LRF,
Are you sure the rifle is a 35 Zimmerman, and not 358 Enterkin Magnum? Is the barrel marked? Your description is spot on for the 358 Enterkin which is a proprietary cartridge made and marketed by my late friend Gene Enterkin. It was demonstrated in 1959(about)at Ft. Benning Ga. It, indeed does get over 3000 fps from a 250 grain bonded core rebated boattail bullet that Gene made before he died. At the time there were no 35 cal bullets available that would stand up to 3000 fps. Gene had his load data tested by HP White lab. With his bullets and 4064 powder. Of course, different lots of components could give different results. I believe his results exceeded the 358 STA, because he always used a longer barrel than the STA. After his death, I bought the pressure barrel and reamers/headspace ga., including for the 375 Enterkin(he hadn't finished the 375 when he died).
Mike
