Advice for MP hollow base molds

[vagrantviking]

With the sale on at MP I went ahead and bought a few very beautiful hollow base molds. Truly amazing to look at!

After a cleaning and several heat cycles in the oven I am finding it a challenge to get good results with the hollow base Webley mold. Using 20-1 alloy at 700-720° the hollows fill out nicely but wrinkles on the exterior. At 800° the outside looks pretty good but there's voids in the hollow base.
Similar issues with the shotgun slugs. Its not so bad with the 41LC maybe because of the thinner pins?

I've been preheating the mold to about 400° in a toaster oven and have a hotplate on the way to see if that works any better.

Anyone cracked the code for good results with these? They are pretty enough to put on the mantle but I really want to make some bullets that look just as good.

[BLAHUT]

I have lee hollow base molds; work great straight out of the box with pure lead.

[megasupermagnum]

I don't have that particular mold, but I've casted similar bullets with similar molds. Some molds are just pickier than others. I also find that no matter what you will always have a high rejection rate on hollow based molds, more so than hollow point molds. My guess is because hollow bases are usually quite a large plug, and there is no way to vent the entire thing. Even at my best, I often have around 10% rejection for hollow based bullets or slugs just on voids alone.

The best advice I can give is that the way you fill the mold makes a pretty big difference. When it comes to any large bullet, but especially hollow based bullets, I only ladle pour them. I want as rapid a fill as I can get. You can try pressure pouring with a ladle too, but I find it's usually better to just get the sprue plate temp right, and then normal pouring fast is best.

[NyFirefighter357]

If it's the brass mold you need more heat. That mold needs to be very hot, once you find the right temp., you need to work fast to keep it hot.

[Bigslug]

There is a break-in period with molds, and I usually find there's a settle-in period with each casting session. The perfect bullet from the first pour is damn near a unicorn.

The Webley bullets have thin lube groove bands, and the base pins are steel, which will hold onto heat less efficiently than the brass mold body. Both are a requirement for more heat, and such molds will require their own cadence. I would say that if you have good lube grooves but flaws in the base cavity, you're probably very close. The hotplate should help, & I wouldn't hesitate to take the pot up to 825F and only back down when it starts to behave. With 20-1, you should have plenty of tin, but there is no law against experimenting with more. In our stickied .38S&W Webley thread, it's mentioned that the Brits went as hard as 12-1 on the .455 before WWI, for reasons known only to them, and backed off to nearly pure lead due to wartime demand for the tin. Those would have been swaged bullets, but my point is that a higher tin content would not be outside the realm of authenticity.

Then there's the "keeping it real" aspect. If you have a good exterior and only a swirl of imperfection where the nose of the base pin lies, it's worth remembering that the MKII and MKIV bullets are short range, nose-heavy, 600fps meat cleavers that are not subjected to high-intensity anything. It's unlikely to make a difference in your shooting, and you can't see the base cavity when it's loaded in the case anyway.

[georgerkahn]

With the sale on at MP I went ahead and bought a few very beautiful hollow base molds. Truly amazing to look at!

After a cleaning and several heat cycles in the oven I am finding it a challenge to get good results with the hollow base Webley mold. Using 20-1 alloy at 700-720° the hollows fill out nicely but wrinkles on the exterior. At 800° the outside looks pretty good but there's voids in the hollow base.
Similar issues with the shotgun slugs. Its not so bad with the 41LC maybe because of the thinner pins?

I've been preheating the mold to about 400° in a toaster oven and have a hotplate on the way to see if that works any better.

Anyone cracked the code for good results with these? They are pretty enough to put on the mantle but I really want to make some bullets that look just as good.

Just as a suggestion -- no guarantees -- I had similar challenge maybe three years back -- also a MP hb mould -- and my "solution" was to dribble some of the "100% pure tin" I had previously purchased from RotoMetals in the mix -- this following OCD fluxing. Bion, for me, the added tin was the charm.
My experience...
geo

[vagrantviking]

I've heard that the trick is more heat and tried up to 800 but will have to try even a bit more. Never had to get nearly that high with anything before. Hopefully the hotplate will put more heat into the pins and make a difference.

Already cringing at the cost of 20-1 tin bit might have to experiment with more. Having trouble finding enough for my bpcr bullets as is.

Thanks for the reassurance that I'm not entirely off track with what I've been doing.

[gwpercle]

VagrantViking ... Is your mould brass ?

Gary

[vagrantviking]

VagrantViking ... Is your mould brass ?

Gary

Yes it's brass molds I'm struggling with.

I had a steel single cavity RCBS Webley mold that is considerably easier to use.

[Winger Ed.]

I'd run the heat up until you get a little bit of frosting, use a hot plate to set the mold on,
and be sure there is enough Tin to get a good flow without it running out into the vent lines.

[Bigslug]

Already cringing at the cost of 20-1 tin bit might have to experiment with more. Having trouble finding enough for my bpcr bullets as is.

It's certainly not necessary. The last time I ran Webley MKII slugs it was with rendered shotgun slugs that tested out as a low-antimony equivalent of 40-1. Probably with a few lumps of tin tossed in for fillout, but certainly nothing like 20-1.

[rintinglen]

Get the mold hot! Very Hot! Get the mold hot, so much that it takes 7-8 seconds for the sprue to freeze. Then cast as fast as you can and ignore the boolits until you have at least a dozen casts worth. Only then do you start looking at the boolits. Trying to inspect as you cast merely prolongs the agony.

I get my best results by slightly offsetting the sprue hole and letting the alloy swirl into the mold, with the mold no more than 1/4 inch from the spout.

2% tin is more than ample for adequate fill out. If you're using 20 to one, your wasting money.

[BP Dave]

What rintinglen said: my brass molds, in particular, seem to run best when they are hot. Raising the temp on the lead in the pot can help a little, but the key is transferring that heat to the mold and keeping it up, which is accomplished by keeping up a high production rate (or maybe by using a hot plate, which I have never tried).

[megasupermagnum]

To clarify what some are saying, there is mold temp, and there is sprue plate temp, and they are somewhat related, but not directly. You can have a cold mold, and a hot sprue plate which takes 10+ seconds for the sprue to harden. In my experience usually the opposite is true with a brass mold. Mold temp is mainly controlled with pot temp and casting cadence. Sprue plate temp is mainly controlled with sprue puddle size. It can be tricky to get the temp control right with brass molds which is my main issue with them. Steel and aluminum are generally superior mold materials for ease of use. You can cast good bullets with brass molds, it just takes a little different cadence and pour.

You are already pre-heating the mold which can help. I see you are in Canada, but I assume when you say 800 degrees you mean Fahrenheit. I'm sure you are getting cold weather like we are here, which can change things slightly. 800 F is rather warm for pot temp in the summer, but in the winter it's not uncommon for me to run up to 840 F for pure lead. 800 F should be hot enough, but it doesn't hurt to try 830 F. Beyond that it comes down to cadence and puddle size. It is a little trickier since you have a steel base pin in a brass mold. You might have to run your mold a little hotter than ideal to get that base pin to the right temp.

I still think the main issue you are having is likely to do with pour rate. You do need a fast pour rate with large and hollow based bullets which is best with a ladle. Your alloy is fine. 20-1 is the best casting alloy there is. One last thing I can think of is you want as short a distance between the nozzle and sprue plate as possible. I've seen where pouring 1/2" from the nozzle has caused issues, especially in the winter.

[GregLaROCHE]

Try increasing the flow rate when pouring. Otherwise, a bit more tin as others have said. Most of my molds work better after they have been used a bit.

[vagrantviking]

Thanks guys. That's a few more things to try and more food for thought.

[cwlongshot]

Get it hotter! Not lead mold. Ya just need to cook off the impregnated oils.

I recently was lent a 411 HBW mold. After heating on hot plate to very frosty, it calmed & was dropping beautiful bullets. Had same issues last week with a MP 452490 & so did buddy in Cali with SAME mold! A hot plate is your best friend with a HP mold!!!

https://youtu.be/fjbTg_lEauY

[vagrantviking]

Well I'm revisiting this stubborn mold again. Probably put 10 pots of lead through it now with no real change in how it behaves. 9 of 10 bullets have an ugly void inside the bottom of the hollow base.

I have a steel mold that works fine and now a brass 41LC hollow base and a different design brass Webley hollow base that both drop nice bullets with a preheat and 750F lead but this one is still driving me nuts. Air temperature is steady at 56F. I'm using a Lee 20lb bottom pour pot.
I was going to try swapping the base pins but they are different lengths.

Right now the pot is on the way to 850F and the mold is preheating to a hotplate setting higher than I've used before. At 800F the bullets were sticking in the mold more than usual but still not frosting. We'll see what this does...

[Dusty Bannister]

High tin content and high temperature, might be careful you do not solder the mold blocks together. I really prefer the Lee 10 pound bottom pour pot because of the tapered nozzle and you can see what you are doing. The 20 pound pots I have, seem to have a flat nozzle and that might bleed off pressure. If the sprue plate is too tight, that might prevent proper venting. The pins do need to be hot or the alloy will cool too soon. Is the void an air pocket or shrinkage void?

If you have a casting ladle, I would give that a try, just to be sure you are getting a good rapid fill directly into the mold. It may be a little slower, but at the production rate you seem to have, it might be a lot faster as well.

[vagrantviking]

I've tried ladel pouring but it's been a long time and I have trouble getting in a rhythm. In some ways the Lee 10lb is nicer because it's easier to see what you are doing but they drip more and I like the capacity. Kind of wish there was a well designed 50lb bottom pour pot on the market.

It looks more like a shrinkage void. It's at the point of the hollow base pin and irregularly shaped.

This afternoons attempt started with the mold hotter than the melting point of the alloy but when the fist couple pours solidified they were good. After the mold cooled a bit the problem continued.

Might have to experiment more with a cooler lead temp. The bases fill out better but the deep, sharp lube grooves don't fill out as well.