I need some help interpreting my data.
I am trying to find an accurate loading for my S&W 686+ with a PC Lee 358-158-RF bullet. The 868's cylinder throats all measure .3580 give or take .0001 either way and the bore slugs out at 0.3570inch. Five of the seven throats measure .3580 exactly. I started with H110 and my Shooting Chrony shows velocities all over the place. Here's what I've gathered:
Grains |
15.0 |
15.2 |
15.4 |
15.6 |
15.8 |
|
1195 |
1284 |
1165 |
1193 |
1289 |
|
1205 |
1297 |
1166 |
1245 |
1251 |
|
1199 |
1269 |
1262 |
1229 |
1303 |
|
1327 |
1293 |
1307 |
1340 |
1350 |
|
1279 |
1164 |
1129 |
1141 |
1267 |
|
1351 |
1347 |
1241 |
1236 |
1197 |
|
1319 |
1218 |
1239 |
1175 |
1344 |
|
1264 |
1305 |
1202 |
1267 |
1183 |
|
1346 |
1202 |
1172 |
1196 |
1242 |
|
1194 |
1191 |
1296 |
1246 |
1282 |
|
|
|
|
|
|
Average |
1,267.9 |
1,257.0 |
1,217.9 |
1,226.8 |
1,270.8 |
Min |
1,194.0 |
1,164.0 |
1,129.0 |
1,141.0 |
1,183.0 |
Max |
1,351.0 |
1,347.0 |
1,307.0 |
1,340.0 |
1,350.0 |
Standard Deviation |
65.6 |
59.4 |
60.3 |
55.1 |
55.3 |
Spread |
157.0 |
183.0 |
178.0 |
199.0 |
167.0 |
I was expecting a somewhat linear slope trending upwards. Obviously something went wrong so I loaded up ten cartridges double checking everything. The bullets were weighed out to a max spread of 0.8 grains. The casings were all Winchester head stamp and trimmed to exactly 1.28 inches with two quality calipers used to double check length of every case. The powder was weighed out by a Frankford IntelliDropper and each load was double checked on a 505 balance scale. Each drop was 15.6gr, give or take three-hundredths of a Grain. (I was impressed with the FID's consistency)
I shot five rounds through the 686+
686+ 6" |
Velocity |
|
1263 |
|
1269 |
|
1334 |
|
1233 |
|
1220 |
|
|
Standard Deviation |
44.2 |
Min |
1220 |
Max |
1334 |
Spread |
114 |
Average |
1263.8 |
|
|
A spread of 114fps. What the hell is this? An SD of 44. Bullturds. At this point either I am doing something wrong with my loads, or my 686+ is a turd. I pull out my Contender to double check the last five rounds.
Contender 10" |
Velocity |
|
1597 |
|
1579 |
|
1588 |
|
1600 |
|
1588 |
|
|
Standard Deviation |
8.3 |
Min |
1579 |
Max |
1600 |
Spread |
21 |
Average |
1590.4 |
|
|
Holy Hanna! Now that's what I'm talkin' 'bout! A spread of 21 and an SD of 8! I'll take that any day! But the velocity scares me. Every manual that I have access to says this should be sprinting at 1100fps - 1400fps. I am absolutely sure I loaded 15.6 grains of H110. The 686+ was in the expected range, but the Contender was... not.
What is going on?