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need to trim new brass???

 
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  #8  
Old 06-15-2013, 10:45 AM
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Re: need to trim new brass???

I agree with Kevin and Mark. I trim after fireforming and re-chamfer.
My trim length is 5-10thou under chamber end(not SAAMI), but if you're running a cartridge that's expected to grow with reloading cycles, and you don't have a gracey on the bench, you can trim more off.
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  #9  
Old 06-15-2013, 01:38 PM
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Re: need to trim new brass???

DMAX1800,
You may want to check the Math on the difference on the brass measurements.
Have a great day.
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  #10  
Old 06-15-2013, 02:32 PM
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Re: need to trim new brass???

Quote:
Originally Posted by 25.06 View Post
DMAX1800,
You may want to check the Math on the difference on the brass measurements.
Have a great day.
Looks like there is an accidental "0" in there. Otherwise he has a bigger problem than trimming. But, being able to measure to hundred-thousandths would be cool.
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  #11  
Old 06-15-2013, 11:20 PM
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Re: need to trim new brass???

Quote:
Originally Posted by MontanaRifleman View Post
I have never found any significant accuracy issue with necks that are not exactly the same length. New brass is usually shorter than spec and some more than others. My practice is not to trim to length until after the first firing and sizing.

You have about 6 thou of variance. Take your calipers and open them to 6 thou to see what it is.
I agree neck length is not as important as neck squareness . However it's one of those minor case prep jobs that is hard to prove that it helps all by its self .
I find it helps bullets seat straight and bushings size straighter .
Start with a square well chamfered neck is basic in my system .
Most factory chambers are around .015 to .020 longer in the neck area than factory brass anyway .
I don't trim to an actual length it's irrelevant to headspace , seating depth or OAL . I trim to slightly shorter than the length of the shortest case in a batch so they all come out square and the SAME length . When you seat a bullet you set the OAL or seating depth whichever you are working with , either magazine length or ogive distance from the lands .
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  #12  
Old 06-16-2013, 02:32 PM
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Re: need to trim new brass???

Quote:
Originally Posted by Bullet bumper View Post
I agree neck length is not as important as neck squareness . However it's one of those minor case prep jobs that is hard to prove that it helps all by its self .
I find it helps bullets seat straight and bushings size straighter .
Start with a square well chamfered neck is basic in my system .
Most factory chambers are around .015 to .020 longer in the neck area than factory brass anyway .
I don't trim to an actual length it's irrelevant to headspace , seating depth or OAL . I trim to slightly shorter than the length of the shortest case in a batch so they all come out square and the SAME length . When you seat a bullet you set the OAL or seating depth whichever you are working with , either magazine length or ogive distance from the lands .
Some valid points for trimming before firing. I figure shooting unfired brass typically gives slightly different results anyway, especially if you neck size only (I don't) and I have not seen significant differences in results by not trimming until after the first firing. I like my necks to be as long as possible for a few reasons and I figure waiting until after the first firing accommodates that, especially with sharper shouldered cases that don't much if at all.
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  #13  
Old 06-16-2013, 03:35 PM
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Re: need to trim new brass???

Here's something to consider? Someone or some machine cut the chamber, and not every chamber is cut to an exact perfect measurement each and every time! The person doing the reamer work might not have held to the measurement stated by the published (SAAMI) maximum chamber length!

I always measure the chamber before resorting to trimming to the published trim lengths by using a Sinclair Chamber Length Gage. It's a simple item that is seated into a fired case that the neck is cut way back and chambered. I have found rarely are they cut to the published trim lengths! Most notable what I have found is that they are cut longer then the published maximum trim lengths, onetime grossly too long that timing would have never become necessary! This instance was a barrel chamber cut by Shilen Rifles while using a body reamer and a different piloted neck reamer that opened up to the proper neck to size of the case. Had I not measured the case length I would have been trimming way beyond the actual chamber length and in this case a charred area would have developed between the point where the case mouth stopped (trimmed neck), and the where the chamber actually ended! I actually sent back that barrel because of that mistake made, and unfortunately my 25" barrel is now 24 1/2" inches but the chamber was cut closer to maximum but still very long!

When I mean too long, the chamber actually measured 2.1585" inches long, which is 0.0585" longer then the published length of a case, and 0.0685" longer then the trim to length. After is was cut a second time, it measured 2.1445" when it should have been cut to something like 2.11-2.1150" which is what the reamer Company had them set up for, but the person doing the cutting needs to pay attention to the depth of the cut for that measurement to be produced.

For an actual measurement to find your individual rifle(s) chamber length to trim to, I'd invest in the six bucks for the Sinclair Chamber Length Gage. It's cheap and very easy to use, otherwise you just might not be trimming your case necks to the proper length? Which could be longer or shorter the the published trim length your cutting them to?

Why over trim a case when you have no idea how long the chamber actually is. On another note, it would be worse to have the chamber cut too short which is why they tend to be cut so long.
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  #14  
Old 06-16-2013, 06:54 PM
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Re: need to trim new brass???

It's always stunned me to hear a reloader concerned with numbers in a book, while holding the actual items in-hand to simply measure..
How blind does it get?
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