Have you been able to make the molds?  I imagine it would be hard to get it perfect.  Are there any prefabricated "football" molds for concrete?

Chris

Cement actually _doesn't_ need to get rid of water to set up! It doesn't dry, but undergoes hydrolysis, a chemical reaction where the water is "absorbed" in the creation of the calcium hydroxide and silcate hydrates. A "good mix" is one in which there is enough water to fully convert the cement - too dry and the concrete doesn't flow/sets poorly, too much and you get a weaker set. Typically, the longer concrete stays wet, the better the end strength, one of the reasons that you wrap/sprinkle slabs to prevent premature drying. Concrete also releases a huge amount of heat as it cures - I vaguely remember someone saying that the Hoover dam would have taken more than a century to "dry" if cooling pipes and careful modular pouring hadn't been engineered into the construction process!

Back to glandes... The initial set should give you enough strength to demold the ammo after an hour or so. If you _want_ strong (rocklike) results, it may be beneficial to wrap the batch in wet burlap or plastic bags and let them cure for up to a week.

I think probably the easiest way to make sure that you get a good casting would be to shake the mix into the cavities. If the sprue has enough volume so that the cement can settle, you should get nice voidless little ellipsoids. Setting the mold on a soft surface (old tire/pile of rags/peice of foam,coil springs) and beating on it for a minute or two with a mallet should do it!

And hey! the flat spot might even help aerodynamics. Thrown point first, the sharp edge should help promote clean separation of the wake. As long as you can throw point first, a flat spot up to 60% of the minor diameter should be ok!

*Really* looking forward to seeing these guys!

Matthias

No specific recommendations . I'd suggest trolling the web for recipes that people use in "art-cast" concrete. You probably want to stick to a sand mix. Plasticizers are available to get a more soupy texture with less water. Using bagged premix it is usually on the label.

It sounds like your last batch was way too wet. How far away from the bag directions did you have to go to get it pourable? I was thinking about making a little resevoir in my sprue and then trying to "pack" the mix in using a rod. Might help drive out the bubbles as well. A bag of off-the-shelf mortar or uncoloured grout should be soft enough. I'd suggest thinset as a cheap bagged alternative too but I'm not sure if it might be too sticky to easily demold from a wooden form.

Matthias

Fellow Slingsters, ...I've posted some pics of this project as it has developed to date.

I got a 1.5" spade-type wood bit and simply ground it to a half-elliptical shape, then used it to bore 1.5"dia x 1"deep recesses in common 2x4 wood. 

I then sawed a section off the 2x4s to create openings into the recesses.  These recesses were smoothed a little (very little) with rough sandpaper, then coated with hot parafin wax.  The wood was heated in the oven, as well, to let the wax penetrate before hardening.

Before use, the mold halves were sprayed with cooking oil ("Pam") to let the cement come out.  They are held together with long bolts.

The cement used was quick-setting "mailbox post" mix.  It contains no gravel.  A slightly over-wet mix was spooned/shaken into the mold, then allowed to set up overnight. 

Result is fat ellipsoid cement glandes measuring 2" x 1.5" and weighing about 66grams.  I'd hoped they'd be heavier, and they might be with a different cement mix.

All work was done with hand tools, so a couple of the mold halves didnt match up perfectly.  Much better work could be done with a drill press, etc.

See pix: 
www.slinging.org/images/TEMP0003.jpg
www.slinging.org/images/TEMP0005.jpg
www.slinging.org/images/TEMP0004.jpg

mgreenfield

the quick rock is 20 buck for a 10 gallon bucket, that will make you aninsane amount of glands, and it dries so smooth they can be spray painted with one coat
it probably sounds like i work for the company but no i just think this stuff is so perfect...

Matthias, ....I put the fill holes on the side of the shape instead of the end because I thought I could get a bigger fill hole with less deformation of the overall shape.  Also, it meant I had to cut through less wood to make the fill holes.

The surface is pretty gritty/sandy, so will probably be tough on release cords and pockets.

They're plenty tough enough to NOT fall apart in the sling, but I think they'd split or fragment upon impact with a hard surface.

mgreenfield

those mortar balls didn't work out that great... i might have put too much sand in, but i think the mortar would have been too soft anyway.  when i used a full power whip, the mortar broke apart right out of the pouch; the last one left me in a cloud of sand, when i wasn't throwing it soft enough to launch it in one piece, but wasn't throwing hard enough to get the particles a good distance away.
i did manage to get a couple out without breaking, and they went maybe 80-100 yds with a nice easy lob? maybe it was for the best, if i had launched them at full power i probably would have hit a house on the other side of the field.

so now all i have to do is wait for the concrete ones to dry! should it really take a full week to cure?