First my thanks for the help and knowledge shared here. I leave the following in the event anyone else pursues this solution.
I installed the Lakeside 11 inch recoil spring. The effort involved in retracting the charging handle was noticeably greater. I thought I should try it before attempting to trim it to function with a HV load. I loaded Remington golden bullet (RGB) into a magazine. after the first shot, I expected to have to charge manually, but it wasn't necessary. The RGB cycled without incident until it didn't.
Four shots in, I pulled the trigger, but there was no bang. My initial thought was "Shadowcop was right!". I looked at the bolt which was sitting half way between locked open and closed, and moved with little effort. I assumed the spring had broken.
Upon disassembly, I found that the end of the spring was a bit larger than the spring-stop ring on the CMMG recoil rod. It had snuck beyond that shelf and jammed itself and the recoil rod inside the spring guide channel at the top of the bolt.. After much effort and swearing and thinking I had put spring on backward, I clipped off the mangle end and reversed the spring. Three shot later, It had jammed the same way. This time, I used a small pair of pliers to reduce the diameter of the last coil at the end of the spring so that it was difficult to get back on.
RGB functioned and the bolt locked back on this essentially unshortened Lakeside heavy duty spring. Then the surprises came.
CCI mini-mag functioned and the bolt locked back.
Aguila HV functioned and the bolt locked back.
Aquila standard velocity functioned and the bolt locked back.
Winchester 45gr subsonic functioned and the bolt locked back.
Lessons I drew from this:
1. Before using a new spring on a CMMG recoil spring guide rod, inspect the rear end of the spring and be sure that it is tight around that end of the rod. If the spring slides onto the rod easily, it's too loose.
2. Standard springs seem to be calibrated either for quite short barrels or for heavier single stage FCGs, or maybe both. That the Lakeside kit comes with a lighter hammer spring seems nuts, but it must work for someone.