Importance of case trimmed length
- Thread starter NICKNICK
- Start date
The major issue with letting case necks get too long for a chamber is that the neck will be forced into the lands which in turn will crunch down on your bullet and change your neck tension. In a worst case scenario the extra tension causes an over pressure situation and all hell breaks loose on your face. You can buy a gauge from Sinclair that will allow you to measure how long you can run your neck length out before you need to actually trim back to the minimum specs.
In an extreme case, that makes sense. Thanks for the reply.
I don't think I'll run into problems with jamming the case into the lands--I'm reloading once-fired FGMM brass for use in a factory barrel. I'm low on time, so I was looking to shortcut the reloading process. I've always trimmed cases, but I figured I could get away with it just this once. As long as it doesn't affect accuracy, I'm happy.
I don't think I'll run into problems with jamming the case into the lands--I'm reloading once-fired FGMM brass for use in a factory barrel. I'm low on time, so I was looking to shortcut the reloading process. I've always trimmed cases, but I figured I could get away with it just this once. As long as it doesn't affect accuracy, I'm happy.
You should at least take a measurement on random pieces of brass to check the length. I've found that once-fired .308 FGMM brass is on the long side....typically around 2.010". They even grow a little more once you full-length size them.....in other words, full-length size them and then take a measurement.
After you size the brass take the measurement and I trim when the brass gets to 2.015 (SAMMI SPECS)
I've purchased a ton of FGMM once-fired brass....from a factory gun. It was way past 2.015. If I didn't trim down, they would get stuck in my gap10. no bueno.
Better yet is to measure the neck length in your chamber, and simply keep your brass shorter than that number by at least .005".
Of the 3 or 4 factory 308s with SAAMI chambers I've measured, all would accomodate brass 2.045".
So i do not mean to steal this thread but i also have a question. Given all the case lengths are in spec (min/max) what effect on accuracy would a varying case length of say .010-.020 have??? Do you trim every reloading or do you trim every other??? Or what? I have always trimmed every time do to the varying lengths i have recorded after firing and sizing.
I always trim after every time I size to ensure consistency. When the necks get longer or shorter, neck tension is affected. Which affects pressure, which affects velocity, which affects accuracy. Depends on what your goal is when you hand load....some only trim when it reaches the max length and some do what I choose to do.
Turbo, forgive my ignorance here, but could you enlighten me on how to measure the neck length of the chamber? I am not sure how to go about that, but would like to do so for my rifles. I was wondering about it and then came across this thread.
Thanks
No problem man. Those gauges are are handy for sure if you want to let necks get as long as possible.
After full-length resizing the brass was between 2.015 and 2.017. I haven't tried the rounds yet, so no word on accuracy or function, but I'm betting they at least won't get stuck in a factory-throated bolt gun.
In the end, not trimming was a mistake. The case mouths were sharp enough to shave the jackets on the first couple of bullets, so I ended up chamfering the inside. Unfortunately a bunch of the cases already had their powder charge, so I had to empty them, set the powder aside, reconfirm the powder charge on the balance to make sure none got left behind in the case, chamfer, put powder in again...etc. In the end, it took me just as long to load as if I hadn't taken the shortcut. I spent the same amount of time, but now I have a batch of ammo with an unnecessary variable.
oh well. live and learn.
