A .357 Mag headache

Regarding what jetinteriorguy and NoSecondBest said above, I did the following experiment today.

Procedure: 6 nickel .357 Mag cases:
1) Previously fired and cleaned, then measured
2) Resized and measured
3) Loaded with CCI 350 Mag primers, 2400 powder, 17.0gr to COL of 1.590”
(differences in COL may be due to case wall thickness, slight deformation of lead tip of the JHP, slight primer seating depth-??))

4) Fired each round and measured

5) Resized again and measured


Case Seated
Brand Fired Resized COL Fired Resized

1) R-P 1.275”1.280 1.581” 1.274 1.280

2) Win 1.285 1.296 1.588 1.285 1.297

3) WW Super 1.287 1.289 1.588 1.284 1.289

4) Win 1.287 1.292 1.590 1.286 1.292

5) WW Super 1.280 1.285 1.591 1.279 1.285

6) Win 1.292 1.297 1.588 1.291 1.298


I also loaded 5 more rounds without measuring the cases at all, with a target COL of 1.590”.
There was no discernable difference in accuracy between the two groups, shooting from a revolver rest at 15 yards. This would confirm what our two colleagues posted!

Sorry the table didn't come out right. I edited it twice but I think one can follow the data as it is.
 
In simple terms when you squeeze something (reduce the diameter) it gets longer. Roll some clay in your hands to make it thinner, and its gets longer as well. Stuff has to go somewhere.

SO, its not stretch from firing so much as from being resized.

And when seating and crimping bullets, the bullet isn't moving when the crimp is applied, the case is. The bullet is stopped and held in place by the seating stem, it is the final movement of the case being pushed up over the bullet when the roll crimp is applied.

I check for length but rarely trim, but rarely isn't never...
 
I had 80 .357 Mag cases back from the range that needed processing. I did just that today. I don't know their dimension prior, but they must have been <1.283" or I wouldn't have loaded them.

I resized and flaired; then measured. 8 were out of spec (>/= 1.283"). So 10% of them "stretched" out of spec somewhere in their loading/shooting/reconditioning cycle. 7 of the 8 out of spec cases were 1.283-1.285"; one was 1.286." All were Starline non-nickel. All were shot from a S&W 686 4" bbl. There was no less than three different load recipes in that batch of cases coming back from the range.

Not sure how much value that has. But that was my most recent experience and it's typical.
 
Once you flair them it’s too late to get an accurate length measurement. I don’t know anyone who measures flailed cases for length. They have to be measured as they come out of the sizing die, not the expander die.
 
My old Lyman manual lists max case length at 1.290" and trim to length at 1.285".

And the max overall loaded length is listed as 1.590".

With the bullet seated to the cannelure or crimp groove, how much shorter than the max length to exposed part of the bullet comes to isn't terribly important.

How much shorter than Max loaded length can matter to feeding in a rifle or semi auto, but not in a revolver or single shot.

If you want to use only one set of adjustments to your dies, (lock it in and leave it) you need uniform length brass. This means measuring and, yes, trimming to create uniform batches.

Otherwise, you need to load each round as an individual, backing off and readjusting dies for each one, to allow for differing case lengths.

I've done it both ways. Sometimes, I just like playing with my tools...;)
 
Once you flair them it’s too late to get an accurate length measurement.
Click to expand...

Maybe. But I'm not actually interested in an accurate length measurement. I'm interested in trimming the cases to a consistent enough length to get a consistent crimp. It works.
 
The SAAMI spec for case length is 1.290-0.020". That means 1.280" will be the middle of the length range which is commonly what is recommended for use as the trim-to length, the idea being to provide maximum latitude for errors in trimming in either direction. That said, you can't put trimmed metal back very easily, and given that this round is prone to case mouth splitting from heavy roll crimps working the brass, you could certainly start with them a little longer (1.285") and then, when the first few start to split, trim the rest back 0.01" to see if you can get a little more life out of them.
 
I'm interested in trimming the cases to a consistent enough length to get a consistent crimp. It works.
Click to expand...

I too never trimmed straight wall revolver cases...until I bought a cpl hundred Starline .357 Magnum cases. On first loading the crimps were all over the place...just a bad cut cycle in manuf. I guess. I trimmed them back to the Lyman suggested length AFTER sizing as No 2nd Place has suggested, and was rewarded with uniform crimps. I now trim all of my straight wall to a uniform length, once, after the initial resize...and yes, I do resize new brass prior to trimming. YMMv but I find that it helps.

It's a 5 minute operation to do a box of 50 on my shop drill press with a Lee trimmer mounted in the chuck. I also mount the chamfer tools in the chuck for a quick clean up of the mouth edge.

Rod
 
You have identified process variation. Case length affects crimp and crimp affects seating. You have also identified the cost of Quality. To trim every loading cycle creates a lot of work and to manage your cases as groups by headstamp, trim length, etc is also work.

The thing missing is what does this work do to improve groups on paper. Well, not much by my standards, but it might be enough for you.

I sort cases by headstamp and put in plastic boxes of 100. Then I fl size a box measuring the CL of the first 20. I set my seater and crimp dies with average length case. I crimp in a separate step. I check that crimp for movement by measuring if a sixth rounds oal moves.
 
My old Lyman manual lists max case length at 1.290" and trim to length at 1.285".
Click to expand...

The last 500 Starline brass I bought just this Spring had a couple dozen that were 1.290 and shorter, but most were a little over 1.280 so I trimmed them all to 1.280 and you will only have to trim them once.

I do a lot of roll crimping to and I don't like the roll crimp die pulling bullets in deeper when I'm loading max loads.
If your die is set up for a longer case and you run a shorter case through it and roll crimp it, the roll crimp will hit the lower end of the cannular and has no where to go so it pulls the bullet in deeper in the case.

When they are all the same length I don't have to worry about that.

If I'm just loading practice loads with plated bullets in mid range .357 Mag then I just use a taper crimp die. But I'm not separating all my brass in to different length lots just to be able to get enough for my hunting loads which are roll crimped. I can pick up any of them, since they are trimmed and use them for any load I want.
For me it is well worth trimming them.
 
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