Why do my older American 1100s feel so different to pick than the new one?

Your core swap test basicly settles it, and it matches what I've seen too. The feel lives in the core, not the shell. I've got a handful of older cores mixed in with my practice pile and the difference is obvious the second the pick touches the first pin. Older ones give you that clean, distinct click and a firm set point. Newer ones feel mushier by comparison, like the feedback is coming thru a pillow. As for why, I don't think anyone outside the factory knows for sure, but the usual theories floating around are spring changes and looser machining tolerances on the newer runs. The key pin chambers and the pins themselves seem to be finished a bit differently now, and some people swear the driver springs got softer, wich would explain the vague binding you feel on recent production. Could also just be batch to batch variance, since even within the same year I've noticed some cores that feel better than others.

On your worn pin theory, I'd rule that out. Locks that have been picked a ton usually feel worse, not better. Worn pins get sloppy, the set points get mushy, and you get more false sets from spools and serrated pins wearing unevenly. The crisp defined feedback you're describing is the opposite of what wear does. A core that's barely been touched is what picks like butter.

So no, you didn't just get lucky with pin sizing, though pin height variance is real and can change how a specific core feels. Production era genuinely matters with these. If you ever pull a core and rekey it yourself, keep notes on the date code stamped on the core versus the housing, because that's where the difference shows up, not in the body casting. And if you ever snag another lot of older stock, it's worth grabbing it. They don't pop up cheap once people figure out what they've got.

I ran into the same thing when I pulled a newer one apart to repin it, and what struck me was the inside of the plug. The pin chambers on the older ones I've had open look smoother, almost polished, while the recent production has more visible tool marks running along the chamber walls. wheather that actually changes the feel or just looks telling under a loupe I can't say for certain, but it lines up with what you're describing. My plan is to polish the chambers on one of the newer plugs with some fine abrasive and see if the feedback sharpens any, since that would at least narrow down whether it's surface finish or something deeper like spring rate.

I service a few dozen commercial doors a week and keep cores from job sites when they get swapped out, so I've got a stack of these from different years in a parts bin. The spring thing holds up in my experience. Pulled the drivers out of an old one and a new one last winter out of curiosity and the newer springs were noticeably lighter, you could feel the difference just compressing them with your fingers. Lighter springs means the pins seat easier but you lose that firm stop. Try picking with the keyway pointed at the floor versus the ceiling on each one, the old cores barely change, the new ones get noticeably easier upside down.

Funny timing, I was just going through my practice pile last weekend and sorted them by the stamped date codes. Same pattern here, the older ones just talk to you better. One thing I'm wondering though, has anyone tried swapping fresh driver springs from a donor core into a newer one to see if that sharpens it back up? I've got a couple dead cores I could harvest parts from and I'm curious if that's all it takes or if the machining differences mean you can't fully bring one back.

Update: I popped two cores apart after reading these. The chamber wall thing checks out, the older plug looks almost buffed inside while my new one has faint machining lines you can catch with a pick tip. Also tried the spring swap someone suggested, moved a driver spring from an old core into the new one, and the sets got way crisper. Now I'm curious if polishing the chamber on a new core would close the gap.