Drilling a core mold?

[guywitha3006]

Maybe I am over thinking this but I have a blank Lee 6 cavity mold. I want to use it as a core mould for for 9mm. If I were to buy a new 5/16 bit and chuck it into my drill press quill it make a smooth enough cavity that the mold will easily drop the cast cores? Or is life not that simple?

[BT Sniper]

It is simple enough, and it is simple to screw up too

5/16" would possibly be a little big and drill bits tend to cut oversized holes, I would go one size smaller for the 9mm cores. It is always easier to make the hole bigger but..... it's a lot harder to make a hole smaller. Under or around .300 would be my choice for cores with the 9mm depending on what is used for a jacket.

You don't need a perfect tight fit for a slug of lead to be used for a core, smaller diameter cores will get squished just the same.

BT

[clodhopper]

You might want to look into buying a reamer, or more specifically a chucking reamer.
There are lots of online sources for such tools. Drills and cutters.com is one that I have used, and also there are big companies like Enco and MSC. (Their sale catalogs will make you drool with tool lust!)
If you use a reamer, drill the hole undersize.
Screw machine drills will be shorter than standard drills, so what ever wobble your drill press has, will be less magnified at the point of the drill.
I am giving some thought to making core molds and eager to see your results.

[Sasquatch-1]

I did this with a single cavity mold I didn't use anymore. The slug drops fine, which was your main question I think. This was done with an old bit.

I don't know how hard it will be to center the whole in a blank mold. I just squeezed the hole that was there around the bit.

[just bill]

I 've seen successful core molds done with drills, however when I talked to MSC they said parabolic drill bits were a good choice, but not as good as reamer. I bought a .25 one and converted a 6 cavity to an 11 cavity. Just be careful about chip build up.
Bill

[guywitha3006]

Hopefully I will get a chance this weekend to try and not hack it up. My thought is I will find a bit that just barely fits through the sprue plate and then make a pilot for each existing hole in the sprue. The idea of making an 11 cavity has crossed my mind, as I could go a little narrower and deeper. I plan to use cartridge brass jackets so I think I will be shooting for about a 65-75 grain core. worst case is I am out the the blank that has been sitting around for still in the box for the better part of the year.

How much narrower can you make the core in relation to the jacket without seeing any adverse affects?

[clodhopper]

If you mark your sprue plate with the drill it may take some polishing to get the sprue to come off the plate during casting.

The only problem with a core to small, is if the core is so long that it deforms out side the jacket during the core seat process.

Back to your original idea, if your drilling scratches the cavity, aluminum is pretty easy to polish smooth.

A reamer will give you a smoother and more cylindrical cavity than most drill bits will.

[guywitha3006]

Where would I get a reamer? I am still a basic tool guy at this point.

[country gent]

Another simple trick is to clamp a piece of paper in between the blocks when drilling this gives a small soft gap for drill point to follow. The reamer will give a much better finish and truer hole than just a drill possibly saving some force swaging bullets. Use lots of oil while cutting. Aluminum tends to gauld to cutters other wise and this ruins finish. Clear chips frequently and add oil regularly. Beeswax is also a good cutting lubricant for aluminum. Some waterless hand cleaners are good also.

[ncbearman]

All valid points. Cut 1 cavity then cast a core and see how it is. You could also use a cast core to Lee ment the cavity if need be. Like BT said you can always go bigger .....

[newcastter]

You don't need a freaking reamer to drill a core mold, I've done it 5 different times with my drill press and I think I used a 5/16 for my 9mm cores but not 100% on that, will double check. Any way the key is getting exact center for your start point. If it is off center a bit it will be harder to drop out as one side will have a little more holding on to the core. If drilled on center it will drop beautifully. Hope that helps.

[just bill]

There is a thread somewhere on this site showing a drill pressed core mold . I tried to find it but struck out. It was about 2 years ago.
Bill

[guywitha3006]

Well I order a couple of Stubby 1/4" bits if they get here this weekend I will give it a go. I think I will start with 6 cavities and everything goes well and the cast nice I will consider drilling out the other holes to make it an 11 cavity.

[ncbearman]

Do you need other core sizes? Just sayin. You could drill more than 1 size core in the same mold.

[BT Sniper]

1/4" is about max diameter for 11 cavities. Any larger and the space between the holes gets very small.

BT