Load Ballistics
Summary:
Zero 185gr JHC bullets and 8gr to 9.5gr charges of Power Pistol powder shoot small groups at 25yd (1.3"-2.5") and 50 yd (3.3"-4.6") from a new Ruger Blackhawk .45 Colt with 7.5" barrel.
Discussion:
Initial tests (Groups #868, #869) with Power Pistol (PP) and the Zero 185gr JHC .45ACP bullet (roll crimp, no cannelure) were promising with 25yd groups between 1.3" (9gr PP, 864 fps) and 2.5" (8gr PP, 738 fps) from the Ruger Blackhawk .45 Colt with 7.5" barrel. Shots were made with the revolver mounted in a mechanical revolver vise to remove human shooting error.
A second group of tests were conducted to determine the 50yd group size for an extended range of powder charges, 8gr, 8.5gr, 9gr, and 9.5gr of Power Pistol. This test was conducted to: 1) determine bullet performance at 50yd; 2) cross check group sizes be replicating one or more of the loads; and, 3) to determine if loads using Winchester WLP primers vs Fed150 LPP primers performed differently. Starline brass was used for all loads.
Point of impact of bullets on the target increased proportionally from low for low powder charges to high with higher powder charges. The maximum spread between groups shot from the 9.5gr load was approximately 7" higher than the 8gr load at 50yd. The revolver aim from the mechanical rest was not modified between groups. Ballistics calculations using standard curves suggest this difference should only be 2"-3", so some work needs to be done to understand this dramatic change in point of impact. One possibility is that the gun rotated up further with higher loads before the bullet left the barrel causing the point of impact to rise. Measuring the angle of the barrel after firing in the mechanical rest would be a measure of the pressure generated by the load.
The 9gr loads using WLP primers or Fed150 primers performed equally with 50yd group sizes of 3.7" and 3.6".
Replicated shooting of groups with 8.5gr powder were 4.6" and 3.3", and groups with 9.5gr powder were 4.2" and 3.3". Why this happened is unknown. Using different powders and bullets often result in shots stringing vertically which extends the group sizes. For both of these 8.5gr and 9.5gr loads, the horizontal width of the groups were: 8.5gr: 1.4" and 0.7"; and, 9.5gr: 2.1" and 0.7". In these cases, horizontal spread was 1/3 to 1/2 of the vertical spread, but both horizontal and vertical spreads decreased for the second replication. The mechanical rest is very rigid horizontally but allows the gun to rotate up, vertically, during the shot. Higher pressure causes the gun to rotate up more than lower powered shots. Chronograph records need to be examined to determine the relationship of bullet velocity to vertical point of impact on the target.
Data were collected to try to understand why groups of shots using a mechanical rest string vertically. The cylinder chambers, numbered 1 through 6, were recorded for individual shots, with each group shot with chambers in order from 1 through 6. Often, but not always, chamber 1 shot the lowest on the target for a group, followed higher by chambers 2 then 3. Chamber 4 often shot very high for the group, and chambers 4, 5, and 6 often shot as a high cluster, with chambers 1, 2, and 3 shot as a low cluster. However, each of these observed groupings is sometimes confounded by shots that do not follow these generalities.
Another issue that can cause variability among shots is powder position in the case. Groups #900, #901, and #902 were shot by pointing the revolver up, tapping the revolver to shake the powder toward the primer, lowering the revolver in the rest, and making the shot. Each of these groups were relatively small: 3.7", 3.3", and 3.3". Powder position in the case might explain why the second replicate group for 8.5gr and 9.5gr both reduce group size by 1.3" or 0.9", respectively.
Explanations that might explain the vertical stringing include: 1) warming of the cylinder and barrel; 2) reduced friction in the mechanical rest during group shooting; or, 3) possibly bullets that are jumping crimp causing less volume in the brass case thus increasing pressure. The latter possible explanation can be easily tested by measuring bullet overall length, before any shooting vs. individual bullet length just before each is shot in group order.
Performance
Load: #886
Powder: 8.0 gr Power Pistol
Bullet: 185.0 gr Zero JHC
Brass: Starline
Primer: Fed 150
Ruger Group: #868, Velocity: 738 fps, Count: 7, ES: 64, Group Size (in): 2.50, 7 shots @ 25.0 yds
Ruger Chronograph Velocities: 735,749,779,723,740,715,727
S&W Group: #919, Velocity: 668 fps, Count: 6, ES: 46, Group Size (in): 4.33, 6 shots @ 50.0 yds
S&W Chronograph Velocities: 682,679,657,677,677,636
Load: #892
Powder: 8.0 gr Power Pistol
Bullet: 185.0 gr Zero JHC
Brass: Starline
Primer: Fed 150
Ruger Group: #896, Velocity: - fps, Count: -, ES: -, Group Size (in): 2.90, 6 shots @ 50.0 yds
Load: #893
Powder: 8.5 gr Power Pistol
Bullet: 185.0 gr Zero JHC
Brass: Starline
Primer: Fed 150
Ruger Group: #869, Velocity: 864 fps, Count: 6, ES: 38, Group Size (in): 1.30, 6 shots @ 25.0 yds
Ruger Chronograph Velocities: 860,860,876,881,864,843
Ruger Group: #897, Velocity: - fps, Count: -, ES: -, Group Size (in): 4.60, 6 shots @ 50.0 yds
Ruger Group: #901, Velocity: - fps, Count: -, ES: -, Group Size (in): 3.30, 6 shots @ 50.0 yds
S&W Group: #916, Velocity: 750 fps, Count: 5, ES: 58, Group Size (in): 5.33, 5 shots @ 50.0 yds
S&W Chronograph Velocities: 767,719,756,730,777
Load: #894
Powder: 9.0 gr Power Pistol
Bullet: 185.0 gr Zero JHC
Brass: Starline
Primer: Fed 150
Ruger Group: #898, Velocity: - fps, Count: -, ES: -, Group Size (in): 3.60, 6 shots @ 50.0 yds
S&W Group: #929, Velocity: 830 fps, Count: 5, ES: 134, Group Size (in): 4.75, 5 shots @ 50.0 yds
S&W Chronograph Velocities: 766,812,817,856,900
Load: #896
Powder: 9.0 gr Power Pistol
Bullet: 185.0 gr Zero JHC
Brass: Starline
Primer: Win WLP
Ruger Group: #900, Velocity: - fps, Count: -, ES: -, Group Size (in): 3.70, 6 shots @ 50.0 yds
Load: #895
Powder: 9.5 gr Power Pistol
Bullet: 185.0 gr Zero JHC
Brass: Starline
Primer: Fed 150
Ruger Group: #899, Velocity: - fps, Count: -, ES: -, Group Size (in): 4.20, 6 shots @ 50.0 yds
Ruger Group: #902, Velocity: - fps, Count: -, ES: -, Group Size (in): 3.30, 6 shots @ 50.0 yds
S&W Group: #928, Velocity: 877 fps, Count: 5, ES: 166, Group Size (in): 3.13, 5 shots @ 50.0 yds
S&W Chronograph Velocities: 787,864,902,879,953