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Don Fischer's picture
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I'm not suprised. Most magnum chambers are a bit sloppy. When I loaded magnums, I always got that expansion ring in front of the belt before I ever had to resize. I think that had I partial resized back then, I could have increased the case life but would have had to trim now and again. By partial resizing you change the relationship of the shoulder of the case to the chamber. That reduces streach in the belt area when it's fired increacing case life. I have to admit that in my magnums, being conservative was not in me. My favorite load in an old L61R Sako was with the 160gr Speer and a charge of old N205 that was 4grs over max. I'd had it long throated prior to developing that load.

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I always trimmed the brass because the book said to. The other day while reading through the Lee Reloading Book, the issue of case trimming was discussed. According to my book, excess case length can affect the "hardness" of the crimp and the chamber pressure.

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haiku_rodney wrote:
I always trimmed the brass because the book said to. The other day while reading through the Lee Reloading Book, the issue of case trimming was discussed. According to my book, excess case length can affect the "hardness" of the crimp and the chamber pressure.

I am like you. I follow the book. Also, I figure it is good to have uniform size cases. Might not matter, but it doesn't take me long to trim them up to trim to size and have them all nice and uniform.

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The thing is to be consistant. Pressures will vary because of bullet seating depths(distance from land/groves) more so than trimming, unless you unwisely venture below or above the minimum <> maximum case lengths. Trimming cases to a precise measurement every time will be more paramount when reloading for semi auto, some a way more fussy than others.
I don't know if having a couple of reloads not trimmed the same as the others in the pile will make any difference noticeable at the range or not(seating depths the same)...can't remember every trying it, but I bet the Ol Guy from Oregon has Yes
So what's the scoop, Don ?

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Quote:
Pressures will vary because of bullet seating depths(distance from land/groves)

You raise an interesting point. I noticed a variation in bullet length - anywhere from .002 - .005 inch. Is this significant?

If you seat them all to be the same length how does that affect things (some will be seated deeper) or if you seat them all the same depth some will be longer. Is that length difference enough to matter?

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Once you trim then, they are all th same length. But for some reason the streach different. I have never noticd that the little difference made much difference. On the 243 the difference between max and min length is .010". that ain't very much. Where the problem starts is when you exceed max length and the lands don't aallow the mouth to open right and let the bullet out. Thats when the pressure starts to jump.

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