I am down to the last 300 of a box of Winchester small pistol primers, and am experiencing about 5% won't fire with the first drop of the hammer in my S&W model 13. Nothing in my reloading has changed, no oil anywhere near the RCBS universal priming tool I use, no moisture or extreme heat changes here at all.
I Have tried seating the primers with a firm seat, almost flattened, and then lightly seated, just under flush, no difference, still 5% fail.
Powder is Winchester 231. 4.9 grains under a 125 grain bullet.
These primers are about 10 years old.
Any Ideas?