Trimming brass


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TX1911fan
August 14, 2013, 12:40 PM
I've been reloading for a while now, but mostly pistol ammo and .223 for the AR, so I haven't been super concerned about all the tiny details. However, I want to start loading as accurate a .308 WIN load as I can. So, I've bought a case trimmer. I assumed that my shot brass would be longer than the specifications in the reloading manual, but when I measured, it was not. All of it is shorter. Do I only need to trim it when it gets too long? Or, in order to have the most accurate loads, do I need to pick a length and trim all my cases to the same length, even if that length is shorter than the spec length from the book.

Hope this makes sense. Thanks for the help.

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X-Rap
August 14, 2013, 12:55 PM
I believe you have two questions that need answering.
First, you will eventually need to trim your 223 brass if you wish to continue shooting it, eventually it all extrudes to the front to the extent that it won't chamber in your gun.
Second, if you want to maximize your accuracy potential I would start with a common lot of brass and from that point on treat it all the same as to how many times it is shot and cycled through your press and also keep it trimmed to the same specified length.
You can go further with neck turning and flash hole uniformity with mixed results but I think starting and keeping a matched set of brass is a good place to start.

IMtheNRA
August 14, 2013, 02:27 PM
Keep in mind that your brass will grow longer after you resize it, not after you shoot it.

Walkalong
August 14, 2013, 02:42 PM
Trim after sizing. Trim it all to the exact same length. Exactly what length is not as important as long as it isn't over the max your chamber can handle.

X-Rap
August 14, 2013, 03:05 PM
Trim after sizing is not always possible, If you use a progressive without a spare stage for a trimmer you will have to go by a measurement that you determine will give you a length that will go under the maximum for your chamber.

AABEN
August 14, 2013, 03:42 PM
Jest do NOT trim it shorter than what book call for. I use a Lee's trimmers for all of my brass.

TX1911fan
August 14, 2013, 03:49 PM
Thanks everyone for the excellent responses.

1. I will keep an eye on my .223 brass as I shoot it more to ensure it does not get too long.

2. I will trim after resizing. I'm only neck resizing as all the brass has been fired from my gun.

3. I wil make sure it is all the same length, but not shorter than the specs call for.

gamestalker
August 14, 2013, 08:35 PM
First of all, bottle neck brass must be maintained to within SAAMI maximum. Bad things can happen when brass exceeds it's SAAMI max, such as excessive pressure spikes, with the potential to cause catastrophic events. When brass exceeds SAAMI max it can cause the mouth to get pinched between the bullet and the throat, which is what causes pressure spikes.

Second, are you measuring your brass before or after resizing it? Brass is measured only after it has been re-sized, as that is when it is it's longest.

And third, yes, keeping your brass the same lengths can improve accuracy, as that helps maintain a more consistent pressure curve.

GS

Walkalong
August 14, 2013, 08:42 PM
Trim after sizing is not always possible, If you use a progressive I size all my brass on my LNL, then I tumble it, trim it, chamfer and deburr it, prime it, and then run it through the LNL again to load it. If you are not willing to do that, then don't have the space for a power trimmer on your press, then you will have to trim prior to sizing, but it will not be as precise.

dmazur
August 15, 2013, 06:05 AM
...I'm only neck resizing as all the brass has been fired from my gun.

This is the protocol for bolt-action rifles.

For semiauto gas-operated rifles (like the AR, Garand, etc.), full length resizing is the standard, to guarantee proper chambering without resistance.

Failure to chamber completely can result in slamfires...

medalguy
August 15, 2013, 01:35 PM
I'm with Walkalong. I load a lot of 5.56 and .308 military brass and I also size and trim with a Dillon 1200 powered trimmer. Only then do I clean it and start the reloading process. I believe it's entirely possible to get an errant piece of brass that's way too long and load it over max length unless you do this. The results can, of course, be catastrophic.

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