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Old August 7, 2020, 11:09 AM   #1
BondoBob
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When to trim case length

Should I trim cases before or after re-sizing?

I have been having trouble with re-loading 380. After buying some better dies I find perfect results are only attainable with perfect case length. I've never had to trim 38/357 cases.

I've added the Lyman M expander die which mostly solved the problem along with the Hornady seating die with the bullet straitening feature.

But if the case is off by just a few thousandths too long it buckles the middle of the case after expanding, failing the plunk test. Sometimes the Lee FCD gets the rounds to pass the plunk test, but I can still see the substantial bulge in the middle. Is this OK?

These cases vary between .668 and .675 in length after resizing. This is a combination of new and once fired brass. I suppose trimming all will be faster and better than sorting by length or headstamp and then adjusting the die with each sort.

Last edited by BondoBob; August 7, 2020 at 11:31 AM.
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Old August 7, 2020, 11:18 AM   #2
pwc
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Is the bulhe from case buckle or bullet base bulge?
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Old August 7, 2020, 11:26 AM   #3
BondoBob
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It's case buckle, in the middle. The bulge appears after expanding with the Lyman M die before the bullet is even inserted.
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Old August 7, 2020, 12:12 PM   #4
7.62 man
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I don't trim straight walled cases, only necked down rifle brass.
I have found pistol brass doesn't stretch enough to worry about, unless you load it real hot.
Are you using the case mouth expander before seating the bullets?
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Old August 7, 2020, 12:40 PM   #5
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Bob, I see you have been reading the posts lately on straight wall pistol cases, you get it.
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Old August 7, 2020, 02:04 PM   #6
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To be clear, when you say "buckle" to me it means the case collapses, and folds inward.. Bulge and buckle are not the same thing

What brand cases? dies?

the Lyman expander die body doesn't touch the case at all. There's nothing to cause the case to "buckle", unless the expander is grossly oversized. (like shoving a .35 expander into a .270 case mouth. that will cause the case to buckle and collapse, leaving a section looking like accordian folds)

Some sizer dies squeeze the case down enough there will be a noticeable bulge where it is expanded, but that's not the case buckling, even if it seems to look like it.

I've expanded cases until the belling split the case mouth without ever having any case buckle. So, I'm, curious exactly what is happening.

As to trimming, you trim after sizing. You trim so cases do not exceed the maximum length, and for uniformity.

The point of uniformity is so that you don't have to constantly adjust your dies for different case lengths. Uniform case length means uniform crimps, which can matter alot. You can wreck a too long case in the seater die, trying to crimp where there is no room to crimp.
Cases can be bulged (and even collapse) to the point where they will not chamber.

I use Lyman and RCBS dies, I don't use, or even have a LEE Factory crimp die, never had a need or use for one.

My opinion is that, if you "need" a Lee FCD, then you are doing something wrong with the regular die set's adjustments.

Quote:
I have been having trouble with re-loading 380. After buying some better dies I find perfect results are only attainable with perfect case length. I've never had to trim 38/357 cases.
One more question, is the expander you are using the right one for the .355" bullets used in the .380?

.38/.357 are quite different from .380. Headspacing on the rim means case length isn't as critical as a case that headspaces on the case mouth. Roll crimp is different from taper crimp in several ways.

perfect results only attainable with perfect case length? so ensure your brass is the perfect length. It takes a little effort and concentrating on doing things just the right way, but its not impossible.
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Old August 7, 2020, 04:46 PM   #7
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Bob,

The SAAMI drawing says a .380 Auto case may be 0.670" to .680" long within the standard, and 0.675" will be the trim-to length, based on that. So your long cases are actually the ones that are the ideal trimmed size.

What is most likely causing the buckling is you have the expander adjustment on the M-die screwed too far in. It is also possible the adjustment shifted. The expander plug screws into the adjuster screw with the knurled head that you turn, and if it gets loose, it will try to push too deeply into the case. Loctite will put a stop to that problem if you have it. But either way, whether you need to set the die up again or you have a loose expander plug, the first step is to unscrew the adjuster all the way and check out the plug.

The setup on the Lyman M-die is slightly different from other expanders. Back the die body out of the press a couple of turns. Run the ram of your press up (handle all the way down) with just your shell holder in place. Turn the die body down until it just kisses the shell holder. Unlike a resizing die, it is turned no further in. Set the lock ring to keep the die body in this position. Now start the adjustment screw into the die. Put your longest resized case into the shell holder and run it all the way up. Turn the adjuster in until you just feel it touch the case mouth. Lower the ram and case.
At this point, the Lyman instructions have you nudge the adjuster in with partial turns until you feel the light resistance of the expander plug just starting into the case. You back the case out and turn the adjuster in another fraction and you just repeat those steps until you feel a significant increase in the resistance to the case going in. At this point you are at the first step. You then turn the adjuster in another 1/16 of an inch. Well, the adjuster threads are 18 TPI. If they had made them 16 TPI, you would just go in one more full turn. But with 18 TPI you need 1⅛ turns. But however you get there, that is all the expansion you are supposed to need.
For the .380 Auto SPECIFICALLY, I have a different adjusting method. Go back up one paragraph to where you just feel the expander plug kiss the case mouth as you turn it in. Then, lower the case. Put a pencil or Sharpie mark on the adjuster and turn it in exactly 4 full turns. With 18 TPI, 4 turns is 0.22 inches. Assuming your M-die profile is the same as mine, the first expanding part is 0.2" long and 0.22" will just get you onto the step a short distance. Now you can turn the adjuster in gradually to increase the depth of the step BUT DO NOT GO PAST 4½ TURNS (0.25 inches into the case mouth)!

That 4½ turns is a hard limit in the .380 Auto. Why? All pistol cartridges start getting thicker inside as you get close to the head. This is because the makers anticipate the case having to fire in a partially supported chamber, and the thicker brass prevents a blowout in the unsupported area. When I went through a bag of about 300 miscellaneous .380 cases, I used a pin gauge to determine where they start to thicken, and in all of them, it was just barely past ¼ inch into the case mouth. You do not want to let your expander go any deeper or it will start to expand the thicker part of the case. This will create a bulged ring around the case that prevents chambering.

Other case calibers start thickening at different places. .45 Auto typically starts at about 0.340" to 0.350" inches into the case. Shorter cases start sooner. This thickening also determines the maximum seating depth a flat base bullet can be inserted to.

So, what do you do if you follow the above instructions and still don't have enough expansion? First, chamfer your case mouths to see if that solves the problem. Then try calling Lyman. They may have slightly oversize expander plugs available. If not, you can always go for an extra operation by getting one of the inexpensive Lee Universal expander dies. This can be adjusted to add a flare to any case mouth if you need it. You could make the step first, then add the flare, or vice versa. You still want the step to keep bullets straight, but a small additional flare at the mouth will help them seat. This is no issue in rifle because there is no thickening to encounter, It should also be true for revolver cartridges, but they may the expander plug noses longer for them, so keep that in mind, and proceed slowly and carefully.

My own approach, if I were having an issue getting enough expansion would be to chuck the Lyman expander nose in my lathe and use a toolpost grinder to shorten it maybe 0.025" or so to let the flaring portion get deeper into the case.
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Old August 8, 2020, 07:55 AM   #8
BondoBob
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Thanks for the great feedback. I think I've got it working now.

I'm now sorting the brass by length. I ordered a trimmer for those cases that are not close to the others. A few were quite long.

I'm using the Lyman Neck Expanding M-Inchdie (380 Auto) for expansion. It is what was bulging (not buckling) the case in the middle.

For seating I use Hornady 044144 Bullet Seating Die, 3 .355" 380. The bulging was happening after expansion but before seating.

Last batch was 100% pass after backing out the die a bit and pre-sorting by length. Most rounds pass the plunk test with no crimp. But I'm using the FCD for now just for good measure and the odd one that is a bit sticky in the plunk test. I may sell that die when my technique improves to where I don't need it.

I'll locktite the M-die expander tip to the adjuster as I believe that may have been part of the problem.

It's a shame I had to replace 2 of the 4 dies from the Lee set. But it ended up costing about the same as a good RCBS or Hornady set so whatever. Both of the above dies can be used with my 9mm as well. So, I guess that spreads the extra cost out. I assume I'll have similar challenges with 9mm so now that's covered as well.
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Old August 8, 2020, 08:04 AM   #9
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As a followup to Bob's findings - is it common for brass of different manufacturers of a given caliber to be so far apart on their original case lengths as to cause this kind buckling issue?
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Old August 8, 2020, 09:02 AM   #10
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Even though you’ve solved your issue, it doesn’t hurt to use the Lee FCD. It is an excellent crimp die in its own right. Granted some use it to correct mistakes rather than eliminate the mistake, but that doesn’t negate its value as a good crimp die.
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Old August 8, 2020, 07:34 PM   #11
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Doyle,

The low pressure pistol cartridges don't generate enough pressure to stick a case to a chamber so they don't stretch. Indeed, they tend to shrink a little with each reloading and firing because they expand to the chamber diameter, which shortens them, but don't recover completely during resizing. By this mechanism, they gradually get shorter than the SAMMI minimum. I don't know the history of the OP's cases, so I don't know if some are short because of multiple reloading or if they just came from a manufacturer would was sloppy with the specs.
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