- Mar 9, 2011
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I'm currently working up a second load for a 6" barreled Ruger GP100 in 357 magnum. The first load I worked up last week was 125 grain Speer Gold Dot JHP with Alliant 2400 powder, and standard small pistol primers. Unfortunately even with a heavy crimp, the small pistol primers wouldn't ignite the 2400 powder, as it was fairly slow-burning.
The first three rounds I fired starting with the starting load, resulted in squib loads. The bullet was forced into the bore, and the power didn't ignite. After driving the bullet out with a wooden rod each time, I decided to use a faster-burning powder with the small pistol primers. I changed to Alliant Blue Dot, and continued to work up 13.0 grains of powder with an overall length of 1.586, and an average measured velocity of 1460 fps.
Last weekend, I found a reloading shop nearby that was pretty well-stocked with bullets, primers, and powder. Today I started working up a load for some 140 grain Hornady XTP JHP bullets with Alliant 2400 powder, and Winchester WSPM small pistol magnum primers. My reloading manuals gave varying data for that combination of powder, bullets, and primers, so I used the starting load that was supposed to result in the lowest velocity, and worked my way up .3 grains at a time. Normally a hand-loader would increase his charge by .1 grain at a time but in these times of scarcity, I opted for .3 grain increments because I knew I was well below the maximum charge.
The target velocity I wanted to attain was 1300 fps. The recommended starting load was 12.5 grains of Alliant 2400 powder and magnum primers, for a velocity of 1047 fps. In reality, that resulted in an average velocity of 1229 fps measured with a chronograph at a distance of 10 feet.
Working my way up to 13.7 grains of powder, I reached an average velocity of 1308 fps, which is what I wanted. The ignition was crisp and beefy, the cartridge cases exhibited no telltale signs of pressure, and the muzzle flash was awesome. I then continued to increase the powder charge in 0.2 grain increments, and noticed an anomaly. The velocity was not increasing and at one point I noticed slight indications that the pressure was increasing. One of the first signals of increased pressure is usually found in the spent primer. By the time I got to 15.0 grains of powder which is the maximum recommended load, I noticed some minor cratering in the primers, but the velocity had decreased to an average of 1240 fps.
What this shows is that sometimes you can reach a plateau or a flat spot, where increasing the powder charge doesn't increase the velocity. That usually means you're reached the "sweet spot" and at that point, it's best to decrease by a couple tenths of a grain and go with it. There are other tweaks you can do at that point, like adjusting the overall length if you're loading rifle ammunition. But this wouldn't make much difference with pistol calibers, unless you're loading 9mm, .40, or .45 ACP. That's because they headspace on the cartridge rim, and the ogive of the bullet should be a couple thousandths of an inch from touching the lands and grooves. I usually use the "plunk test" on semi-auto pistols by removing the barrel and seating a bullet until the cartridge turn freely with my fingers, and without any resistance.
The case on the left was from one round that measured around 1300 fps. Notice no signs of pressure in the primer. The one on the right was from the increased powder charge but decreased velocity. Notice how the primer was starting to crater. That's a sure sign you're getting into dangerous territory. Any further increase in the powder charge could result in an extremely-flattened or punctured primer or a cracked cartridge case. It's a good thing to know the signs of excess pressure if you reload your own ammunition.
The first three rounds I fired starting with the starting load, resulted in squib loads. The bullet was forced into the bore, and the power didn't ignite. After driving the bullet out with a wooden rod each time, I decided to use a faster-burning powder with the small pistol primers. I changed to Alliant Blue Dot, and continued to work up 13.0 grains of powder with an overall length of 1.586, and an average measured velocity of 1460 fps.
Last weekend, I found a reloading shop nearby that was pretty well-stocked with bullets, primers, and powder. Today I started working up a load for some 140 grain Hornady XTP JHP bullets with Alliant 2400 powder, and Winchester WSPM small pistol magnum primers. My reloading manuals gave varying data for that combination of powder, bullets, and primers, so I used the starting load that was supposed to result in the lowest velocity, and worked my way up .3 grains at a time. Normally a hand-loader would increase his charge by .1 grain at a time but in these times of scarcity, I opted for .3 grain increments because I knew I was well below the maximum charge.
The target velocity I wanted to attain was 1300 fps. The recommended starting load was 12.5 grains of Alliant 2400 powder and magnum primers, for a velocity of 1047 fps. In reality, that resulted in an average velocity of 1229 fps measured with a chronograph at a distance of 10 feet.
Working my way up to 13.7 grains of powder, I reached an average velocity of 1308 fps, which is what I wanted. The ignition was crisp and beefy, the cartridge cases exhibited no telltale signs of pressure, and the muzzle flash was awesome. I then continued to increase the powder charge in 0.2 grain increments, and noticed an anomaly. The velocity was not increasing and at one point I noticed slight indications that the pressure was increasing. One of the first signals of increased pressure is usually found in the spent primer. By the time I got to 15.0 grains of powder which is the maximum recommended load, I noticed some minor cratering in the primers, but the velocity had decreased to an average of 1240 fps.
What this shows is that sometimes you can reach a plateau or a flat spot, where increasing the powder charge doesn't increase the velocity. That usually means you're reached the "sweet spot" and at that point, it's best to decrease by a couple tenths of a grain and go with it. There are other tweaks you can do at that point, like adjusting the overall length if you're loading rifle ammunition. But this wouldn't make much difference with pistol calibers, unless you're loading 9mm, .40, or .45 ACP. That's because they headspace on the cartridge rim, and the ogive of the bullet should be a couple thousandths of an inch from touching the lands and grooves. I usually use the "plunk test" on semi-auto pistols by removing the barrel and seating a bullet until the cartridge turn freely with my fingers, and without any resistance.
The case on the left was from one round that measured around 1300 fps. Notice no signs of pressure in the primer. The one on the right was from the increased powder charge but decreased velocity. Notice how the primer was starting to crater. That's a sure sign you're getting into dangerous territory. Any further increase in the powder charge could result in an extremely-flattened or punctured primer or a cracked cartridge case. It's a good thing to know the signs of excess pressure if you reload your own ammunition.
