Model 100s do not have a stellar reputation for reliability.
There was/is a recall for firing pin problems. There are circumstances under which the original pin could wind up jammed out of the boltface, resulting in the rifle discharging when the bolt closes. When the rifle was modified, a mark was applied. Can't tell you what it is, though.
here you go
Cheers
If you have any questions concerning this notice, call Winchester Product Service 1-800-852-5734 or write to Winchester Firing Pin replacement Notice, PO Box 10 Cottage Hills Illinois 62018 Attention Product Service Dept.
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The difference in the old firing pin and the new one is as follows. The old replaced style, was totally lathe tuned (round). While the new recall style is similar in lathe turning on the front and back, but in the front midsection it has two flats milled, one on each side. This makes the center section stronger. Also replaced is the bolt sleeve lock pin (firing pin guide) which was made to accommodate this different shaped firing pin
Part number for the new parts are, firing pin =1391ND, bolt sleeve locking pin =1491ND
The word was at the time this recall was in process was that if the firing pin would break at the mid section and still remain in the gun as two pieces, the possibility of a premature discharge before the bolt was locked was possible. This apparently was caused by the firing pin tip (now not having a retracting spring) to be stuck forward, and thereby slam-firing upon chambering.
The responsibility for the recall apparently was on Olin, as they were the parent company at time of manufacture. Olin set up regional recall centers at three established US gunshops. There was a manufacturing delay in the replacement firing pins, and a backlog occurred, also some collectors did not like the idea of shipping their guns long distances. Olin then also authorized other gunshops to make the required alterations. Upon completion of the recall, the shops were to test fire the firearm and to stamp an assigned letter on the inside top of the receiver as seen thru the magazine well with the bolt retracted. The letter “B” represented Bolsa Gunsmithing, “L” was Lefever, and “N” was for Nu-line Guns. The letter “X” apparently was for all the other independent shops. However this identification information did not get communicated to some of the smaller shops at the start of the project. The only way to tell if the gun as been modified, if the ”letter” is not present, is to take the barrel & action out of the stock, remove the trigger guard assembly and the try to rotate the firing pin by twisting it. If it does NOT rotate, then the firing pin recall HAS been performed.
