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Timming Tech Question?


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#1 RobertR

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Posted 05 May 2010 - 07:07 PM

I would like to upgrade my trimmer but I have some questions about what is best way to gage the length.
Should the case be indexed off the shoulder for trim length?
Should the length be gaged the bottom of the case?
Should you use the flash hole as a Lee trimmer does to gage the trim length.
What is the correct and most accurate method.
I know there is a lot of variables in case styles, neck sizing versus full length sizing but there seems to be no set industry standard. I know what works for me but I want some answers as to why one is better that the other.
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#2 silvertip-co

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Posted 05 May 2010 - 08:00 PM

I dont know the why of anything, nor do I like to argue about it at this late stage of the game. But I trim to the min case length that my reloading manual(s) recommend. Occasionally I'll add a thou or two to make the case a lil longer for whatever reason. Case length is always measured from the rear face of the case
(as far I know). I would NEVER rely on a primer pocket to determine case length.

The choice to neck size or full length resize is personal too and is sort of depending on the calibre. In 40 yrs of reloading I have NEVER had good luck neck sizing. So I full lenght resize everything and if I dont get t he life out of the cases the ' media experts' say then so be it. SOme friends back east never full length size anything. So be it. Good luck reloading, it's a lot of high tech fun.

Edited by silvertip-co, 05 May 2010 - 08:01 PM.

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#3 Leo

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Posted 05 May 2010 - 09:29 PM

The overall length of the brass measured from base to neck opening is the critical measurement. Flash hole depth varies some and you are best to trim to minimum length when using a flash hole trimmer.

Brass that is too long can cause SERIOUS pressure spikes. Brass that is shorter than it needs to be has a shorter neck and costs you accuracy.

I use a chamber case length guage to determine the length of my chamber.

Sinclair makes the one I use.

Sinclair Chamber Length Guage

You have to use this guage plus a piece of your brass prepared per the instructions. You then measure the case and guage assembly (with calipers) and you trim to 0.024" less than that measurement. DO NOT TRIM THE BRASS TO THE EXACT LENGTH OF THE CHAMBER! That is too long and not safe.

Probably more than you wanted to know about trimming but in my experience it does help accuracy and increase brass life by minimizing stretch.

One more note: If you trim to this max size you need to trim after every firing. ;)
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#4 RobertR

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Posted 06 May 2010 - 06:44 PM

Leo that's kind of ironic because I have been looking at the very same thing you mentioned from Sinclair. I have Sinclair's catalog and they have a lot of neet products that are must hav's.
I just thought there might be an industry standard for a right or wrong method of trimming a case.
One of my better reloading books gives both a cut length and a trim length so I know what to set my trimmer length for trimming.
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#5 PA RIDGE RUNNER

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Posted 07 May 2010 - 06:19 PM

I do not have the sinclair system. All the books I have have a max case length and a trim to length. There is generally a 10 thousandths difference between max and min case length. As always Leo has posted an excellent reply. Case length is indeed measured from the bottom or head of the case to the end of the neck or mouth of the case. I have a specific step where I measure my cases and that is just before I am ready to prime a cleaned and resized case or just after priming and just before putting in the powder. You most certainly want to measure after resizing. I use a set of either dial or electronic calipers to do the measuring. I set my calipers to the max case length and measure all the cases. If even one is at or near the max length I trim them all. I use an L. E. Wilson case trimmer. This trimmer does not use a collet to support the neck of the case instead you must have a sleeve that has the inside formed for the caliber but lets some of the neck exposed the case with the sleeve is layed on a bed in the trimmer and you turn the handle like most hand case trimmers to shorten the case to the proper length. Certain cartridges you may have to trim each time you reload them such as those that require crimping and certain calibers such as the 270. Also eny time you trim a case you must chamfer the mouth inside and out. In this case you must have all the cases the same length or your crimp will vary.

As for full length vs neck sizing I most always only neck size. But then again nearly all my rifles are bolt action. In a lever action or semi auto you must always full length resize to get reliable chambering. In the bench rest world very few if any at all full length resize. The reason for that is once a cartridge is fired through a certain chamber it is form fitted to that chamber. If it extracts from the chamber easily it will reenter that chamber just as easily. Before I go hunting I always chamber each round I am taking to be sure of no problems. Some chambers are so tight that you may need a special resizing die called a small base die to return a fired case to factory specs. Full length resizing dies do not return a fired case to factory size but do reduce the overall size to allow them to work in nearly all actions.

Edited by PA RIDGE RUNNER, 07 May 2010 - 06:21 PM.

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#6 Tirador

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Posted 23 May 2010 - 07:46 PM

If you go to the trouble to neck size only, should you mark the breech and all of the cases on the rear face of the case, then line up the marks every time to insure the same case fire forming and close to exact cup pressure?

#7 PA RIDGE RUNNER

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Posted 23 May 2010 - 08:13 PM

Believe it or not some bench rest shooters will mark the breech and the case to line up the case in the chamber. I do not go that far but do have a certain color mark on cases that I have more than one rifle for so they stay with the same rifle.
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#8 Tirador

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Posted 29 May 2010 - 09:00 PM

Believe it or not some bench rest shooters will mark the breech and the case to line up the case in the chamber. I do not go that far but do have a certain color mark on cases that I have more than one rifle for so they stay with the same rifle.



on necksizing only-Is there a reason I cannot find neck sizing dies for my .300 Weatherby?i would like to get the most out of the expensive Norma brass.

#9 PA RIDGE RUNNER

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Posted 30 May 2010 - 07:45 AM

Neck sizing can be done in a full length die. Full length resizing in all dies, especially for tapered cases, is accomplished in the very last part of the stroke of the press. I most times will take a thin washer and place it under the full length die when inserting it into the press to not allow the case to be fully inserted into the die. This will allow the neck to be resized down to within the thickness of the washer of the neck. I have found this to be quite enough to grip the bullet adequately and gives me very good accuracy. I would also run each case through the action before going hunting to be sure they all work easily.
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#10 Leo

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Posted 30 May 2010 - 08:41 AM

PA Ridge Runner is right. Just back off a full length sizing die slightly and then you are neck sizing.

I reload for the 300WBY myself. What I do is neck size by backing off the full length sizing die slightly and THEN using Innovative Technologies belted magnum collet resizing die by Larry Willis. The Larry Willis die will fix brass that won't chamber after a full length resizing. I had almost 150 pieces of 300WBY brass that would not chamber until I used the Willis die. It's not cheap but the die practically has paid for itself in recovered brass!

It's important you resize before using the Willis die. I have seen an accuracy improvement in using this and the Lee Factory crimp die.

Get one here! I highly recommend this product for 300WBY users.

LarryWillis.com
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#11 REDGREEN

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Posted 30 May 2010 - 12:29 PM

RCBS makes a 300 Weatherby neck sizer die. As to the trimming, I trim 5 thousands below max.I also neck size only. I can't recall the last time that I had to use the full length dies. I also keep a fired trimmed case in each of my die boxes to set up my trimmer for whatever caliber that needs trimming. It saves me a lot of time and aggravation. I never had any faith in using a full length die for partial sizing. I tried it once, and not one of the cases would chamber comfortably. It was a job creation, because then I had to full length resize the whole batch, and refire form them all. OAL is definately measured from the head to the mouth of the case.




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