Just wanted to add to the knowledge base here, as there are quite a few opinions on this powder, with all of them being right, from a certain point of view. First, for those who don’t know, there are at least three lots, and the one I am shooting is a “fresher” one from GI Brass (48000). I’m still doing load development on this powder in the 358, and so far, a couple things “seem” to be the case. In this rifle - which is a Turk Mauser 98 - it seems as though you cannot get enough powder into the case to run into pressure issues. I’ve run this load “hot” into the higher published 4064 data with cast and jacketed (both 200 grains) and still not had “full” combustion of the powder. Quit a few unburned or charred kernels left in the bore after firing.
Now, on a whim, I loaded up 7383 with some old 175 grain round nose jacketed bullets in my 7x57 (also a 98, with a post-WW2 Belgium stepped barrel) and ran them downrange today. Combustion was much more complete, although there were still some unburned kernels, and accuracy hovered ran 1-1.5 in all six weights loaded. It’s important to note, this was simply a first run at the powder and bullet combo, using starting and lower-end published 4064 data, but several of the different powder weights showed promise. My observations with these would indicate you could run into pressure problems with the 7x57 case towards the max loads of 4064, unlike what I (and some others) have noted with the 358 case.
Based on what I’ve observed so far, this lot of 7383 MIGHT be optimal in certain cartridges and cases where a heavy bullet (or boolit) is being pushed, using the lower end of published 4064 data. I am going to move to a heavier boolit in the 358, as there are several members on here - Ben, I think, is one - who have fired some very fine groups with 7383 and the 358, with far heavier boolits. Perhaps this is a key to using this powder optimally. Bullshop has also used 7383 in 308, 35 Whelen, and (I think) 30-06 and reported it worked well.
As to the accuracy of the two guns, both have shot well with other powders, the 7x57 keeping a stout load of 4350 and these same bullets inside an inch at 100, and the 358 and these same boolits shooting into 2 inches at 100 with 19 grains of 2400.