Loading these first cartridges for my rifle really got my emotions rolling. When I loaded them I didn't intend to shoot them right away, and thought I would let my poor shoulder heal a couple more weeks. But holding those rounds in my hand was magnetism I couldn't resist. I got my courage up, and off to the range I went.
Ross Seyfried stated the formula for substituting IMR4198 for black powder. His rule is 40% to 46% of the weight of the original black powder charge. The chart of Eley ballistics reproduced in the back of Graeme Wright's book shows the .577 2 3/4" round loaded with 160 grains of black powder behind a 520 grain bullet yielded 1725 fps at 10 tons pressure. My bullet is a tad heavier.
40% of 160 would be 64 grains of IMR4198. 46% would be 73.6 grains. Those should be the approximate limits of loads using IMR4198, although I'm mindful of my heavier bullet. Thus I decided on my try-out load of 65 grains.
I anticipated this load would be on the light side. My prediction to myself was that the barrel groups would be spread apart 4 to 5 inches, and as it turned out my prediction was just about spot on.
I fired four rounds - two rights and two lefts at 50 yards. The result was two nice groups spread 4 inches apart and punching the target just to the right and just to the left of the base of the bullseye. Obviously the rifle is asking for a bit more horsepower. Not bad results for the first try!
The shoulder? That's another matter. A trying experience by any measure. Let's put it this way: There was no damage done, but I'm not running out to the range this afternoon to try 66, 67, 68, 69, and 70 grain loads as I would under normal circumstances. Maybe next week.