Designing a bullet? Making a cherry?

[jcadwell]

What factors are considered when designing a bullet in terms of positioning lube grooves, taper of a gas check, normal oversize for a given diameter.... Say I wanted to cast bullets for a 223. The normal cast size is 225. Do I make a mold exactly 225? Probably not. 227, 230?

Also, how are cherrys made for cutting molds. I assume you start with an end mill, and grind it to the mold shape you want, and then sharpen it? Or is a reaming cutter used that has been profile ground.

I have a CNC mill and lathe at my disposal, and am interested in making a few molds for fun to work with the Lee handles and sprue plates I already have.

Any thoughts, ideas, or common processes would be most appreciated.

Thanks.

[Buckshot]

.................Pure lead shrinks the most, and the more highly alloyed it is with antimony the less it will shrink. Of course some tin also will have an effect on lack of shrinkage but antimony is the main ingredient having the most effect. In the Lyman manual they have shrinkage percentages for some alloys. I'm at work so I can't check.

Shrinkage is by percentages so the larger the slug in diameter the more the shrinkage. A 22 cal slug will shrink away from the cavity wall (we'll say) .001". A 45 cal slug shrinks .003" (again just an example).

A boolit cherry is tough to do and it has a hard job as it's cutting over it's entire surface as the blocks close on it, unlike a simple reamer which cuts only on the beveled leading edge. It's also tough in a round nose design as the flutes are all coming together around the ogive.

I think most reamers for a RN slug will lose a couple flutes when turning the ogive. For example you have have 5 flutes along the body but only 3 or maybe only 2 at the nose as the other 2-3 fade past the turn of the ogive. Unless you have some pretty sofisticated grinding equipment, getting the nose flutes just right and cutting even with each other is a major deal.

Easiest way with common equipment is to turn the shape of the boolit desired (allowing for shrinkage) in suitable heat treatable steel. You have the lube grooves turned in, GC shank etc. Then it goes into a 5C spinner or spacer to have the flutes cut. As you can visualize it clamped to the bed of a milling machine, the flutes will be cut straight. What to do about the curve of the ogive?

Without that fancy grinding equipment you're petty much down to a Dremel or Dumore and the MkI ModI eyeball and some magnification. And rather then trying to carry all 5-6 flutes around the ogive into a nose of rapidly diminishing diameter you allow some to fade, and carry 2-3 to the tip. The other benefit to having fewer flutes at the nose is that chip relief is greater. The negative is that the load on the remaing flutes is higher.

Naturally you want to have the majority of the metal removed before you begin to cut the cavity.

A lathe and mill with CNC capability is of no real use unless you plan on making a bunch of something, otherwise you'll be running them manualy. Of course you can write the code for the lathe to make one cherry blank if you want to. If you are going to cherry cut the mould blocks the lathe will be used for making that, and that's it. The mill will spin the cherry.

You'll need a double acting vise for the milling machine. You'll have one block half set up on each jaw and the cherry spinning between them. You then close the blocks around the cherry, opening them maybe a couple times to flush swarf out and keep the cherry cool.

If you were to lathe bore the cavity you'd need a faceplate and a means to fixture the blocks to it so the parting line is parallel and the faces perpendicular to the spindle axis when indicated in.

http://www.fototime.com/EC6E32186093ED1/standard.jpg

The above is just one way. A precision grinding vise mounted on a faceplate. The vise itself is parallel and perpendicular in 2 axis to .0002". Assuming precision mould blocks, the setup is repeatable for removing and replacing the blocks without re-indicating. Using the lathe you then use either a form tool or a set called spoons to do the cutting.

If you're going to do a short fat boolit like a pistol slug you can make a form tool. Basicly the turned design you want the slug to look like. Then you mill it in half and grind in the relief and stone the one cutting edge. You bore the minor diameter in the blocks just short of full depth and then feed the tool in to depth with the carriage or compound, and use the crossfeed or compound to cut out to the desired OD in one pass.

For a longer or more complicated design you might have one tool to cut the drive bands, and another you feed in to cut the form of the nose. Some tools can then be used for may similar designs. Lee lathe bores their moulds and if you look especially at their 30 cal designs you can see the similarities.

http://www.fototime.com/B14C8C7293C3501/standard.jpg

This is a Lyman 12 ga slug mould which has had drive bands cut into it with a tool in the lathe.

There are a couple members of this board who utilize both methods. One member has one of the small 7x12" lathes. Using home brewed tools has cut himself a very creditable set of 3 cavity blocks for a 100gr TC nose, plain based .314" boolit that shoots very well. He used a form tool for it.

Another member cherry cuts his own blocks using a nice double acting vise he made himself.

.................Buckshot

[Bass Ackward]

What factors are considered when designing a bullet in terms of positioning lube grooves, taper of a gas check, normal oversize for a given diameter.... Say I wanted to cast bullets for a 223. The normal cast size is 225. Do I make a mold exactly 225? Probably not. 227, 230?



Mr Caldwell,

Boy Buckshot laid it out for ya. But don't get caught up in the process until you know what you need. There are a lot of variables in the casting process that will affect diameter from the material of the mold which really affects temperature to the type of mix you want to use. Molding 22s requires a consistent temperature for consistent weight. Remember, you can only size the outside perimeter, so a slow to heat and slow to cool material should deliver the best results. For me that is iron/steel.

Richard already told you about shrinkage so you can look that up. My advice is to cut a maximum diameter to compensate for this. You can always size down as long as you are able to cut deep enough grease grooves which .... is going to be your bear. But if you size with lube in the grooves, this is often not a problem.

If you want a good HV bullet design or options for that, I would avoid the taper on the GC myself. Since this is the steering wheel of the bullet, I prefer the maximum contact of a straight shank. But again, in a little / light bullet like this, it isn't as critical as when you want to step on a larger one.

Then there is the saga of the .223. Many manufacturers cut large and sometimes long chambers to cut presure in case someone grabbed a military 55 grain round at the time by mistake. Make sure you slug to see what you need. I can actually chamber a .228 in one of mine. Now there are many ways to shoot cast of which you may know. The method offering the most successful (accuracy) options at lower velocity is filling that throat. At higher velocities I prefer closer to bore diameter myself. So logically, you can again see that going large gives you options.

You can buy some thread stock to make nose through sizers any where you need to obtain the desired diameter at a chosen hardness. Just remember that sizing a soft bullet will give you a diameter closer to your hole size and it will be larger if it is harder. But this effect is minimized in 22 caliber compared to others. Thread stock is cheap to practice on. :grin:

Have fun. Just let me warn you to hold down on the bragging after you get crankin lest you be inundated by mold requests. Just look at the responces on thread for 22 molds under the "Group Buy" molds section.

By the way, how much would you charge? :grin:

[44man]

A wonderful bunch of replys. I still use too much trial and error trying to figure out how large to cut a cherry for different calibers. When Lyman makes a mould, they base it on no. 2 alloy if I am not mistaken. Then if you use some other alloy the boolit will be a different size, pain in the butt sometimes.
The custom mould makers will ask what alloy you will use and can cut a mould for that alloy. I figure that they have a chart for each alloy for each diameter boolit.
Boy, would I love to have a chart!
It would be wonderful to write a book for us home mould makers showing all the different ways to cut them, but the chart must be super secret and without it, we are still in the same boat.

[Bass Ackward]

Boy, would I love to have a chart!

It ain't perfect, but the chart on pages 12 and 13 of the RCBS Cast Bullet Manual should get you started once you have a base knowedge to work from. IT only covers lino and 1-10, but since you have made a few molds already, you should be able to translate this and fill in the holes I would think. Better than nothin.

[44man]

Looks like I have to buy another book. Thanks.

[StarMetal]

Buckshot was talking about me as one of the members making a form tool and cutting cavities. I spoke with Rick recently and told him I was going to go from a dial indicator on my crossfeed table to a dial bore gage to cut my cavities the dimension I want. Well I did that today and hot ziggetty damn it works a whole lot better. I also installed a depth stop device on my lathe too so the form tool is in the same position for each cavity depth wise. Shucks, my cavities are starting to rival Lee's moulds. I just cut another three cavity 30 cal pistol bullet. I think next I may fool with cutting a TC nose 45-70 bullet. After that I dunno.

Joe

[44man]

Hey Joe, E mail me some pictures.

[Buckshot]

Hey Joe, E mail me some pictures.

Heck, put the photos up here so we can all see them.

..............Buckshot

[44man]

Good idea

[Bucks Owin]

Good idea

Sure is!

This is REAL interesting....

Dennis

[Brucifer]

That's it this thread just STOPS!!! whats up with that.

[swheeler]

That's it this thread just STOPS!!! whats up with that.

I've waited seven years to see the pictures of those molds and form tools;( guess it wasn't meant to be.

[theperfessor]

Don't know if this is of interest.

http://www.castpics.net/subsite2/HowTo/MakingBulletMolds.pdf

[HNSB]

Is no one making form cutters and using interpolation on a CNC mill?
That would be faster (for a multi-cavity mold), and allow for very small adjustments in cavity diameter.

[country gent]

I ran a cnc edm plunger for awhile at work and thought it would be ideal for making bullet molds. Cut a carbon electrode undersize rougher and finish, plunge to depth flat circle to size and next cavity. Only time you would need to be there would be to change electrodes. Rough each cavity on location then finish. If you could make the electrode this machine could "burn" it in hardness didnt matter. Grease grooves wouldnt be an issue radious could be easily formed anywhere you wanted, Angles the same. Since there is no cutting pressure no tool spring to worry about.

[swheeler]

thanks perfessor

[MtGun44]

With CNC mill, you can make a simple profile cutter and then drive it in a half circle,
easy to make any boolit diam you want, as long as it is larger than the profile
cutter.

I believe that MP makes mold halves, not molds, and then presses female alignment
sockets into one side and male alignment pins in the other. Using a fixed stop
for your mold half blanks should make this work pretty well.

Bill

[Brucifer]

Thanks Professor,
I think my garage is not big enough to add a surface grinder. Need to expand.