Be sure to keep the locking pins,their respective holes, and the pivot trunnions clean and lubed with your favorite lube. I like grease. They will last a very long time with normal use.
As OB said, the shoulders pull the barrels back against the standing breech and relieve the load from the trunnions. I was wondering out loud one time as to why the replaceable shoulders would ever experience wear. I wondered out loud in front of the right person and he 'splained it to me. Brilliant engineering. Rich Cole told me once he had never replaced a set of trunnions, even though they too are replaceable. I guess that's why they don't wear much, if at all. I have seen the holes for the locking pins wear pretty badly on rental guns at ranges but they are probably handled poorly and rarely, if ever, cleaned and lubed.
