When to trim

Jim R

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Oct 16, 2001
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If your minimum chamber length/base to case mouth is 2.502, when should I trim back? Is there a rule of thumb for when to trim? Thanks in advance, Jim R
 

devildoc

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Feb 10, 2006
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Pueblo, CO
My personal rule of thumb is, if any of my cases are over max length, I trim all the cases I'm fixin' to reload. Also, If I'm showing a wide varience in case lengths I'll trim em' all. If you're loading for accuracy You want all your necks to be very close in length to keep your neck tension consistant, having necks that are very close in length helps with that. Hope that helps.
 

jmden

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If your minimum chamber length/base to case mouth is 2.502, when should I trim back? Is there a rule of thumb for when to trim? Thanks in advance, Jim R
Hi Jim,

I'm not sure what you mean by 'minimum chamber length'. Is this a SAAMI spec number? Do you mean SAAMI max case length?

Have you measured your actual chamber length? Sinclair Int'l makes a cheap and easy to use gadget to do this at: Welcome to Sinclair International's Online Store

Sinclair's book talks about actually measuring your chamber length using the above tool and then using that as a gauge to determine your trim length--a length particular to your chamber instead of a number in a book that may be causing you to trim much more than needed. If I recall correctly, they did some studies and looked at various publications and arrived at a number of .021 less than your chamber length as a max case length. In general, I believe they were talking about BR rounds. Knowing this you can adjust your trim length to fit your needs. I've been using this number with a 300RUM for several years and it's allowed me to keep a bit longer neck than I would've otherwise and not trim quite as often Good luck.
 

Jim R

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East TN
My exact max case length is 2.502 as provided by my gunsmith and confirmed by the Sinclair case length gauge (wonderful piece of equipment). After 4 or 5 firings from my 6.5-06, they are approaching the 2.470-2.480 range. This is a custom gun with all the measurments in hand so I am not real concerned about SAAMI. Thanks, Jim R
 

jmden

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My exact max case length is 2.502 as provided by my gunsmith and confirmed by the Sinclair case length gauge (wonderful piece of equipment). After 4 or 5 firings from my 6.5-06, they are approaching the 2.470-2.480 range. This is a custom gun with all the measurments in hand so I am not real concerned about SAAMI. Thanks, Jim R

OK, you didn't state what cartridge you were shooting or that the gun was custom initially. SAAMI's not so important--never was if you know your particular chamber length.

So, you used a Sinclair 'chamber length gauge' (not a 'case length gauge') to check your actual chamber length (not max case length) against the number your 'smith gave you (2.502), correct? (The correct terminology is (being on the same page) is very important in this particular discussion.)

If you can reply affirmatively to the above statement, my experience with a 300RUM at top loads is that I don't trim until I'm within .015 or so of my max chamber length as found by using the Sinclair Chamber Length Gauge. Just my experience. I'm no expert, but I'd say you've got another firing or two in those cases before trimming. Just keep on eye on them and check how much they are stretching after each firing. You may find that with milder loads, they stop stretching and you may not need to trim for a very long time. But, personnally, I problaby wouldn't let them go past 2.490. JMHO. Good luck and have fun shooting!
 
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Brain

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Jan 18, 2007
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VA
I also use the Sinclair Chamber Length Gauge for all of my rifles. Each rifle has a data book where I write down max length, trim length, jam-length OAL, etc...

When I am loading, I reference that particular rifle's book and trim specifically for that max length minus .025. Only when a case is longer than that value will I trim, but all cases are trimmed to the same length. Shorter cases than that value aren't used for accuracy loads.
 

Jim R

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Oct 16, 2001
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East TN
I suppose I was trying to be too simple with my question and was not clear. Seems like so many question posed on forums goes on and on and on with info.........

I used the term "min.chamber length/base to case mouth" because that is how it is referred to in the narrative provided with the work. This is the way Clymer Tool refers to this measurement.

It sounds to me there is no rule of thumb for when to trim except to say when it gets too close. The "how close is too close" part was what I was looking for.

Not looking for BR accuracy, but then again, maybe I am! Thanks for the replies, Jim R
 

Winchester 69

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I suppose I was trying to be too simple with my question and was not clear. Seems like so many questions posed on forums go on and on and on with info.........

I used the term "min.chamber length/base to case mouth" because that is how it is referred to in the narrative provided with the work. This is the way Clymer Tool refers to this measurement.

It sounds to me there is no rule of thumb for when to trim except to say when it gets too close. The "how close is too close" part was what I was looking for.

Not looking for BR accuracy, but then again, maybe I am! Thanks for the replies, Jim R
The forum has trashed my two attempts (on two separate occasions) to comprehensively answer your question, so forgive my brevity.

Zediker says 0.020 is a practical figure, ie, 2.482 would be the point at which to trim back.
 
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Jim R

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Oct 16, 2001
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East TN
Thanks for that. I felt like I was still in a good range, but thought I would see what others used. I was vague with the question and for that, I apologize. Sometimes my mind works quicker than my fingers......Thanks again, Jim R
 

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