denton
Member
Here's a short video I made last week, showing how I work up loads using the PressureTrace and a chronograph. Hope you enjoy it.
http://www.youtube.com/watch?v=9phezChbKRI
http://www.youtube.com/watch?v=9phezChbKRI
With our test equipment in place, we began the pressure and velocity testing portion of this test. We first fired the reference ammunition provided by Lapua in order to verify the calibration of our equipment, an Oehler 43 Personal Ballistics Laboratory system. Our pressure readings were within 100 PSI of Lapua’s specification; this was determined to be well within acceptable limits. Having preliminarily established the accuracy of the system, and due to the relatively limited amount of the factory reference ammunition, we loaded a reasonably large amount of our own reference ammunition to approximate the factory pressure and velocity. This was done using new Lapua brass, Lapua 105 grain bullets and VihtaVuori powder. One of the test primers, which had previously shown a very high level of consistency, was selected to be used in our reference load. All primers were seated with the Sinclair tool which has proven to be the best tool for this purpose.
To the extent possible, SAAMI testing procedures were used as a guide for our testing. However, there are many variances from those procedures. Most notably our use of a strain gauge pressure measuring system (Oehler 43) rather than the SAAMI standard copper crusher or piezoelectric transducer method as both of these are beyond the scope of our budget and facilities. Further, as the 6BR cartridge is not covered by SAAMI standards, the exact location selected for placement of the strain gauge was based on our understanding of the principles involved and the study of similar cartridge specifications in the SAAMI guide. Despite these variances, we believe the results obtained to be reliable and repeatable. (See: Voluntary Industry Performance Standards for Pressure and Velocity of Centerfire Rifle Sporting Ammunition for the Use of Commercial Manufacturers, American National Standards Institute 1992, 1999).
Firing our reference ammunition showed it to compare quite favorably with the factory product in terms of consistency and met our goal of having a larger supply of reference/calibration ammunition. While our reference load was slightly lower in pressure and higher in velocity than the factory reference ammunition, it was within CIP specifications for the 6BR Norma and produced very consistent pressures. This difference is most likely attributable to our unavoidable use of a canister grade powder as the factory powder is not available to reloaders. The factory reference ammunition was subsequently used to check the equipment prior to each session and our handloaded reference ammunition was used before and after each test to ensure that external factors such as ambient temperature were properly accounted for.
All testing for this article was done with a Borden action with new Krieger 1:8" twist barrel, 30" long chambered in 6BR by Lester Bruno and stocked in a MAK Enterprises Tubegun stock. The scope used was a Leupold BR 24 with the Tucker coil spring modification. Accuracy tests conducted prior to the primer tests showed this to be a very accurate rifle for its intended purpose: prone shooting at distances of 300 meters to 600 yards. The load used for the tests is the same as our reference load except for the primers, these being the only variable element. Each test firing consists of ten shots. (More at link)