Winchester 680 was discontinued in about 1980. It was used in small cases like the 22 Hornet or the 30 M-1 Carbine. If you can get some old load manuals from the late 70's, they will have data in them for 680. If that is not possible you can try some of the other powders with close to the same burn rate (at your own risk of course). You can find a burn rate chart here http://www.ramshot.com/powders/burnrate.php or at any of the powder data sites. Accurate 1680, Hodgdon H4198, IMR 4198 and Vihta Vuori N130 are some of the closest ones. START WITH THE MINIUM LOAD AND WORK UP SLOWLY. Hope this helps.
680 was designed for straight walled rifle cartridges like the 30 carbine and the 33 hornet, can also be used in the 357 maximum for silhouette shooting.
680
2% of 680 = 2% * 680 = 0.02 * 680 = 13.6
680
12% of 680= 12% * 680= 0.12 * 680= 81.6
24% of 680= 24% * 680= 0.24 * 680= 163.2
15% off of 680 = 85% of 680 = 680*85/100 = 578
680+250 is 930. 680 + 250 930
680
680
680 X 1/8 = 680/8 = 85
It is then 680 because 5 rounds up to 10