Thanks Jim R for the tip. I thought of this but my thought was, yes it will retard the bolt rearward but I was worried it might speed up the bolt return tool much and throw out the timing and cause other problems. The other problem, it might not take much spacer to bind up the action spring and cause the spring tube to be torn out of the action, as its only silver soldered in place. I also know that the bolt must retract at least an 1/8 th of an inch after it locks open, so I can check spring bind.
So, I still would like a 12 ga magnum action bar sleeve to try first if anyone has one.
If you or anyone else has done the spacer with success, please let me know.
Thanks in advance,