Trim to length

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Trim to length

Post by semtav » Wed Apr 14, 2021 3:33 pm

After reading this thread a couple times, I'm slightly confused.
Since all I've trimmed and shot for a long time is brass that is to be shot as fired
I trimmed to chamber length or just slightly under.

Now I always thought that is the length one should trim brass that is to be sized also.
Trim to chamber length, then resize winding up with a case slightly longer than chamber length.
With the understanding, that once fired, the case would instantly shorten as it expanded.
If one were to trim it to chamber length after sizing, it would be short of chamber length after firing leading to more possibility of paper rings.

Yet, that is not what Kirk or Ray alude to ?

Any Known pros-cons from doing it either way?

Coltsmoke alluded to shooting with cases longer than chamber before , and maybe that is what he is talking about !!

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Re: Trim to length

Post by TexasMac » Wed Apr 14, 2021 5:17 pm


Assuming I have the option such as when reforming .45-70 to .40-65, I trim the full-length resized case length to 0.015" longer than the chamber to allow for neck expansion & fireforming. Neck expanding a full-length resized case neck will typically shorten the case by 0.005", & fire forming will typically shorten it another 0.008" to 0.010" depending on loose or tight chamber dimensions. If I'm stretching brass the same applies but sometimes it's tough to obtain 0.015" over chamber length when starting out with new 2.090" or 2.095" brass for a .45-70 chamber for example.

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Re: Trim to length

Post by bpcr shooter » Wed Apr 14, 2021 6:12 pm

One thing that is talked about is "rim thickness" I have always used Starline brass and believe it is of very good quality. After I switched to DDPP loads I was shooting way better but wanted more..... I wanted to wring out all the accuracy I could, so I started looking at my components and how I could make them better, I found the rim thickness does vary and when measured from where it seats in the chamber to the case was short. After going thru 600+ cases (not real fun by the way) I separated them like some do when they weigh bullets, I resized, shot and trimmed them so all were the same length, as to have the same amount of case in the chamber, accuracy improved overall. I do lightly anneal every time maybe 2-3sec. I havn't had to trim a case in quite a while now, but I did leave them .002-.003 short from the start. I still think I can find more in it with lead mix , and thats what this years plan is.

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Re: Trim to length

Post by bruce m » Wed Apr 14, 2021 8:02 pm

what you are doing with rim thickness consistency is amongst other things giving the bullet a consistent relation to the rifling.
this will help accuracy a lot.
with regards case length, sizing brass and running neck tension really complicates the issue.
fully fireformed brass using slip fit proper sized bullets gives the same case length before and after firing.
ventum est amicus meus

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