Hi Keith,
With over 80,000 rds in my ballistic tunnel using a dual chronograph system of my own design that's both paired and calibrated to work together, good match ammo will have a velocity Standard Deviation in the 6 fps +/-1 fps range.
To get numbers this good, you're forced to use Eley Match/Tenex or Lapua Midas +. I haven't tested enough RWS R50/R100 to verify if they may have the quality control to match Eley/Lapua.
With that velocity SD, the corresponding velocity Extreme Spreads will range from 30 fps to 42 fps for 50 shot strings. With 25 shot strings like we shoot on a target, V ES's will generally average around the mid to high 20's.
If you use small samples in your testing (5 or 10 shot strings), it's not possible to quantify the quality of the ammo based on velocity statistics, and in any event, numbers this low won't show up on a typical target because velocity SD/ES isn't close to being the major source of dispersion in RF.
Hi Landy,
Thanks for posting your findings. I was wondering do you see any correlation between a seasoned barrel and a overly fouled barrel on how velocity is effected?
Remember, these are good stats for "real" match ammo using adequate sample sizes and not some of the crap that may have "Match" stamped on the box.
Anything much worse than these numbers will degrade target scores and group sizes, as well as being discernibly worse at distances past 50 yds/50 M.
Do some lots have better velocity stats than other lots? Yes, but in general there's not enough of a difference to fret over.
That being said, I have come across rare instances with both Eley and Lapua where someone apparently fell asleep on the production line and primer and/or powder charge variances somehow escaped quality control as well as the associated company's testing process for each lot produced.
Landy