Some of my colleagues are reporting a rash of broken bolt tails on Union Strongbolt (ironically) mortice deadlocks. This is something of a pain as we got these in in order to replace ERA Fortress mortice deadlocks. The Fortress was failing in so many ways it wasn’t viable to repair them at all; and Strongbolts, from the well-regarded Union brand, were very reasonably priced and were nearly an exact replacement fit. But now the bolt tails are breaking.
They aren’t alone in this, Legge and Assec suffered the same thing a year or two back. The obvious, and almost certainly true, reason for this is that nearly everything is being made in China, where most companies who’ve sent their manufacturing there have no idea how to go about climbing the vertiginous mountain that is getting Chinese factories to do any qualtity control. The bolt tails are probably being die-cast in cheap metal in a cheap process.
You should be all right as long as your mortice deadlock operates without strain. If, however, your door is warped or the lock was badly fitted, and the bolt is fouling the side of its keep as it’s unlocked, then the stress eventually fractures the bolt where the key-curtain mechanism picks up the bolt and withdraws it. A mortice key (the “Chubb”) should turn easily; an arthritic sixty-year-old (me) should be able to turn it using just fingers with no effort at all. If you feel you’re needing to use more force than this, try pulling the door towards you (or more rarely pushing the door away from you) before you turn the key to unlock. If it gets significantly easier then you have got an at-risk bolt and you should always carry out the door pull (or push) before you turn the key. (Turning to lock, rather than to unlock, isn’t as much of a problem, at least as far as breaking the bolt is concerned.)
Luckily, although I’ve bought a fair few of these into stock, I haven’t fitted them yet.