03lover
04-06-2017, 03:20 PM
I ran into a problem when doing some load testing in my 357 magnum revolver.
I started noticing the first round of five shot groups was low and out of the group. I figured this was caused by my loading process. I was sitting and would have the revolver in my left hand, muzzle pointed down and to my left when loading. Then I raise the revolver up to the shooting position, level and barrel supported in the pistol rest and using a two hand hold, I would fire. I was shooting a 145gr. wad cutter/.358" diameter with 3.5gr. of 700x.
I concluded the first round had the powder forward in the cartridge and the next four rounds the powder was where ever the recoil left it. I decided to test my theory.
I fired a ten shot group with the powder positioned forward and a ten shot group with the powder to the rear. The group fired with the powder to the front was noticeably lower on the target than the group fired with the powder to the rear and no shots out of the group. This explained the first shot low problem.
Additional testing with 231, AA5 and 700x firing over a chronograph provided proof of what was happening.
All rounds fired with the powder to the front always had lower velocity than those rounds with the powder to the rear. The difference ran from 200 fps to 280 fps which is a very great difference when you consider these loads were only running about 700fps to 900fps for the 231 loads and near 800fps to 1000fps for the AA5 loads.
I also used three different primers for all the loads. There were minor changes in velocity with the changes in primer, but one thing held true with all the different loads, powder to the front velocities were always lower than powder to the rear.
Then I started to top these loads with corn meal. Just enough over the powder to fill the case to the base of the seated bullet with a very light compression. The groups shrunk to really nice groups with no more low shots. Another benefit was the minor leading I was getting with these cast bullets went away.
I also tested many of the powders other shooters claim to NOT be position sensitive. I found all those powders to have some sensitivity when the powder is most extremely different in position, front or rear. It was always enough to open up the groups, some more so than others. Bottom line, most casual shooting the differences probably won't be noticed. When bench rested load testing like I do, the differences can and do mess up the results of the testing. Please remember, this is using a 357 magnum and powder charges that fill the case to only about 1/3 leaving much room for the powder to shift position.
I either have to be sure to fire all rounds with the powder in the same position, to the rear is preferred or top off the load with corn meal. Other fillers can be used, I just don't like plastic ones.
I started noticing the first round of five shot groups was low and out of the group. I figured this was caused by my loading process. I was sitting and would have the revolver in my left hand, muzzle pointed down and to my left when loading. Then I raise the revolver up to the shooting position, level and barrel supported in the pistol rest and using a two hand hold, I would fire. I was shooting a 145gr. wad cutter/.358" diameter with 3.5gr. of 700x.
I concluded the first round had the powder forward in the cartridge and the next four rounds the powder was where ever the recoil left it. I decided to test my theory.
I fired a ten shot group with the powder positioned forward and a ten shot group with the powder to the rear. The group fired with the powder to the front was noticeably lower on the target than the group fired with the powder to the rear and no shots out of the group. This explained the first shot low problem.
Additional testing with 231, AA5 and 700x firing over a chronograph provided proof of what was happening.
All rounds fired with the powder to the front always had lower velocity than those rounds with the powder to the rear. The difference ran from 200 fps to 280 fps which is a very great difference when you consider these loads were only running about 700fps to 900fps for the 231 loads and near 800fps to 1000fps for the AA5 loads.
I also used three different primers for all the loads. There were minor changes in velocity with the changes in primer, but one thing held true with all the different loads, powder to the front velocities were always lower than powder to the rear.
Then I started to top these loads with corn meal. Just enough over the powder to fill the case to the base of the seated bullet with a very light compression. The groups shrunk to really nice groups with no more low shots. Another benefit was the minor leading I was getting with these cast bullets went away.
I also tested many of the powders other shooters claim to NOT be position sensitive. I found all those powders to have some sensitivity when the powder is most extremely different in position, front or rear. It was always enough to open up the groups, some more so than others. Bottom line, most casual shooting the differences probably won't be noticed. When bench rested load testing like I do, the differences can and do mess up the results of the testing. Please remember, this is using a 357 magnum and powder charges that fill the case to only about 1/3 leaving much room for the powder to shift position.
I either have to be sure to fire all rounds with the powder in the same position, to the rear is preferred or top off the load with corn meal. Other fillers can be used, I just don't like plastic ones.