Weight sort to cure .357 vertical stringing?

[HathcockProtege]

Been trying to find a nice light target/varmint load for my 6" Ruger GP100 .357 Mag.

Today I tested a few light loads of Unique behind a 158g SWC and found that I had good (for me) accuracy at about 4 grains;5 shots in 2.8" CTC @ 25 yards.

I can live with this, but I couldn't help but be a little annoyed that my group was really tall and skinny; about 0.75" wide and 2.8" tall.

So, I'm sitting here @ my desk segregating about 300 "158 grain" hard cast SWC from an un-named company into (so far) three groups; 151-152g, 152-153g, and 153-154g.

Am I on the right track or should I look for some other solution?

Here's the load:

Winchester .357 Mag cases.
CCI 500 Small pistol primers.
4.0 grains of Alliant Unique.
"158" grain lead SWC; actual weight more like 153g.
RCBS carbide dies.
Moderate crimp.

Thanks in advance.

-The Kid.

 

[BK7saum]

Re: Weight sort to cure .357 vertical stringing?

Not sure of your experience with a revolver, but differences in grip from light to strong affect how much muzzle flip occurs before the bullet leaves the barrel. In barrel residence time is significant with a pistol or revolver. If you grip hard one time and not so hard the next, you WILL get vertical stringing. Also, try it over the chronograph. If you have a large extreme spread in velocity, it will affect vertical stringing also. You might want to refine your load to get more consistent muzzle velocities.

I think the last place I would look would be variance in bullet weights of 2-3 grains.

i just reread and noticed that your are using a moderate crimp. Are your cases trimmed to the same length. If not, variance in crimp can affect chamber pressures and also velocities (can result in vertical stringing).

BLK7

 

[HathcockProtege]

Re: Weight sort to cure .357 vertical stringing?


I am not a very good handgun shooter, but I didn't observe any vertical stringing with any of the four loads I tested with the Speer 146 grain JHP's in the same session; just the 158 SWC loads. So I don't think the problem is totally in my grip. I will definitely pay closer attention next time though. Thanks for the tip.

I must confess, I knew None of that about the crimp! I just measured 12 random pieces of brass and had variance from 1.265-1.280 in case length. Looks like I'll have to get the trimmer out and get to work, 'eh? Thanks man.

As to refining my load...I have a lot to learn. Just getting into this and my technique is still very rough, I'm sure. Hopefully get these loads over a chonograph in a couple weeks.

By the way, did you know it takes a long time to segregate bullets by weight using a Lyman beam scale? Just throwin' that out there...

-The Kid.

 

[ChadTRG42]

Re: Weight sort to cure .357 vertical stringing?

Yes, check the crimp. I can get large swings in group size and velocity just from the crimp using different length cases. If accuracy is the goal, you will need to make sure the brass is all the same length to get a consistant crimp. I don't know that a grain or two on a SWC bullet will make a difference. But I would group my cases into certain lengths, if they vary a lot.

 

[HathcockProtege]

Re: Weight sort to cure .357 vertical stringing?

Thanks dude.

How precise do I need to be in sorting the brass? I have lengths of 1.265-1.282. Would sorting within 5/1000th's be enough to make a significant difference?

I'd like to see 1.5" (CTC) groups @ 25 yards, if that helps.

 

[noahmercy]

Re: Weight sort to cure .357 vertical stringing?

My KGP161 (6" stainless GP100) shoots right at 1 1/2" at 25 yards with my Cowboy Action Shooting load. It's a 160 grain cast bullet over 3 grains of Titegroup in a 38 Special case. It only clocks about 830 fps, but that's very close to the load you have listed.

One other question is how you're benching your gun. If you're resting the barrel, that could be the problem right there. The barrel should NOT touch the rest, or vertical stringing can occur due to slight differences in applied pressure.

 

[HathcockProtege]

Re: Weight sort to cure .357 vertical stringing?

I didn't know that about resting the barrel. Wow. Guess I have a lot to learn.

I will say, however, that the four loads I tested with Speer's 146g JHP were all nice triangular groups using the same rest, so I'm not convinced it was entirely operator error. I'll definitely be paying close attention next time.

Just got done loading a batch of length sorted brass with unsorted bullets as well as vice versa.

Any other suggestions appreciated.

 

[noahmercy]

Re: Weight sort to cure .357 vertical stringing?

One other possibility is that you're getting big extreme spreads due to the position of the powder in the case. With that little propellent in that large a case, powder can lay to the front against the bullet, back against the primer, and any point in between, causing dramatic fluctuations in fps. This is why I use 38 Special cases for reduced loads. I reserve my Magnum cases for medium velocity or full-house loads where the powder will occupy at least 75% of the case.

You might try Trail Boss powder if you want mild loads using Mag cases. It is exceptionally bulky, but produces low pressures and velocities.

 

[HathcockProtege]

Re: Weight sort to cure .357 vertical stringing?

I had thought of using TrailBoss for that very reason, but, having heard a few horror stories of "delayed detonation" and ringed chambers due to too-light loaded .357 Mags, my thoughts were towards safety rather than accuracy. I want to stick to the .357 cases so I don't have to scrub the fouling ring out of my chambers every time I get done practicing and want to switch back to .357 Mag.

Guess I'll have to check it out next time I get to the range. May have to switch to TrailBoss for the practice loads eventually...I'll sure miss the smell of burnt Unique!

-The Kid.

 

[HathcockProtege]

Re: Weight sort to cure .357 vertical stringing?

Well, I went out again today and I must say, there wasn't a lick of difference between the weight sorted and the ones I sorted by case length. I rested only the butt/trigger guard of the gun on a sandbag this time and I my groups are wider and shorter over all. I paid a lot closer attention and think that it was my shooting technique more than anything else that was causing the vertical stringing. I'm convinced the load is more accurate than I am, so that's good enough for now. I need a day when the snow isn't blowing into my face and making me tear up so I can get a little better feel for what is load imperfections and just human error.

Just for kicks, I also loaded up a few with 5 grains of Unique instead of the 4g that I have been playing with and I'll check later to see if that helps me any.

Thanks for all that contributed. I learned a lot.

-The Kid.