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Old March 11, 2013, 07:11 PM   #1
jlcrss
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Case trimming question

How necessary is it to trim my cases? I am reloading once fired hornady match brass. It's all measuring consistently 2.016. Can I get away with not trimming?
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Old March 11, 2013, 07:16 PM   #2
243winxb
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What cartridge? Trimming is a must for most bottle neck rifle cartridges. Maximum - .010" is common.
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Old March 11, 2013, 07:25 PM   #3
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Sorry, I am loading the 308win.
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Old March 11, 2013, 07:32 PM   #4
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Trim length

Rcbs says 2.015 is max length and should trim to 2.005
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Old March 11, 2013, 07:33 PM   #5
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Whats the problem if it isn't trimmed?
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Old March 11, 2013, 07:38 PM   #6
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Depending on how the chamber is cut the case can grow Longer than the chamber and when the bolt locks it can further "crimp" the brass into the bullet and increase chamber pressures. The brass should not be longer than the intended chamber
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Old March 11, 2013, 07:39 PM   #7
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Ok thanks. Good to know.
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Old March 11, 2013, 10:33 PM   #8
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overlength brass can extend beyond the chamer, into the barrel, where there is not enough room for the brass to expand and release the bullet. This means higher pressures, and can be dangerous.

A max length case should chamber and fire ok, BUT since there are tolerance differences between chambers, we trim the brass to ensure safety in all chambers.

New brass nearly always stretches (and stretches the most) on its first firing. It may not strech again for seveal firings, or it may stretch a bit each time. Your loads, and the fit of your chamber and sizing die are the major factors in this.
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Old March 12, 2013, 07:42 PM   #9
oryx
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Another good reason to always measure and trim is if you are seating and crimping bullets with a cannelure. This always insures that your dies contact the case mouth in the same position and it actually crimps into the cannelure. If your lengths are all over the place, you will not get consistent crimping and possibly change pressures

If you want to measure your chamber and see what it will actually allow for the max case length you can use a product called cerrosafe which is a low temp casting alloy. You can easily melt it and pour it into your chamber and let it harden. When you drive it out, you can actually use it to measure your actual chamber dimensions and observe the throat conditions. Lots of good info can be obtained for more advanced use.
Not suggesting it is necessary, however.
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Old March 13, 2013, 12:37 AM   #10
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Sounds like someone needs to read a reloading manual
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Old March 13, 2013, 05:59 PM   #11
Bart B.
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44Amp claims:
Quote:
New brass nearly always stretches (and stretches the most) on its first firing.
Every new case I've handloaded for .222 Rem. .243 Win., .270 Win., 7x57 Mauser, .308 Win., .30-06, 7.65x53 Mauser, 8x57 Mauser rounds has got shorter when first fired. Same for factory or arsenal ammo in most of those cartridges. Their bodies were larger after firing, so the brass to do that had to come from someplace. Betcha a dollar it got drawn back from the shoulder and neck of the new case.

They all got longer after being full length resized. Then when those reloaded cases were fired again, they all got shorter.

I don't think any case headspacing on its shoulder gets longer when fired. Even my 30 caliber belted cases full length sized to headspace on their shoulder get shorter when fired.
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Old March 13, 2013, 06:47 PM   #12
math teacher
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Interesting Bart. I have often had to trim once fired rifle cases. I guess it depends on what chamber we fire it in and how we load it.
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Old March 13, 2013, 07:14 PM   #13
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Math Teacher, did you measure those new cases' OAL before firing them?

If it's a rimless case, they'll sometimes get longer; their head's held against the back end of the chamber and their shoulder gets blown forward.

Same for new belted magnum cases; my 30 caliber ones sometimes did get a bit longer when fired.
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Old March 13, 2013, 08:57 PM   #14
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I would have to agree Bart. I mostly neck size and even though I trim after every sizing, the trimmer rarely does more than make a faint shiny spot.
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Old March 16, 2013, 12:29 PM   #15
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Trimmed cases uneven

Figured out how to start a new thread. Moved my question there.
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Old March 16, 2013, 12:38 PM   #16
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What counts is after re-size, not the after its been fired.

So, yes they are shorter after firing (at least in the ones I shoot), but once re-sized they are their shooting length and that what counts

If they are past the max allowed length then they should be trimmed back.

So, you check them after re-size step and then trim or not trim.

I don't get too carried away, if I trim and they are between the two lengths I don't keep triming. No matter where the trimmer is set, some trim down more than others so I just mike each one.

The one that avoids all that is the Gerrard and I wish I could afford one (my brother has one and we do large numbers of 223 and I just stash it). If I get enough 30-06 I can do the same thing.
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Old March 16, 2013, 01:03 PM   #17
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I can trim them in roughly the same amount of time I can measure them, so I just trim. I usually buy my brass by the 100 and put it all back in the same box as I fire it. Process it all at one time, and every time I go through the box it gets another black line on the inside top lid. Amazingly, there always seems to be a few that do not trim at all and a few that get a lot taken off them when I go through the 10 or 98 or whatever is left.
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Old March 16, 2013, 01:08 PM   #18
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Quote:
The one that avoids all that is the Gerrard...
Yes, the Giraud provides a consistent trim length based on the shoulder position. So, if your resizing process is consistent, case length will also be consistent.

Something to note, however, is that if there is some variation in "shoulder bump", the Giraud will only trim based on the shoulder, so variation in case length will be evident after trimming.

It really is two separate things to chase -

Control resizing so "cartridge headspace" (head to shoulder) is consistent.
Control trimming so shoulder to mouth is within safe limits.
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Old March 16, 2013, 05:19 PM   #19
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I bought a series of plugs from Sinclair International that allows you to get the exact maximum case length. You shorten a resized case until only half the neck is left then slip in the proper cal. plug, then carefully insert it into the chamber, remove & measure. Then you have the max case length for your rifle.

Also, I've never tried them, but RCBS makes a resizing die that controls case length so no trimming is required. Don't know how that works(?)
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