For the past 2 years, I've been doing a LOT of shooting indoors..
For my backstops, I use something called "Stall Mat"
It's 3/4" thick rubber, but, I've only seen it come in Big sheets..
Tractor Central Supply is where I get mine..
A 'spinner' could easily be made by using little chunks of this stuff..
Thread it onto a rod, bolt it onto an existing metal target, etc.
It takes some Serious abuse, and it's relatively quiet when impacted.
I whack the stuff with .22 cal non stop and have gone up to .25 cal
^^^
I used to double it up, so in that frame, there's 2 layers.
Then after blowing through it with .25 cal,
I add a 3rd layer now - Just to be 'safe'. lol
Link if interested:
https://www.tractorsupply.com/tsc/product/4-ft-x-6-ft-x-3-4-in-thick-rubber-stall-mat 
Sam -
PS: If it's quiet enough not to drive me nuts indoors at only 10 meters,
I'm sure it'll be more than quiet enough for anything else it's used for.