RS52 shortage

[ds1]

19 hours ago, Laurie said:

 

Yes, N140 and RS52 are fairly versatile (in common with nearly all tubular powders in that burn rate category), but it is more an issue of the three cartridges' case capacity to bore ratios, which are much closer than you might imagine.

The usual way to measure / categorise the ratio is to use capacity as measured in grains water weight and available either by measuring yourself using a fired and unsized case with the spent primer still in situ, or an approximate value as supplied by QuickLOAD or GRT, and dividing it by the area of the bore in square inches. This is the primary determinant of the optimal powder for that cartridge, a secondary one being bullet weight.   

 

308 ratio value is c. 750 (56gn water capacity divided by 0.075 sq in. bore area)

6BR runs at around 820

I can't be bothered looking up 22 Valkyrie's case capacity, but the slightly smaller 223 Rem runs at around 780 with my brass and rifle chamber, so is likely a tad over 800.

 

These lie, in the nature of this metric, very close, so need similar powder characteristics, hence RS52 and N140 work very well in all of them. As examples of quite different cartridges, .30BR runs at 527 and 30-30WCF at 587, so use faster burners to suit a low ratio; 7mm Rem Mag and 7mmWSM are both at 1,300 and need much slower burning magnum rifle powders to optimise performance. That 1300 figure is traditionally also taken as the dividing line for a cartridge being a true over bore-capacity design. Anything much higher reduces efficiency in terms of return on each grain weight of powder employed as well as going from being a 'barrel-burner' to being a serious barrel-burner.

It is not cartridge size per se that dictates powder needs. An easy way to see that is to look at a cartridge family based on a single case but necked up/down to different bore sizes and look at the powders advised in a reloading manual, and which produce the highest MVs. The most adapted design in current use is the 308 Win, since adopted in 6mm, 6.5mm, 7mm, .33 and .35 bores/bullets factory versions, and a few more wildcats too, but all 'same size' cartridges. 243 Win uses 'slower' powders than 308 Win which in turn uses 'slower' powders than .33 Federal for a typical bullet weight in each calibre.  

 

Thank you for the detailed reply Laurie. Years ago having half a dozen powders on the shelf was ok and I probably used more calibers back then and was more willing to experiment. I also hate getting stuck with half a lb of powder on the shelf that never gets used when I’ve given up testing it

These days I tend to buy in 10kg tubs and having just 2 or 3 powders is more economical.