Howdy,
This may, or may not, give a bit of help.
http://rimfirebenchrest.com/articles/Calfee-StoppedMuzzle.html
These are a collection of Bill Calfee posts from this site, from years ago. It's lengthy, but you'll see that in one of his posts he talks about waiting a bit of time and shots going high and left. This is a snippet of some of the posts.
"Earlier I described a rifle I'm building and testing......I played with the muzzle device and got it shooting pretty darn good.....but, like I said, the muzzle wasn't stopped......how do I know this?
I set the rifle up in my rest, that will RTB very good......I fouled the bore with a couple of shots, then moved to an aiming bull........shooting conditions were excellent...
I then fired three rounds RTB as quickly as I could.......but, I did not eject the case from the third round.......I lifted the bolt handle, withdrew the bolt enough to pull the case out of the chamber, which broke the seal between the case and the chamber. There is a chimney affect through the bore of a rifle barrel.......I waited a couple of seconds, then pushed the empty case back into the chamber and closed the breech bolt......if I would have ejected the third case and loaded the forth, I'd broken the seal to the bore......
At this point the forth round is standing in the loading block....cool.....
I waited about a minute, then ejected the third case, inserted the "cool" forth case, pushed the rifle forward and fired.....
I ran this procedure 10 times......3 times the forth shot did not enlarge the group.......7 times the forth shot was a flipper, usually high and slightly left....
Based on this test, the muzzle of this little rifle is not stopped.....in other words, as it is, this little rifle will not wait for me......
There's more to the story.....I'll finish when I get some more free time...
*****
I have a new idea that uses the water which forms in the bore after a shot has been fired that looks like it may be the best indicator of all in determining if I have my muzzle stopped.....
*****
I think I've maybe got a new way to tell if our muzzles are stopped....
I've been shooting two rounds, then waiting for a minute, then firing another round.......I'm finding if the muzzle device (some call the thing a tuner) is set correctly, my third round goes in the group.......generally...
If my muzzle device is not set correctly, that third round is a flipper......most of the time.....
*****
Muzzle device folks: Fire two rounds, wait a minute or two. then fire the third.....
Did the third round center the group?
If not, adjust your muzzle device, then repeat the test......
My dear friends, I ain't got all the answers yet, but, when you get your muzzle device set so that the third round centers the group, after waiting a minute or two........you have stopped your muzzle....oh yes you have... "
Read the entire link and perhaps you may find some benefit. These posts are from June to July of 2008. I think this was early on in Bill's figuring out his water in the bore testing. Hope this helps.
Take care,
Greg
Edit: It took me awhile to make my post, I didn't realize Tony had posted prior to me. Between Bill and Tony there's not a whole lot that's not known about shooting.