Welcome to ShootersForum, Ray. I think you'll find this to be one of the friendliest and most informative gun sites on the web.
Shoulder set-back is something your resizing die does when you full-length resize your cases. Headspace on rimless cartridges is determined by the distance between the rim and a datum line on the shoulder of the case. To ensure reliable function, you don't want your cases to exceed this dimension, or you will have a hard time closing the action. At the same time, if your resizing die sets the shoulder back too far, the case can be driven forward when the firing pin strikes the primer and what you wind up with is one symptom or another of excessive headspace.
If your rifle has a properly sized chamber (most do) and you full-length size your case, you will barely touch the shoulder each time, ensuring reliable function and no problems with excessive headspace. However, if your buddy's rifle has a chamber that is a little shorter, your rounds might not feed well. If his chamber is quite a bit longer, you might wind up with a headspace problem. Odds are neither will happen, but experienced reloaders keep brass separated according to which gun it was fired from, as that is the ideal brass to reload and fire from that particular gun.
In answer to question (3), yes....there is something you need to do: You need to go back to the basics and work up a safe load for your buddy's rifle, just like you did for yours. You can't presume that handloads which are perfectly safe in your gun will also be safe in his, particularly if you are anywhere near a maximum load. This is true even if you and your buddy have the exact same make/model of rifle.
I hope this helps answer the questions you have and I look forward to seeing your posts around the forum.
Shoulder set-back is something your resizing die does when you full-length resize your cases. Headspace on rimless cartridges is determined by the distance between the rim and a datum line on the shoulder of the case. To ensure reliable function, you don't want your cases to exceed this dimension, or you will have a hard time closing the action. At the same time, if your resizing die sets the shoulder back too far, the case can be driven forward when the firing pin strikes the primer and what you wind up with is one symptom or another of excessive headspace.
If your rifle has a properly sized chamber (most do) and you full-length size your case, you will barely touch the shoulder each time, ensuring reliable function and no problems with excessive headspace. However, if your buddy's rifle has a chamber that is a little shorter, your rounds might not feed well. If his chamber is quite a bit longer, you might wind up with a headspace problem. Odds are neither will happen, but experienced reloaders keep brass separated according to which gun it was fired from, as that is the ideal brass to reload and fire from that particular gun.
In answer to question (3), yes....there is something you need to do: You need to go back to the basics and work up a safe load for your buddy's rifle, just like you did for yours. You can't presume that handloads which are perfectly safe in your gun will also be safe in his, particularly if you are anywhere near a maximum load. This is true even if you and your buddy have the exact same make/model of rifle.
I hope this helps answer the questions you have and I look forward to seeing your posts around the forum.