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need to trim new brass???

 
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  #1  
Old 06-14-2013, 09:49 AM
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need to trim new brass???

I am new to reloading. I've read that you need to measure everything and be absolutely consistent. I just got 100 Norma brass in 300 win mag. Just out of curiosity I measured the length of 10 randomly selected cases. They range from 2.06065 to 2.6120 inches in length. Is .0055 too much variance in new brass? Should I trim the new cases to get them exactly the same length before firing them for the first time? Will the variance in length effect accuracy is my biggest question. I know that you should trim the cases during the reloading process after they have been fired. I have the inserts to measure the chamber length.

Thanks.

Last edited by dmax1800; 06-14-2013 at 09:50 AM. Reason: fix typo
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  #2  
Old 06-14-2013, 10:00 AM
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Re: need to trim new brass???

dmax,

Trimming is a safety measure, and is required to ensure the case mouths don't encroach on the throat too much. The cases will tend to stretch a bit as they go through the firing/reloading cycles. Some calibers are worse about this than others, the intensity of the load as well as the way in which it was resized, and a host of other factors come into this as well. But new brass, right out of the box, should never need to be trimmed or sized. The variation you're seeing there won't be a problem at all.

We (Lapua) do recommend running new brass over an expander mandrel before the first loading, just to uniform neck tension and round out case mouths that may have been dinged or knocked out of round during shipment. Not really a reloading step per se, but just a little due diligence to make sure everything's "right" on that first go-round.
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  #3  
Old 06-14-2013, 10:07 AM
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Re: need to trim new brass???

Load, shoot then trim.I try to not remove any more brass that it takes.Use the short ones as sighters or foulers,,,they will get longer.
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  #4  
Old 06-14-2013, 06:16 PM
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Re: need to trim new brass???

I generally trim new brass to trim-to length for two reasons:

1. I get an equal index point to deburr the flash holes.

2. I can measure my work-up loads to see if any combinations exhibit relatively high or low stretch after firing.

Normally I don't resort to name calling, but if you follow my advice regarding brass over Kevin's you are dumb.
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  #5  
Old 06-14-2013, 07:37 PM
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Re: need to trim new brass???

Quote:
Originally Posted by Kevin Thomas View Post
dmax,

Trimming is a safety measure, and is required to ensure the case mouths don't encroach on the throat too much. The cases will tend to stretch a bit as they go through the firing/reloading cycles. Some calibers are worse about this than others, the intensity of the load as well as the way in which it was resized, and a host of other factors come into this as well. But new brass, right out of the box, should never need to be trimmed or sized. The variation you're seeing there won't be a problem at all.

We (Lapua) do recommend running new brass over an expander mandrel before the first loading, just to uniform neck tension and round out case mouths that may have been dinged or knocked out of round during shipment. Not really a reloading step per se, but just a little due diligence to make sure everything's "right" on that first go-round.
You might be from Lapua but I disagree with one thing . New brass is not always square at the mouth and triming to square it up is a good idea as a square case mouth helps accuracy . Also squaring up the mouth and correct chamfering helps neck sizing and bullet seating .
Also some minimum spec chambers will actually need some factory brass to be sized down slightly just to get them in . Never say never .
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  #6  
Old 06-14-2013, 08:14 PM
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Re: need to trim new brass???

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.
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  #7  
Old 06-15-2013, 04:41 AM
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Re: need to trim new brass???

Trim about 005" - 010" below SAMMI length. Check again after first firing. Don't forget to champfer case mouths.
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