My first experience with slip on gas checks was with excess lube on the pin as it can often pull the check off. Examining the die I could see no way that there was a crimping shoulder in the die. The checks were brass. Sierra checks were slip on too but were of copper and there was no way to get them on the shank. They would neither go on nor crimp on either. Accidentally I discovered and later read that a common knowledge fix was to put a dab of lube on the base of the bullet and then the check. Well that was and is “bullet proof".
Machining sizing dies I researched the history of Lyman's H&I dies. These new dies as reported by Lyman's advertisement were now tapered to work harden and toughen the bullet during sizing. True, tapered die could work harden an alloy.
At some point I was asked , “how did I achieve such a taper also", it wasn't much but it was indeed slightly tapered discovered when I trying to fit the pin. I was confused for some time too. It was hard to figure out. Well is was the lathe bed, although massive it was twisted ever so slightly. It's leveled out now.
Hornady's are the first actual checks that I have ever seen that actually have a crimping annulus or ridge in the malleable dish shaped copper checks. Why not brass, I'll bet it too strong and tough, that is, brass has twice the tensile strength of copper.
Dating myself you say! I've got my Medicare card now, actually effective on the first. However, CBA has my birthday correct but the US Government well they can't seem to get month straight.
Still excellent shooting from our Canadian member.
Lesson learned?
Remember this,"if you can't fit it, feature it"
Charlie