Hello,
I recently found the half dollar kennedy coins I used to practice with when I was a kid, some 20 years ago. I found they have a weight of 0.388oz or 11g and feel way less slippery then the kennedy's I recently bought at Blackpool with a weigt of 0.317oz or 9g and way more slippery then the "old" ones. Also the recent ones are more shiny. Any thoughts anyone?
I am wondering, are the recent ones reproductions? Can you still find the "old" stock?
Thanks

Well 1964 Kennedys were silver and there were some made with 40% silver. Those will look less shiny. It may be helpful if you would provide more information about your old half and perhaps a photo

Yes, the years would help a lot, especially for the older ones.
A quick check online: https://en.wikipedia.org/wiki/Kennedy_half_dollar shows that the clad coins (since 1971) are 11.3g. https://en.wikipedia.org/wiki/Kennedy_half_dollar).
I'm certain they're real - there's no purpose to making a fake coin like these when they're only $0.50 to buy.

Which your old ones were makes a big difference to how they compare. If you had ones from 1964, those would have been 90% silver, which would feel/sound different. ('65-69 was 40% silver, as Joshua mentions).

That said, I suspect your coins from ~20 years ago were just the older clad coins '71-'81. Sometime along the way after that (it was actually a gradual change) they altered the image from being high relief (like the silver coins) to a low-relief one, like on the coins you bought. This makes them more slippery for coin stuff, but also a bit quieter.

But if you really want the older ones, it's pretty easy to find them, depending on where you live. If it's in the US, just go to a bank, most will have some lying around they'll sell you, and the older ones are more common because they stopped minting the half dollars for mass circulation. If you're out of the US, try a coin store, which will probably cost you a little more, but they're still common coins so shouldn't be too much more than face value.

The strange thing is the rough dull ones are from 78, 79,84,and 89
the shiny slippery ones are all dated 71