cocked condition and the firing chamber is blocked so that a round of ammunition cannot be chambered preferably blind aperture 27 is located on bolt 6 so that bolt 6 need be drawn rearward only a short way to align blind aperture 27 with receiver aperture 25 to unlock the firearm bolt 6 may be held in place by cocking lever 35 while tumbler 19 is turned to the unlocked position of fig6 using key 21 spring 29 will then force cylinder lock 11 to retract within sleeve 10 thus moving lock cam 23 out of engagement with bolt 6 and receiver 3 bolt 6 will then be released for movement within receiver as a safety precaution tumbler 19 should be rotated to the locked position and key 21 removed following unlocking of the weapon in this manner lock cam 23 will be positioned as shown in fig7 and it will not be possible to inadvertently re engage lock cam 23 with bolt 6 while the weapon is being fired in the second embodiment of the present invention illustrated in fig1 21 the parts assembly and general operation of the locking assembly are substantially identical to those of the first embodiment with the exception that the locking action of the second embodiment is achieved through rotation of the lock tumbler only in the second embodiment cylinder lock 11 is not required to move vertically within lock sleeve 10 however lock shell 18 is prevented from rotating relative to lock sleeve 10 by the same cooperation of blind slot 14 and tab 20 as in the first embodiment fig1 and 15 illustrate the second embodiment in a semi automatic rifle 1 as before and in the unlocked.