Nate, yes you have to let all the air out of your bottle and take the regulator off.
I can't find a video as related to our Air Venturi tanks, but this video on the Ninja Reg is pretty thorough. Around the 8:00 mark he starts talking about the shims and taking one out on his particular regulator to reduce from an 800 psi output to a 700 psi output.
I'm pretty sure our air venturi set up works the same way, but we're gonna be reducing 1100 psi to what ever one shim will reduce it too. I'm just gonna take one out to start with, and try it that way. Then maybe take another out later?
I've got a new to me Wolverine B that I've been trying to warm up too and find the pellet it likes. This is the first ever high dollar airgun I've found that likes the cheap Crosman Premiers from Wally World? So, I've been busy with it lately and haven't touched the Sig.
I'll edit in another video if I find something better.
https://youtu.be/GttaRfu8KPg
Let me know how it goes!
Fuss