Magnetization measurements have been carried out on samples prepared with varied Sn contents, using constant parallel applied field sweep rates in the range of 30 to 190 mT/s. The hysteresis loops observed up to about 6 T at 4.2 K are earmarked by characteristic flux jump phenomena. J/sub c/ critical current densities deduced from the loop widths can be interpreted, in agreement with the fine analyses of the loops, in terms of global critical screening currents, related to very good connectivity between the grains.