Depends wildly. If you fire form and only neck size, this will help considerably, but for small cartridges like your 204, you can get std devs low as 10fps. I have gotten as high as 100fps on my 300RUM or 338 winmag. Seems more powder, higher spreads. And you probably know, std deve is basically theaverage of the means. Or root mean square of the deviation from the means.