Check for safety-off fire
Sorry Aurelius - I can't find it mayself, so here are the instructions for making that vital "safety-off fire" check.
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Safety-off fire
Correct safety action:
Cock the rifle and set the safety to “ON”.
You feel the resistance from the lifting of the cocking piece as it is held by the safety. Press the trigger. It should have very little resistance. But it must have some resistance - from the trigger return spring. The rifle must not fire. Now let go of the trigger, and set the safety to “OFF”. Nothing should happen. You will merely see or feel the cocking piece move forwards until it is held by the sear once more. The safety is functioning as intended.
Incorrect safety action:
Re-cock the rifle and set the safety to “ON”.
If you do not feel that resistance from the lifting of the cocking piece as it is held by the safety, then the safety is not holding the cocking piece and you are forewarned as to what will happen next: Press the trigger. You find you have to apply full trigger pressure. There is a (maybe tiny) movement as the cocking piece slips past the sear and the trigger goes slack. Although not very obvious, the cocking piece is now being held by the safety, but the engagement ledge is now beyond the sear! Now set the safety to “OFF”. As the cocking piece was already past the sear, the bolt will slam forwards as soon as the safety is released, and fire the rifle. This is a dangerous condition known as “safety-off fire”. The same can happen if the sear lost engagement because of a broken or missing trigger spring.
It may be caused by severe wear – or by Bubba trying to correct a non-working safety. You may say, quite correctly, that you do not need the safety function in practice, as for target shooting it is forbidden to have the rifle loaded and cocked except when you are on the firing point and about to take a shot. And anyway, some types of service rifle do not have a safety to start off with. That is true, but for us, the important thing about the safety-off fire and impact fire conditions is that they are a “sure-fire” indication that the trigger and/or cocking piece have been Bubba-ed. Or, of course, the parts are so worn as to be useless.
I strongly advise against buying a rifle with an impact fire or safety-off fire condition, as correction of this fault will require replacement of the defective parts, and will quite possibly make the entire project uneconomic
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Hope this helps!
Patrick