Thread: Sub calibre insert

I have been browsing trademe and the guncity website as you do in this no man's land time of year between Christmas and new years.
I came across these sub calibre inserts that fit into a 12ga shotgun, not a new invention I know.
But it got me thinking if you fired say a .45acp round from one of these, would the 12ga barrel beyond the insert act in some way as a suppressor?

My thinking being it would give the expanding gas somewhere to go before it erupts from the end of the barrel?
Any thoughts on how quiet a .410 fired from one of these would be? Thought it could be good for possums on the lifestyle block and keeping the noise down.

Interested to hear anyone's experience with these.