Case Trim Length

[PALefty]

I am in the process of preparing my first reloading cases this weekend. In doing so, I plan on following the following article: http://www.6mmbr.com/jgcaseprep.html

At this point in time, I am only reloading for hunting purposes. I purchased a number of measurement tools to try and find out how my chamber differs from published SAAMI dimensions. I would prefer to trim the overall length based on my chamber rather than the more generous SAAMI. What tool/tools are used to ensure that I am using an accurate number?

thanks,

Jeff

 

[billmo]

Jeff, Sinclair Intl. sells a tool called a chamber length measuring tool. I personally have not used one but Sinclair says
this will accomplish your goal. The # is 800 717-8211. I hope this helps. Bill

 

[Cheechako]

Jeff

Take a case with moderate to light neck tension and seat a bullet it in backwards. Flat base bullet, that is. Chamber it. Remove and measure. If your chamber is close to case length you may want to sacrafice one case and trim it back .050" or so before you start. That will be your gauge so it's not completely lost.

Ray

 

[Ackman]

Lots of people waste a lot of time trimming fresh brass unecessarily because they think it's the thing to do and that it'll help accuracy. You may wind up with cases that are all the same length, but you won't see the slightest difference in the way they shoot. Trimming brass won't make it fit a SAAMI chamber either. The only way to do that is make it longer. With a Sinclair chamber length gauge you can tell just how long the chamber really is, and it'll be considerably longer than the case. Like about .020", maybe even .030". For a hunting gun with SAAMI chamber, you should never have to trim cases.

 

[PALefty]

Thanks for the replies!

I did purchase one of these from Sinclair... so I am glad to hear that it is what I need! I didn't know that I could perform the same test with a backwards bullet.. though it makes sense. I will keep this in mind if I need to measure any other chambers in the future. I agree,from what I have read) that it may not be necessary to trim the cases for a factory barrel.. which is exactly the thing I want to avoid by getting this measurement.

In reading the instructions for the Chamber Length Gauge.. it states to use a full length sized case,cut back .1) to make my measurement. Obviously the fl sizing would put it to SAAMI specs. Wouldn't it be better to use a previously fired case for this? I would think a fired case that has been formed to my chamber would be a better indicator... unless I was trying to get a measurement relative to SAAMI specs. Am I off base in this line of thought?

 

[janderson0]

Be careful playing with chamber length measuring. Get it wrong, and you will increase pressure REAL fast.

My understanding is the cut from neck to throat is a 45 degree cut. Depending on the throat size the upside down bullet in a case will measure the lands not the end of the neck. The home made tool I've seen is to cut a case in the mid neck, then put this "ring" on a bullet slipped into the other part of the cut case. Then you are using the correct dia.,the neck) not a bullet.

Jim

 

[chino1969]

Jeff, Sinclair Intl. sells a tool called a chamber length measuring tool. I personally have not used one but Sinclair says
this will accomplish your goal. The # is 800 717-8211. I hope this helps. Bill

Jeff,
I've used the Sinclair tool and it's only about $7, comes with easy to follow instructions, and will measure your true chamber length. It's made from leaded steel and will not damage your bore. Call Sinclair; they'll know exactly what you are talking about.
Chino69

 

[Cheechako]

Jeff

Jim is right. I made a mistake. What I suggested will NOT measure the chamber length. It will measure the base to ogive. Please do it the right way. I apologize if I have steered you in the wrong direction.:,

Ray

 

[PALefty]

No problem.... as I received the chamber length gauge from Sinclair last night,among other things). I wanted to make sure this was the right tool for the job... as well as verify if I should use a previously fired/formed case or one that is full length sized. The instructions state FL sized.. but I would like to verify that this will be more accurate than the formed one. It seems to me that the formed one would be more accurate...?

 

[PALefty]

I just got off the phone with Sinclair.. and they were helpful. According to their CS, the two main conditions that need to be met are that it will chamber easily and that it will hold the gauge with the proper amount of tension. A spent cartridge may not chamber easily. If it does, you could use it.. but you will most likely have to neck size it in order to have enough tension... ie, it needs the same amount of tension as if you were seating a bullet. Ok, that makes sense to me.

fyi- He also said that it is only necessary to perform this test once and it is not necessary to do it many times and take the average. If you do it more than once, you can skip the instruction step of drilling the case if you have a hammer style,kinetic ?) bullet puller.

Thanks again for your suggestions. I imagine will have some more basic questions in the near future...

Jeff

 

[Raidman]

Palefty, if you used a fired case it would not hold the bullet tight enough to make the test. You have to trim .100 off the end of the case to make room for the rim on the slug that goes into the end of the FL sized casing. By seating the slug .100 longer than specs you can seat the slug with the bolt and it is held in place so you can measure the distance from the bolt face to the end of your chamber neck. After you get that measurement you know exactly where to trim your cases.