp issue!

Puddle is important to be sure but if the plate lets it cool to soon puddle size don't matter.

Try dipping the sprue plate every third cast, the area you would strike with a mallet or stick is just fine, and then pour.

I figured this out casting Lyman style HP's a few years ago were keeping both the pin and the plate hot was important in a huge way.

[Jim Flinchbaugh]

I think that you'll find that each mold you have will tend to have it's own personality when it comes to temperatures and what works.

This is NO joke, and I have to keep a notebook 'cause I CRS!

[Ben]

John Hill

A possible answer to your poor base fill out is a trick that I use on most all of my molds.

Pics illustrate my technique.

Catch is , you can over-do this and end up with " whiskers " on the base of your bullets. Go slow, it can pay VERY GOOD dividends if done properly.

http://img.photobucket.com/albums/v494/haysb/Lyman%20Mold%20Tune%20UP/020.jpg


http://img.photobucket.com/albums/v494/haysb/Lyman%20Mold%20Tune%20UP/023.jpg

Notice the tops of the blocks, you can see where I've taken a fine cut Swiss jewler's file and removed a small amount of metal. GO SLOW WITH THIS TECHNIQUE. ONCE METAL IS REMOVED, IT CANNOT BE REPLACED.
http://img.photobucket.com/albums/v494/haysb/Lyman%20Mold%20Tune%20UP/025.jpg

[williamwaco]

BEN -

Great photos.

Thanks

[Ben]

BEN -

Great photos.

Thanks

williamwaco

Thanks.........I guess I'm not the sharpest knife in the drawer, if I can see it , it helps me understand it.

Seems that there may be others out there like me. Sometimes good photos help to communicate things.

You can tell me about things all you want, but if you want to make some real progress with me .....let me see it or even better , let me do it.

Ben

[Spruce]

Great photos as always Ben. I like your way of communication as well. Great advice.

[C. Latch]

Something I have found is that once the mold is full of lead, a very gentle tap - like taping the handle bolt onto the wooden rail on my deck - seems to help metal settle into the mold and give me better fillout with my lee 358-158-tl.

??

[Le Loup Solitaire]

It has always been recommended to allow for a generous sprue puddle in order to feed any shrinkage and avoid "voids" or cavities that would otherwise form in the base of the bullet being cast. Sometimes they (the voids) are not visible and are off center which makes for inaccurate shooting. A second practice has been to allow the mold with the sprue puddle still liquid, to drop/fall about an inch onto a wood or lead block surface to "jolt" the blocks a bit....this is to encourage a more complete fill-out of the cavity. These tricks or practices sometimes require a bit of practice to avoid overly sloppy sprues and spattering, but they quickly become second nature. LLS

[garymcgehee52]

Listen to Ben, he knows what he is talking about. I do the same thing on my molds, just do it sparingly.

[Ben]

sparingly, sparingly, sparingly..................

[btroj]

Ben, I just did that trick on a a New mould from HM2 for my 9 mm.

I grew tired of lots of slightly rounded bases. It took 3 filing sessions. File a bit, cast a pot, repeat. I get a few with a tiny shocker on occasion but the cull rate dropped like a rock.

Sometimes ya gotta do what ya gotta do

[John Hill]

Ben,
I am assuming that you are only relieving the straight line where the two blocks meet as I detect a "bright" line in your third picture horizontally across the top edge of the mold. Correct?
Thanks
John
John Hill

A possible answer to your poor base fill out is a trick that I use on most all of my molds.

Pics illustrate my technique.

Catch is , you can over-do this and end up with " whiskers " on the base of your bullets. Go slow, it can pay VERY GOOD dividends if done properly.

http://img.photobucket.com/albums/v494/haysb/Lyman%20Mold%20Tune%20UP/020.jpg


http://img.photobucket.com/albums/v494/haysb/Lyman%20Mold%20Tune%20UP/023.jpg

Notice the tops of the blocks, you can see where I've taken a fine cut Swiss jewler's file and removed a small amount of metal. GO SLOW WITH THIS TECHNIQUE. ONCE METAL IS REMOVED, IT CANNOT BE REPLACED.
http://img.photobucket.com/albums/v494/haysb/Lyman%20Mold%20Tune%20UP/025.jpg