Mine comes from a "friend". Years ago I was given some 30-30 win. reloads. Being older and assumed knowledgeable my trustworthy friend had to know what he was doing........ The rounds were hard to chamber in my 336C to the point that extra pressure was required to chamber the rounds (that would chamber) after firing 2 or 3 I noticed they were a little more umph than usual. About this time common sense took over and I put his reloads aside. Later on I asked him what the deal was with the ammo he said "I load them hot, that way usually the primers come out and saves a step". Later on I found out he also gave someone some 38's who was shooting to qualify for CC permit and they had 3 rounds jam in the BBL.
Lesson learned early about anothers reloads. Don't take anybodys nor do I load for others.
My personal error came from a recent round of 45ACP loads. Somewhere between old age and blindness I was off on seating depth had several rounds that would not chamber, my fault left them long. I usually setup and measure to start then spot check as I go. May not have had calipers properly zeroed to start is all I can come up with. As I would hate to think I short stroked a seating process.
My Favorite Toys: SIG 220, Kimber Ultra SPII, Colt Snubbie, Browning Hi-Power, Browning BLR, Mini 14, M1A1 & AR-10.