A good sling will get you vastly more range, especially in your case where you have a size limit (with a sling you can get more range, even with a shorter arm). A sling is somewhat like making your arm longer without adding much weight, except at the end of the throw (which is all that matters) the sling is rotating faster than the arm, and also sucking the kinetic energy out of the arm to the projectile as long as the sling hasn't passed the arm in rotation. A good sling will yield several times the range if well tuned.
Slings can be very accurate. Trebuchets used to hit castle walls consistently from hundreds of yards away with slings, and onagers are no different (I beat several trebuchets in an accuracy competition with one of my onagers). Onagers can be pretty inaccurate if you aren't careful though. Its good to make sure the sling is releasing before the arm hits the stop, or you can get inconsistent releases, and be sure that you either re-aim very well every shot or weight it down really well because onagers tend to jump around a lot when throwing. I should note that is you don't get everything right, you can end up with an inconsistent sling, I've heard of it, and seen people have issues with it, but I personally have never had the issue, and you can copy my sling design :)
Be very careful when tensioning your onager up to its breaking point, they can hurt you. As long as you arn't in the plane of rotation of the arm, and have safety glasses, you will generally be quite safe, but it varies on the design. Onagers if they break the arm, it usually goes in the plane of rotation (I'm thrown chucks of the arm backwards, but I have heard of them going forwards as well). If the rope breaks, its generally not exciting at all, my little onager has had a broken strand it its bundle for years. I've broken ropes in every single one of my onagers. If the frame breaks, it will usually just cave in a bit (then there is no more load on it), I've never had that happen though.
Marie (guest) 18 May 2011 01:12