I have made an early medieval wooden crossbow (posted a while back on here), and am currently restoring a 'classic' rifle-stock sporting crossbow which is a complete individual creation of someone unknown, which I found in a market/emporium. It is an alloy prodded target weapon (nothing whatever to do with Wham-O Powermasters!) which I can tell has been very well designed and made, both from a mechanical and bow-design viewpoint. I have made a string for it and leather-backed the alloy prod for safety and generally cleaned it up etc., but when I test-shot it twice I had the same kind of misfire where the string goes under the bolt. This bow has a deep bolt groove for a 3 fletch bolt and I made a few test bolts from old field arrows by cutting off the nock basically and putting on a pile at the right length. I had this problem at first with my medieval bow also - though this has a shallow bolt groove and uses two-fletch bolts, and the problem seemed to disappear (apart from the odd one every now and again) in general adjustments etc.
I wonder does anyone know why this might be happening? Can the cock-feather of the bolt lift a bolt up if it even slightly compressed in the groove? It creates a terrible dry-fire which I want to avoid as it rips off the cock-feather of the bolt and risks the bow and the string , and there might be a simple solution I know nothing about . I say again I am new to crossbows - making, repairing, setting-up etc. and although I will be able to understand all the practicalities to their operation, I know next to nothing and am at the bottom of the learning curve! Any suggestions will be very happily received