9mm case length

johnnyreb65

johnnyreb65

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I've asked before about going below trim to lengths in .223 and was told no worries as many trim below it so it won't have to be done again during the case life.Now I'm starting to load 9mm and .40. This is what concerns me..for BOTH 9mm and .40 the manual issues the following warning.

this cartridge headspaces from the mouth and therefore case trimming must be uniform and accurate. Do not reduce cases below the trim to legnth


I'm starting to setup my 550 for 9mm.Read that the trim to legnth is .751 and the max is .754. So I begin to measure my once fired brass ( I know many people that don't even bother measuring, they just clean and run it thru)and EVERY single one of them is below the trim to length and measure in around .745 and after resizing stretches out to around .748. All this is below trim to length.

My questions are as follows,

1- does this mean that all this brass must be chucked?

2- Is it unsafe to use brass slightly below the TTL and how will it effect the headspace and what happens with poor headspacing? Does too much pressure build?

3-If it's okay to go below trim to length how low is safe?
 
I'm not trimming my brass, I just started measuring my once fired brass due to the warning about case length in the manual.
 
My bad, I only read half of your post. I wouldn't be worried about your brass being that far off. Set your caliper for the .003 you are off and take a look, It's nothing to fret about :).
 
That pistol cases headspace off the case mouth is nearly a myth. In most relatively loose commercial chambers, the case headspaces off the mouth, the extractor, and depending on the bullet shape, the ogive.

Unlike bottle neck rifle cases, pistol cases shrink and fatten up ahead of the extractor groove.
 
I had this same problem with my rifle brass and am wondering about it as I am gettin into 9mm reloading.

If the headspace of the mouth is a myth, does that make it okay to shoot with undersized brass? Is the solution to seat the bullet slight longer?
 
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