357 Magnum Powder Position sensitivity & Fillers

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.

If wanting such a light load, why frustrate yourself fighting the free airspace and lowered loading density of .357 brass?

Either use a bulkier powder, like Red Dot or Clays, or use .38 Special brass.

I never had any positive experiences trying to use case fillers in straight-wall cases.

Raises pressure, may not help accuracy. Does foul barrel.

Use 38 special brass. Or a bulkier, non position sensitive powder As outpost75 has suggested. Although I have never used it, I'm betting that trailboss would be a great candidate for this.

thanks for that write up, I found it helpful. have some 231 that I now know will need some assistance if I use it

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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.

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I ran a very similar test several years ago using the 45 Colt as the test vehicle. My results were the same as yours. I still don't use a filler though. I just shake the revolver a tudge for the first shot to level the powder in the case. It works well. I also do the same for cast bullet rifle loads when no filler is used. It's now a habit and I probably do it without realizing it for most every shot when shooting less than full power loads.

The best powder that I've found for lighter loads in a 38 or 357 case regarding ballistic uniformity has been Hodgdon's Tightgroup or Alliant's Bullseye.

This will probably be of no help . . . but . . .

As already mentioned, 38 special brass would probably work better. If you are flush seating the WC or nearly so - there is of course some "jump" due to the nature of the load and depth of seating. If you feel that is an issue, then you could seat the WC out further for less "jump". I have a couple containers of 700X but have never even tried it yet as I got it during the "shortage" in place of what I usually use. But as suggested . . . it seems like a bulkier powder would work better?

Outpost75,

If you read my post, you would know I didn't indicate any pressure problems and The use of the corn meal filler actually prevented leading with the bullet I am using. I tried 38 spl. brass, but the accuracy wasn't as good as with 357 brass and filler.

psweigle, I tried Trail Boss and the accuracy was terrible. I use Trail Boss in my 45 Colts and 44 magnum with great accuracy. For me it seems Trail Boss works best in larger caliber and larger capacity brass. So I don't feel a need to use fillers in the 44 and 45 calibers for lighter loads.

For light loads with uniform ballistics I'd second what Sharfschuetze said,use Bullseye or tightgroup. I get very uniform ballistics and excellent accuracy with Bullseye, even in 30-30 cases and no filler.