223 chambers have a shorter throat than 5.56 and Wylde is a split between them in simple terms. The 5.56 has a longer throat to run higher pressured ammo safely, the Wylde is more accurate yet still handles pressure better than 223.
The 760 probably has a very loose cut chamber.
The head space is set by the barrel extension, the barrel extension is screwed into the barrel and pinned, then the chamber is cut to match a bolt. Bolts are pretty close across the board and just looking at the loose chamber in your friends 760 shows how loose tolerances can be and still be safe. Not optimum but safe.
I prefer to run one bolt with one barrel due to how the bolt wears into a barrel extension. It's kind of like lapping the bolt to the barrel extension.
Last edited by TWR; 05/26/16.
