Kurt;
If you put a Stinger beside a regular long rifle, you will notice that the actual case of the Stinger is longer by a fraction of an inch.
This fraction can cause the case to start to engage the rifling in the match chamber..
I have the 880SQ also, and Marlin warns against using the long cased rounds such as the Stinger, Quick-shok and the new hyper velocity Aguils rounds in both the 880SQ and thae 7000...
As I noted in another thread, as of Christmas my Marlin 7000 has been passed to my #3 grandson. I was in the enviable position of getting ready to replace it with another .22 auto.
After reviewing everything available....I will probably go with another 7000...can't find such a combination of price/accuracy anywhere else.
The 7000 is so accurate that it shoots awfully close to my 880SQ...depending upon me and the day it may sometimes edge the 880SQ out.
If you do want extra power rounds..try the Velociters or the 31 gr Federal hypers @ 1550 fps.
Enjoy that 7000, it's a good rifle...