September 5th 2023Vertical dispersion test — Six primer types tested at 500 yardsDo primer types make any significant difference in accuracy? Answer: “maybe”. Here’s an anecdotal report that tracked the vertical variance between six different primer types. The tester is an experienced shooter and has a rifle that is very accurate. Four of the six four-shot groups were less than 2? at 500 yards. This test does not answer the question but it does suggest that you should try a few different primers with your match ammo. Here is a very fascinating test for the 6 BRA (Ackley 6mmBR) cartridge. James Phillips, an experienced benchrest shooter at long range, tested SIX primer types from 3 different manufacturers. James set his 500-yard target to help determine vertical dispersion. James then shot four-shot groups in order with each primer type. The chrono was used to record the speeds. The photo shows the results. James says: “I will retest the two best groups for accuracy and consistency, with 10 shots per group”. CLICK HERE to view the full-screen photo of the target. As you can see, all groups are impressive. CCI 400 primers were used to shoot the smallest groups (1.253?). CCI BR4 was next best (and very near) at 1.275? for four shots. The Remington 7.5 at upper left won the “flatline” award. There was hardly any vertical. Primer Brand Group Size Velocity Std Deviation Remington 7.9 1.985? 4 shot 2955 FPS 8 FPS 4.0 FPS Federal 205M 2.200? 4 shot 2951 FPS 11 FPS 4.8 FPS Sellier Bellot SR 1.673? 4 shot 2950 14 FPS 5.9 fps CCI 450M 2.34? 4 shot 2947 14 FPS 6.6 fps CCI 400 1.255? 4 shot 2950 3 FPS 1.3 FPSCCI BR4 1.275 4 shot 2949 fps 15 fps 6.9 fps CARTRIDGE : 6mmBR Ackley aka 6 BRA. The parent case is the 6mmBR Norma. The 6 BRA has been fire-formed for a shoulder angle of 40 degrees and a body taper of less than 1 inch. The capacity is increased but the neck is slightly longer than that of a 6mm dasher. The capacity is sufficient to reach the accuracy node of 2950+ FPS. Some shooters claim that the 6 BRA is a more forgiving weapon than the 6mm Dasher. The 6 BRA has a much easier time firing-form. TEST REPORT — Conditions and Shooting Method. Loading Method. Tester James Phillips posted the following report in our Shooters’ Forum.Conditions: The tests were conducted in the morning, over flags. The flags did not move or even twitch. I had the best conditions I could ask for. It was overcast, so there was no wind or mirage. There were no others, just me. Test Procedure: I shot each shot at my pace, and with my Nightforce 1555X scope centered as best as possible. I did not use round-robin. Each four-shot group of the same was fired at one time. Then I moved on to the next primer. All of my shots today felt perfect. It’s possible that I could repeat this test tomorrow, and it would be the exact opposite. We can chase it forever. But [soon] i’m going test the BR4 primer and 400 primer… to see which one has the best accuracy and consistency. I know I’ve weighed them as accurately as I can. During initial load testing, all groups were shot using 31.1 grains H4895. During initial loading testing, I decided to use the Sellier & Bellot prime as it was more promising than the CCI 450 magnum I also tried. I was surprised to see the higher ES, SD and vertical from that primer. [Editor: Pay attention — a shot from the CCI 450 is in the center of the black diamond, stretching out the vertical. The Rem 7.5, on the other hand, had virtually no vertical. I was 5-6 FPS over what I thought to be my optimum velocity, which was 2943-2945 FPS. I will test 5 shots at 31.0 and 5 at 31.1 and see how it goes. I can only assume that my velocities were higher due to higher humidity, and of course the temps were also 5 degrees warmer this morning. It wasn’t too far away but I noticed it.
Similar PostsTags: 6mm BR Ackley Primers. CCI Primers. Federal Primers. James Phillips. Long Range Testing. Rem 7.5 Primers. Vertical Dispersion.
