This may be a bit deep for new reloaders, but it should be read by everybody.
Here's the scenario; I was loading for a new-to-me 300 win mag. In fact I had never loaded for a win mag before. I was supplied with the rifle, brass fired in that rifle and new dimension Hornady dies. Also a lee trimmer pilot.
Looking at my powder selections, I saw a ¼ pound bottle of H-4831 SC, which is what I wanted to use. I also looked at the Hodgdon website for some ideas for what other powder types were on the data chart. I saw H-hybrid-100-V. Also IMR-4007-SSC. A visit to my local gunshop that has the best selection of powders in the area showed me no H-4831-SC, but the 100-V AND the IMR-4007-SSC. I bought a pound of each.
The bullet for this load would be the new Hornady GMX, 165 grain.
I settled on the 100-V, loaded 4-5 shot groups of one powder charge, starting mid-range in the data. Meaning I didn't start at recommended starting load,(66.0). GMX bullets are expensive, so I didn't want to waste any. 69.0, 70.0, 71.0, 72.0 were the loads. First the targets, then the chronograph data.
What would JUST the targets tell you? Not so good as far as groups, but the 70.0 group showed vertical stringing, a sign the powder burn rate is very wrong for the cartridge. Now the chronograph readings really tell "THE REST OF THE STORY"!
69.0 2 shots recorded, was off to the side and too close to the screens.
av 3099
hi 3100
lo 2999
es 1.3
sd .9
70.0 5 shots
a 3240
h 3269
l 3216
es 52.9
sd 19.8
71.0 5 shts
a 3230
h 3263
l 3198
es 64.1
sd 32.8
72.0 2 shots
a 3189
h 3194
l 3180
es 14.2
sd 10.1
The purpose of all this is to point out the usefulness of a chrono when developing loads. AND what happens when you reach the upper pressure limit of a powder The reverse readings are indicative of reaching, and in this case exceeding the pressure ceiling of a powder-bullet-primer-rifle combo. Primers used were rem. 9½-M. Bullets were seated to the top of the front band, 3.340 OAL.
Another indication of excess pressure is primer pocket expansion, to the point where the fired shell will NOT hold a primer. Both the 71 and 72 grain brass cases would NOT hold a primer, and primed with almost no effort.
A third indication of pressure is CHE and PRE, Case Head Expansion and Pressure Ring Expansion. I miked the area just ahead of the belt with my mic capable of .0001 accuracy. The 69 and 70 grain loads were the same as the once fired factory brass I was given,(Winchester). The 71.0 was .0003 MORE than the factory, and the 72.0 was .0005 more. That's a pressure ring measurement.
It's apparent that the Hodgdon hybrid 100 V is too fast for this particular load. It MAY be the extra tough bullet engraves harder, raising pressure. Could be almost anything, but how would I know without the chrono?
You SHOULD get a steady incremental climb in velocity with each even increase in powder charge. When the increase slows down, or as in this case reverses, you're into the danger area. Bolt lift was normal, which surprised me. The rifle is a Herters U-9, which is a FN mauser action.
Another load work-up using AA,(accurate arms) 4350 yielded what I was after, Max velocity,(3289 fps), with a 1" 3 shot group @ 100 yds.
Here's the scenario; I was loading for a new-to-me 300 win mag. In fact I had never loaded for a win mag before. I was supplied with the rifle, brass fired in that rifle and new dimension Hornady dies. Also a lee trimmer pilot.
Looking at my powder selections, I saw a ¼ pound bottle of H-4831 SC, which is what I wanted to use. I also looked at the Hodgdon website for some ideas for what other powder types were on the data chart. I saw H-hybrid-100-V. Also IMR-4007-SSC. A visit to my local gunshop that has the best selection of powders in the area showed me no H-4831-SC, but the 100-V AND the IMR-4007-SSC. I bought a pound of each.
The bullet for this load would be the new Hornady GMX, 165 grain.
I settled on the 100-V, loaded 4-5 shot groups of one powder charge, starting mid-range in the data. Meaning I didn't start at recommended starting load,(66.0). GMX bullets are expensive, so I didn't want to waste any. 69.0, 70.0, 71.0, 72.0 were the loads. First the targets, then the chronograph data.
What would JUST the targets tell you? Not so good as far as groups, but the 70.0 group showed vertical stringing, a sign the powder burn rate is very wrong for the cartridge. Now the chronograph readings really tell "THE REST OF THE STORY"!
69.0 2 shots recorded, was off to the side and too close to the screens.
av 3099
hi 3100
lo 2999
es 1.3
sd .9
70.0 5 shots
a 3240
h 3269
l 3216
es 52.9
sd 19.8
71.0 5 shts
a 3230
h 3263
l 3198
es 64.1
sd 32.8
72.0 2 shots
a 3189
h 3194
l 3180
es 14.2
sd 10.1
The purpose of all this is to point out the usefulness of a chrono when developing loads. AND what happens when you reach the upper pressure limit of a powder The reverse readings are indicative of reaching, and in this case exceeding the pressure ceiling of a powder-bullet-primer-rifle combo. Primers used were rem. 9½-M. Bullets were seated to the top of the front band, 3.340 OAL.
Another indication of excess pressure is primer pocket expansion, to the point where the fired shell will NOT hold a primer. Both the 71 and 72 grain brass cases would NOT hold a primer, and primed with almost no effort.
A third indication of pressure is CHE and PRE, Case Head Expansion and Pressure Ring Expansion. I miked the area just ahead of the belt with my mic capable of .0001 accuracy. The 69 and 70 grain loads were the same as the once fired factory brass I was given,(Winchester). The 71.0 was .0003 MORE than the factory, and the 72.0 was .0005 more. That's a pressure ring measurement.
It's apparent that the Hodgdon hybrid 100 V is too fast for this particular load. It MAY be the extra tough bullet engraves harder, raising pressure. Could be almost anything, but how would I know without the chrono?
You SHOULD get a steady incremental climb in velocity with each even increase in powder charge. When the increase slows down, or as in this case reverses, you're into the danger area. Bolt lift was normal, which surprised me. The rifle is a Herters U-9, which is a FN mauser action.
Another load work-up using AA,(accurate arms) 4350 yielded what I was after, Max velocity,(3289 fps), with a 1" 3 shot group @ 100 yds.
It IS a very solid rifle, since Herters has not been in business for 20+ years, it's at least that old. No signs on the case head, like ejector flow, or headstamp smears.