Yes. This and the fact that we were between chronographs. I had given away a Lab Radar and had to wait on a new Garmin XERO to arrive. This took longer than we would like but we are always going to be thorough in checking a customer rifle. The velocities Tim provided are consistent for out test ammunition across a large sample of barrels. BTW, the cheek adjuster problem was something unrelated that Tim found while doing the acceptance inspection.
It's helpful to understand the realities of factory ammunition and the fact that they can't weigh charges as we do reloading. Below is a histogram of the charge weight variation in a lot of 6.5 Creedmoor ammunition loaded by a respected ammunition manufacturer for a Government end user. This ammo is supposed to be top shelf in performance and accuracy. The sample is 58 charges, so pretty high confidence level. Applying the +/-3SD rule you would expect to find 1.1 grains (yes, more than a full grain!) variation in the entire population. Interestingly, the histogram is asymmetric suggesting that at longer ranges you would expect to have a decent group center with two low shots for every high one (the flyers
). I re-metered the charges to +/-0.02 grains (1/50th the original variation) and seated the original bullets in the cases. Fixing the charge variation made almost no difference in the velocity behavior of this ammo. In my next test I pulled sixty bullets and discarded the original propellant then recharged the cases with H4350, the classic 6.5CM load. The next round of tests with two barrels was dramatic with the ES falling to 20-22 fps and SDs of 6 and 7 respectively. The accuracy was also significantly improved.
We are in a period where the ammo manufacturers are struggling with supplies of critical components just as we reloaders are. Yet they are still producing pretty damn good ammo. If you are getting 100+ fps velocity variation, you may want to have a closer look at the ammo. Following that, it is reasonable to look at the equipment. Chronographs require testing just like everything else if you are to have confidence in the results. I've shot over four of the Garmin XERO chronographs now and the consistency between the units is exceptional, and thus far I have not experienced a single error with any of them.
Charge variation histogram
View attachment 8326225 I will leave you a test group from the rechared 6.5CM. Original case, primer, and 140 HYB bullets. If you want the very best results you really do need to load your ammo and have some good tools.
View attachment 8326230 -Scott
