28 nosler , Sammi spec chamber, 26 inch 8.5 twist proof barrel. Clean barrel I did some preliminary load development while fire forming 105 new (annealed) nosler brass. I hit pressure at about 78.5 grains of retumbo, ..... 3070 fps with the 195 bergers. Shot good groups at 77.8gr (3030 fps) FL sized brass, bumped shoulder back .002 (.0015) neck tension. Loaded 13 rounds at .1 grain intervals. 77.0 to 78.2 (same can of retumbo, same package of fed 215 primers). First shot at 77.0 gr showed A LOT of pressure. Thought that was odd. Loaded a round at 76 grains still a lot of pressure Loaded a round at 75 grains still some pressure sign Loaded a round at 74.5….still pressure……..2930 fps HELP!