Trimming Auto Pistol Cases is Unnecessary & Waste of Time So That’s What I’m Doing

My experience is that cartridges that seat on the mouth get shorter each firing. You may want to trim as long as your cases will let you - and probably sort by length. If you trim right on the listed trim lengths, after your next firing, cases will most likely be short.
 
I load mostly mixed range brass and with semi-auto pistol (9mm & 45 acp) I like to set aside lots ( 50 - 100 ) of similar case length and then trim that lot to a consistent length ... the reason is for somewhat consistent flairs , seating depths and then crimps with that lot . I adjust my dies for longer or shorter case lengths when needed .
But I find the first trimming to get everybody in the same ballpark is all that you need to do .
There will be a min. and max case length in the book ... I use a length in between ... not min. and not max but some where in the middle and also based on my shortest case in my lot of 100 .
9mm cases are all over the place ... finding 100 cases that are all the same or nearly all the same length is hard ... I buy once fired range brass in lots of 1,500 or 2,000 to sort through !

Same thing with revolver cases , get them all in lots of 100 with consistent trim length and then after that don't worry about it ... and some take it way too seriously about each case being Exactly X.XXX" long ... if one is a tad shorter or longer on the third decimal ... that's close enough !

And it's true ... after trimming they usually don't grow or they grow at a similar rate ... we talking straight walled handgun ammo here , no bottle necked !

So don't get all Anal-OCD and trim each time you reload a case ... Once and done will do fine .
Now if you like trimming and it makes you feel better by all means do it whenever you wish ...it does no harm .
Gary
 
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gwpercle said:
I load mostly mixed range brass and with semi-auto pistol (9mm & 45 acp) I like to set aside lots ( 50 - 100 ) of similar case length and then trim that lot to a consistent length ... the reason is for somewhat consistent flairs , seating depths and then crimps with that lot . I adjust my dies for longer or shorter case lengths when needed .
But I find the first trimming to get everybody in the same ballpark is all that you need to do .
There will be a min. and max case length in the book ... I use a length in between ... not min. and not max but some where in the middle and also based on my shortest case in my lot of 100 .
9mm cases are all over the place ... finding 100 cases that are all the same or nearly all the same length is hard ... I buy once fired range brass in lots of 1,500 or 2,000 to sort through !

Same thing with revolver cases , get them all in lots of 100 with consistent trim length and then after that don't worry about it ... and some take it way too seriously about each case being Exactly X.XXX" long ... if one is a tad shorter or longer on the third decimal ... that's close enough !

And it's true ... after trimming they usually don't grow or they grow at a similar rate ... we talking straight walled handgun ammo here , no bottle necked !

So don't get all Anal-OCD and trim each time you reload a case ... Once and done will do fine .
Now if you like trimming and it makes you feel better by all means do it whenever you wish ...it does no harm .
Gary
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Very helpful
 
CQB45ACP said:
Trimming Auto Pistol Cases ... 9mm & 45acp
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Don't ... Do ... It.

Straight walled semi-auto pistol cases like 9mm and 45ACP that need to headspace off case mouth should not be trimmed as repeated resizing and firing will shorten the case length over time due to resizing die carbide ring not reaching all the way down to case base.

After too many reloadings, resized case length can get short enough to start headspacing off extractor as chambered round won't seat case mouth with chamber.

CQB45ACP said:
Just ordered a Lee Deluxe Case Trimmer and dies for 9mm & 45acp.
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Cancel the order ... You will thank me later.

CQB45ACP said:
how do you determine an appropriate case length?
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As close to SAAMI lengths, longer the better.

If you want consistency, sort by resized length but DO NOT TRIM.

SAAMI lists .754" for 9mm case length and for my Lee Pro 6000 and 2023 Pro 1000 finished OAL consistency testing, I measured resized case lengths and chose .750" as typical average length to set my case mouth flare amount and taper crimp die adjustment (As longer case will apply more flare/taper crimp but didn't find too many of those as shorter cases were more common) - https://www.thehighroad.org/index.p...r-oal-consistency.911743/page-3#post-12446468
 
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I trim mine. I like uniformity. My rule is .010" range from min. to max. I always try to trim exactly to median .005" example. .40SW .850" Max length (measured) cut to my .845" I think its worth the effort.
 
PistoleroWadcutterGANG said:
LiveLife said:
After too many reloadings, resized case length can get short enough to start headspacing off extractor as chambered round won't seat case mouth with chamber.
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I trim mine. I like uniformity. My rule is .010" range from min. to max. I always try to trim exactly to median .005" example. .40SW .850" Max length (measured) cut to my .845" I think its worth the effort.
Click to expand...
Pull the barrel out of pistol and drop some resized/trimmed cases. If case rim is below the hood of the barrel, the finished round won't headspace on case mouth rather the extractor (Read far left comment in picture below "... Case Too Short ... Headspaces On Extractor") - https://www.thehighroad.org/index.p...rel-find-a-max-o-a-l-with-your-bullet.506678/

= DO NOT trim straight walled semi-auto pistol cases that headspace off case mouth =

index.php
 
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LiveLife said:
Pull the barrel out of pistol and drop some resized/trimmed cases. If case rim is below the hood of the barrel, the finished round won't headspace off chamber with case mouth rather the extractor - https://www.thehighroad.org/index.p...rel-find-a-max-o-a-l-with-your-bullet.506678/

= DO NOT trim straight walled semi-auto pistol cases that headspace off case mouth =

index.php
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Negatory! A lot of mfc. finished cases sold for reloading as well as factory ammo don't even come close to head spacing on the mouth ( even after sizing). Win cases out of the last bag i bought had 3 cases that were .847 length the rest greatly shorter. pull a few factory .40 cases and measure. Bet they don't come close to .850 length. They all loaded fine, and ammo fired fine and nobody knew, SO. Nice try on the troll though LIVE.
 
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PistoleroWadcutterGANG said:
Negatory!

Nice try on the troll though LIVE.
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I stand by my post
LiveLife said:
Pull the barrel out of pistol and drop some resized/trimmed cases. If case rim is below the hood of the barrel, the finished round won't headspace on case mouth rather the extractor (Read far left comment in picture below "... Case Too Short ... Headspaces On Extractor")

= DO NOT trim straight walled semi-auto pistol cases that headspace off case mouth =

index.php
Click to expand...
 
PistoleroWadcutterGANG said:
LiveLife said:
I stand by my post
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Good you do that
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Since you are new to THR and we have already discussed not trimming straight walled semi-auto pistol cases countless times, here's one more time why.

When chambered round is fired, case rim is pushed back against the breech wall face and expanding gas will push the case mouth out towards the chamber wall.

If case mouth is not in contact with forward part of chamber, more gas will leak around the case mouth until case mouth expands to seal with the chamber wall (Why we see Titegroup burn/soot on cases and dirty spent cases from blowback action PCCs). Trimming the case to make it shorter will push case mouth further away from chamber and likely leak more gas until case mouth expands to seal with the chamber wall. (I want my case mouth closer to forward part of chamber for less gas leakage)

While resized case length being same will produce more consistent flare and taper crimp amount and likely will push the bullet out the barrel, if you are looking for more consistency (Especially for match shooting), instead of trimming case length (Are you resizing before or after trimming?), sorting by resized but untrimmed length that is longest may produce more consistent chamber pressures.

Of course, just my humble opinion.
 
LiveLife said:
Since you are new to THR and we have already discussed not trimming straight walled semi-auto pistol cases countless times, here's one more time why.

When chambered round is fired, case rim is pushed back against the breech wall face and expanding gas will push the case mouth out towards the chamber wall.

If case mouth is not in contact with forward part of chamber, more gas will leak around the case mouth until case mouth expands to seal with the chamber wall (Why we see Titegroup burn on cases). Trimming the case to make it shorter will push case mouth further away from chamber and likely leak more gas until case mouth expands to seal with the chamber wall. (I want my case mouth to be closest to the forward part of chamber)

While resized case length being same will produce more consistent flare and taper crimp amount and likely will push the bullet out the barrel, if you are looking for more consistency (Especially for match shooting), instead of trimming case length (Are you resizing before or after trimming?), sorting by resized but untrimmed length that is longest may produce more consistent chamber pressures.

Of course, just my humble opinion.
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NAH, minutia important dictators. Trying to push a narrative. Fact ammo producers for the last 100 years or more have been more or less floating within this min max headspace game. Their ammo has been fine. Working for everyone without meeting your "IDEAL nonsense. A great number of National Precision pistol records were shot with ammo that did not hold to your exacting headspace dimension. Seriously go get a few boxes of the old national match ball ammo. take them apart. You will find the case length will vary and H.S of the extractor as you suggest, and everything will be just fine. Last also when in battery the extractor when made properly and clearanced will get pushed forward and move opening the bite on the rim just a tad when the breach is closed. Reliving the extractor head spacing and allowing the generous .010 space to soak up ammo of various lengths. No Live just no.
 
LiveLife said:
If case mouth is not in contact with forward part of chamber, more gas will leak around the case mouth until case mouth expands to seal with the chamber wall (Why we see Titegroup burn/soot on cases and dirty spent cases from blowback action PCCs).
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Why Titegroup and not other powders? What does this have to do with case length? Or is it a straight blowback thing?

More explanation for us dummies, please.
 
eddiememphis said:
Why Titegroup and not other powders?

More explanation
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Titegroup burns hot and violent. (Shoot enough rounds fast and you can literally sear steak on the slide ... or your hand)

So effects of gas leakage around the case mouth is more evident known as "Titegroup burn" expressed as black scorch mark on side of spent cases (But it cleans/polishes up well with dry/wet tumbling).

But I like Titegroup for 9mm as it produces more accurate loads than other powders and less temperature sensitive - https://www.thehighroad.org/index.p...itivity-manifest-itself.912670/#post-12465920

And if you are shooting a lot of rounds for groups (My range session could run several hundred rounds), it could be another variable as if you slow fire and keep a round in hot chamber, now you introduce added variable of powder temperature increasing that will effect pressure and muzzle velocity (And some powders are reverse temperature sensitive ... Slower velocities in hotter weather).

To keep my testing and powder temperature more stable, I keep my test rounds indoors and use cardboard box/ice chest at the range to keep them from getting hot from sunlight and hot/cold weather; as rounds left out on the bench could warm up unevenly from sunlight or cool down from storage/indoor temperature (On cold/frigid days) from start of range session to end.
 
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To directly answer your question I trim everything except auto cases... I choose a length to minimize total variation. I find .005 total as my goal. An example would be 357 where I trim to 1.280 and scrap anything shorter than 1.275. Obviously that means Hornaday is out completely...
 
SAAMI lists maximum trim length & minimum chamber length for 9mm, 45 acp. The number is rhe same.
I have trimmed 9mm Luger range brass that was over maximum. I trim it back to maximum. My 45 acp target load brass gets shorter, no trimming. Have corrected the rim diameter of max loaded 45 acps, after many firings.

Most chambers will be longer then maximum trim lenght, i would guess? Chambers can be measured.
 
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