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?