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Old September 2, 2011, 10:28 PM   #1
GregInAtl
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Trim To Length Question

My Lyman 49th manual says that the trim to length for a .45 ACP cartridge is .888. However, the drawing shows it to be .898.
  1. Which is correct?
  2. I have several used cases that have been fired once that measure .885. Are these too short and need to be thrown out?
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Old September 2, 2011, 10:36 PM   #2
Rifletom
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No. You are good to go. Just make sure that your OAL is good for your gun[for feeding].
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Old September 2, 2011, 10:49 PM   #3
engineermike
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The .898 is the SAAMI length, and the .888 is the length that case was trimmed to when the bullet was tested for the load data and the .885 is the length of the case you picked up. I am not sure if the case shrinks when it is fired for the first time or whether the factory that made the bullet the first time trimmed the case to that length but as rifletom says "you're good to go" just keep your C.O.L. within specs. All of my 9mm, S&W 40's, and 38 specials are all shorter than the case trim length shown in the load manuals I have and they all work just fine.
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Old September 3, 2011, 05:27 AM   #4
GregInAtl
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How much tolerance should be allowed? That is how much is too short or how much can you deviate from the SAAMI length. Same with OAL, how close due you have to be to the OAL of 1.275 stated in the load book
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Old September 3, 2011, 07:17 AM   #5
Bailey Boat
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Bear in mind that the 45 ACP (in a semi auto) headspaces on the case mouth. Too short and the round may misfire, too long and it won't allow the slide to fully go into battery. You need to determine what your gun "likes". The measurement from the manual is usually correct and thats what I use 99.9% of the time.
If the rounds are going into a revolver using clips then you have more leeway since the headspace is now transferred to the rim.
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Old September 3, 2011, 07:43 AM   #6
m&p45acp10+1
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In over a year and half, I have as of yet in well over 40k rounds of .45 acp had to trim a single piece of brass. Very few reloaders will trim pistol brass. Those that do usualy load for revolver, and trim to a uniform length for crimping purpouses.
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Old September 3, 2011, 08:11 AM   #7
JimPage
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Staight wall cases don't lengthen like bottle neck cases do. It's unusual to have to trim straight wall cases. Bullet seating is not an issue if you taper crimp.
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Old September 3, 2011, 01:03 PM   #8
CherokeeT
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Been reloading 45 ACP since late '50's, never had a case too long or too short in the many thousands reloaded. Never trimmed any. 45 ACP caes do not seem to grow longer with use. YMMV
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Old September 16, 2011, 06:32 AM   #9
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Ditto on never having had to trim .45 ACP. Seems like the long out of print NRA book, "Handloading" had a good discussion on uniform head space and its effect on accuracy in the .45 ACP. Rod
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Old September 16, 2011, 06:51 AM   #10
Gary Wells
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In my experience, .45 auto cases will continue to shorten as they continue to go through the clean, load, & shoot cycle. If you trim them, you are just shortening your case life expectancy.
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Old September 18, 2011, 08:47 AM   #11
Walkalong
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I have never trimmed a .45 ACP case over many years and tens of thousands of rounds.
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Old September 18, 2011, 08:57 AM   #12
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Bailey Boat, how does a short case misfire?
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Old September 18, 2011, 02:22 PM   #13
Walkalong
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If the case is too short, and the bullet does not contact the rifling holding the case back, and the extractor doesn't hold the case back, it can go forward enough that the firing pin cannot set the primer off.
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