Slinging takes time and energy. Why waste it?
I mean why waste it slinging stones that have aerodynamics similar to bricks Inspired by Mark Findlay's article Fifty-Second Bullets (http://www.slinging.org/41.html)I bought a 25 kg cement bag and started experimenting.
Handmade cement ball still has many imperfections, surface never is smooth enough and it takes time. The same time could be spent making cement glandes which are more advanced projectiles.
Using same amount of energy in throwing process you can achieve much more. Distance increases dramatically, since you have to use a bit different way in releasing glandes to make them fly point forward, the spin that is added to them makes them stable and much more aerodynamic in flight. You have noticed that when stone is released due to its imperfect relief it may act differently each time, and suddenly change its trajectory at any point, it wouldn’t happen with glandes. That’s why I suggest using your own made cement glandes. Every time you will use same shape and weight, you will learn much faster, and results will be more consistent and satisfying.
If you decided to buy cement bag keep in mind 25 kg is much heavier than you think This amount will be enough for a long time, so I suggest buying a bit more expensive (faster drying, smaller particles…) but simple and cheapest one can do the job as well.



I suggest you buying a special tool for mixing spoons and knifes are bad choice and gloves so that skin would not be damaged.
It is good idea to separate cement to smaller plastic bags.
First thing in making glandes is getting a shape. That was the most difficult part for me. There are not so many things similar to American football shape. Fortunately simple candle is available to everyone. First thing you need to know about wax – it expands while melting. If you decide to melt it in oven keep an eye on it.
I used small glass for melting my wax in. After melted wax stays a few hours in room temperature, it starts shrinking, in my case small sag appeared in the middle. Most difficult part in this process is finding hard enough object that could carve round shape in wax. I used nutcracker it has similar shape, have a good grip, and is hard enough. I would suggest keeping object steady and turn glass with wax. Shape becomes more round.



After you peeled out all unnecessary wax, make surface smoother with winger, and put some cooking or any other oil on the surface. From now on oil is you friend
Making glandes “half” is very important part of the process. Put enough water on cement to make it runny. Pour it into the form and use “vibration” so no bubbles would be left inside.  Leave it in dry and warm place, but don’t forget that wax melts, and radiator might be too hot. After about 4 hours I turn it upwards and it easily drops out. After having two identical you have a perfect beginning.
Base of the halves have to be polished in order to be glued together, that is important part in order to make it centered.
 


In this picture you can see that the base have to be polished. You should buy rasp, or in extra situation you can use one that girls use for nails Sand paper is very helpful in last phases of polishing prototype gland.

Putting together and fixing with glues will not be difficult. Leaving it to dry and waiting for it will
After you have one piece you can start polishing it. Keep in mind that the sharp points should be in one axis so the projectile would not waste energy trying to get straight.
 
Holding projectile to its end with fingertips and turning it around you can notice imperfections and fix them. Making projectile wet while working with it might help very much.
Finally leave it to dry before polishing it last time.



After final touches your prototype gland is ready to be painted in order to make future process easier.
Last few prototypes I managed to broke because I used only oil, and that is not enough when making prototype forms. Cement when it drys becomes very strong and it will be a problem when taking prototype projectile out of it. But in time you will hang on it.
I chose simple plastic cups for the base of the future forms; it’s cheap and easy to cut when you want extract dried cement.
You should not fill cement cup to the top, it is better to leave one centimeter of space, so in the future, when making cement glandes you would know where is exact center and how precisely these halves should be put together.



After putting wet cement to the plastic cup, cover gland in oil, gently rotate and use “vibration” to put it’s half.
Let cement dry or you can try to rotate prototype gland and take it out in order skip possible problems of removing it from dried cement later.
If you see that you cannot take prototype gland out, try to cut with knife some cement of from form, use water or other means. It is better to break cement form than lose your prototype gland.

After you made cement forms, you can polish inside to make it smoother. Use lots of oil so later wet cement would not stick to the surface. Each time I make a gland I put drop of oil to both forms, upper and lover. That helps a lot when extracting dried cement projectile.

Put some of wet cement mass in both forms, put them together and squeeze, use wet sponge to remove unnecessary cement.
What is really good about cement forms, you can put them in the oven if you are in the hurry, so you can increase speed of the whole process.



I hope you will at least consider this possibility since cement is not so expensive.

If you have 10 forms. 1 hour is enough to extract hard enough cement gland and put new one in. You spend an hour a day and on the weekend your hands will hurt from slinging

Good luck improving technique !!!

Thats the good thing about cement, it is cheap. It means if you already made forms for at least 5 glandes, you can spend 10 minutes oiling them mixing cement with water and putting full forms on radiator or in dry corner at home. Through the night is dries enough and you can remove them in 2 minutes to leave projectiles dry faster. And in your case when you have only 10 minutes, you can have so much more fun with 1 time glandes
I sling on the weekends, and it is quite frustrating looking for stones in same places, because after each time amount of suitable rocks decreases very fast. And its better to spend those 20 minutes at home throughout  all week making projectiles than during "slinging time" looking for stones
If I would be a "full time" slinger as people in ancient times, i could adapt to each stone and shape, but in these days who has ability to practice slinging for 20 years everyday since childhood ?

Before I used glandes and throwing technique and adding spin to projectile 100-150 meters were my average distance. Now 200 meters became common distance. Be careful glandes are faster, have more energy and are much more dangerous than round shaped projectiles. Since its 1 time projectiles slinging near water gives exact feeling of distance, and its more fun seeing where gland lands, try it

[quote author=curious_aardvark link=1196999458/0#3 date=1197030785]so do you use the cement forms to mould the glandes and then remove the wet shapes and leave them to dry outside of the moulds - or do you leave the glandes in the moulds to dry ?[/quote]
It takes about 1 hour (at least for my cement that I use) for the projectile to become strong enough to be removed, because it takes time for cement to get stiffer (if it is not, at the moment when you separate molds from each other projectile will brake to two parts). And when you remove the molded cement its strong enough not to change it's shape. If you heat up molds it might be faster. Of course  it depends what consistency of cement you put to the molds, runny cement leaves one of the ends misshapen.