SSW001 Ammo.indd 52 20/07/2018 15:15 S S 1 5 : 1 5 SS 15:15 EQUIPMENT 052 SlingshotWorld 052 SlingshotWorld from Steel to Stone. A ccording to the Book of Samuel (1, chap 17) David “Took his staff in his hand, chose five smooth stones from the stream, put them in the pouch of his shepherd’s bag and, with his sling in his hand, approached the Philistine…” Then later it says, “Reaching into his bag and taking out a stone, he slung it and struck the Philistine on the forehead. The stone sank into his forehead, and he fell facedown on the ground.” At that point, Goliath of Gath was pretty well smote and we learned that water-rounded pebbles were best for slings. In our ‘old days’, the very idea of using steel balls as disposable ammo for a catapult was absurd. We all knew the best places to find the perfect oval flint pebbles of just the right size. I recall reaching into my mooching bag and feeling for the best one when spotting that pheasant in the woods. Chaquers we called ‘em and seeking them was an unending pursuit. But now, the cost of steel balls has dropped as part of the Chinese manufacturing boom and Bearing Warehouse and Fullmarks can both supply by the multiples of thousands in many sizes, often at lower cost than airgun pellets. I can tell you that several container loads of 9.5mm steels are sold each year in the UK trade. In China and on the continent, they target shoot with 8mm balls, so our UK team have bought some to practise with. Then there is lead. Any good at sums? A ball of lead is way more dense than steel, so an 8mm lead ball weighs the same as a 9.5mm steel one. To work out foot-pounds, you do the following sum.(Joules have less flavour for me, like measuring a motorbike in kW rather than horsepower.) You need the weight of your projectile in Grains. You need the chronometer speed measurement in Feet Per Second that your ammo went through at. Then, you multiply the speed by itself, then multiply by the Grain weight and finally divide by a constant - 450.24, to get foot-pounds. V2(ft/sec) x Weight in Grains 450.24 The limit to power in catapults is the acceleration due to elastic retraction and how long it was able to be acted upon. Thus a long, ‘full butterfly’ draw with both arms outstretched and longer bands, will make most power with a weightier projectile. Lead balls will be slower overall and have way less flat trajectories compared to steel but will carry more energy down range so serious hunters use them. Ammunition SSW001 Ammo.indd 52 20/07/2018 15:15