Minimum case length??

[Xshot]

I've been reloading for about a year and have learn much along the way. When I started reloading I purchased several thousand once fired Lake City and Winchester brass. If brass was more than .002 under recommended trim length, I threw it into a separate bucket and didn't reload it.

I'm now getting into my own premium once fired SSA, Winchester and Hornady brass. I'm finding about 10% of this brass either right at recommended trim length or a few thousandths under. I even have brand new Winchester brass that's falling into this category. Chamfering the case mouth will take another thousandth or 2 off.

So here's the question. If the case max lenght is 1.876" and recommended trim length is 1.776", what is the acceptable/safe minimum (i.e. loadable) case length?

I've looked for the information in my reloading books, but have not found anything on the subject.

 

[MitchAlsup]

Re: Minimum case length??

The issue, 95%-ile is having case necks too long. As long as the case in question has at least 1 caliber of neck length, it is long enough to hold the bullet safe and securely.

The issue with necks that are too long has to do with instantaneous growth during the firing cycle. If the neck grows far enough to run into the end of the throat of the chamber, then the brass will be deflected into the bullet, grab like you will not believe, and cause very bad pressure situations.

0.005-0.015 too short--don't sweat it.
0.016-0.025 too short--probably not a match case anymore, but as long as the neck remains at least on caliber long; its ok for plinking and foulers.

 

[Xshot]

Re: Minimum case length??

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: MitchAlsup</div><div class="ubbcode-body">The issue, 95%-ile is having case necks too long. As long as the case in question has at least 1 caliber of neck length, it is long enough to hold the bullet safe and securely.

The issue with necks that are too long has to do with instantaneous growth during the firing cycle. If the neck grows far enough to run into the end of the throat of the chamber, then the brass will be deflected into the bullet, grab like you will not believe, and cause very bad pressure situations.

0.005-0.015 too short--don't sweat it.
0.016-0.025 too short--probably not a match case anymore, but as long as the neck remains at least on caliber long; its ok for plinking and foulers. </div></div>

Mitch - thanks for the quick response. Is your first example "0.005-0.015 too short" referenced from the recommended trim length, or?

 

[bdh308]

Re: Minimum case length??

Xshot,

Another good way to remedy your situation is to find out what your throat length is. Take a piece of brass and cut the neck in half (preferably with a lathe but dremel or a fine tooth hack saw will work). Save the half you cut and seat a bullet into the cartridge keeping the bullet extra long. Now take the half you cut off and place just over the bullet. Go ahead and load it into your chamber and see how far that piece slides back on the bullet. Do this several times making several measurements with calipers and it is recommended you take the firing pin out of the bolt for ease of use.

Once youve found your throat length you can now allow your necks to grow based on your chamber dimensions. Trimming your brass to short can cause advanced throat deteration. Keeping your necks longer will save your throat in the long run.

 

[mdesign]

Re: Minimum case length??

The posted min, max and trim length for cases come from the SAMMI specs for that cartridge. Unfortunately, almost none of the brass being made today, perhaps with one or two exceptions, is as long or thick as it should be per the specs.

Are they doing it to save brass? Not sure.

The maximum case length is what your chamber will allow but in most cases you will have to shoot your brass a number of time to even get it close. You most likely will have to trim to a predetermined length along the way so at least your cases are consistent in length.

The easiest way to find the length of your chamber is to buy a chamber length gage from Sinclairs and follow the instructions on how to use it. I have found that most chambers are longer than SAMMI and if you trim to a published length, you are trimming way short and contributing to your carbon ring and throat wear problems.

Once I know the actual length of a chamber, I trim .007 shorter and check it every time I size the brass to see if it needs a touch up. Hot loads mostly will as they stretch brass more.