View Full Version : Precision Reloading and Case Length
I have a McMillan tactical rifle chambered in .308 that I will be reloading for. I have been saving my brass for years, but I am just getting started in reloading. I know that my brass is fire formed to my rifle's chamber. My reloaded rounds will be fired only in this rifle. I will only be neck sizing the brass. Because of this, do I still need to worry about case length?
I have a McMillan tactical rifle chambered in .308 that I will be reloading for. I have been saving my brass for years, but I am just getting started in reloading. I know that my brass is fire formed to my rifle's chamber. My reloaded rounds will be fired only in this rifle. I will only be neck sizing the brass. Because of this, do I still need to worry about case length?
I would. If the case length is longer than the maximum recommended specification, when a round is chambered the case mouth could be crimped a little tighter by the chamber just behind the free bore, which would cause a change in neck tension and point of impact. My Hornady reloading books warn there could be a problem with overpressure when loading close to or at maximum charge weights.
I neck size and trim the brass to the same length each time I load for precision shooting.
Measure spent cases, if stretched trim them to size.
Thanks guys. Its time to order a case trimmer.
I rarely address case length for precision bolt gun ammo. I picked up on this from one of the OG's on accurateshooter.com. This post will set the "by the book", beaten silly as a child for coloring outside the lines, gauge everything faggots' asses on fire. But if you have your sizing die set up right, you really don't have to be fanatical about case length. And I've NEVER found uniform case length to improve accuracy at all.
Keep in mind that this is unique to the weapon/chamber. If somehow you got a factory chamber that wasn't cut with a throat as deep as Mylee Cyrus's, you may not be able to be case length insensitive. I've never read of this happening in the real world however.
That said... for .308, I check every 3 or so firings and trim only the most obnoxiously long cases. 300WM, 7 mag, 338WM, etc... NEVER get trimmed.
If they get too long, you will need to trim them. How long is too long? Depends on your chamber. Usually the number in reloading books is a bit conservative. I have, however, had cases get too long and pressure goes through the roof.
Also don't plan to only neck size brass. That works good for a few firings, but eventually they will get hard to chamber. There is little to no advantage to neck-sizing for a gun that gets used away from the bench. I FL size my precision ammo, including that for my competition rig. I want the brass to easily chamber every time, even with a dirty chamber. I bump my shoulder back 0.003".
Do yourself a favor and get a FL die. If you can afford only one, get a FL die.
Also a good tip, don't mix different stamps of brass.
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I prefer to always know the numbers - gives me a warm & fuzzy to know exactly what the dimensions are - and once you know where you are - it makes it far easier to get to where you want to be.
With that said - I looked at a dozen reamers I have & their corresponding prints. This include SAAMI 308 Win & 762 NATO as well as all the popular match reamers that are derivatives of those parent cases.
The shortest 308 / 762 case was 308 Obermeyer Special at 2.018". The next were the Palma 95 Match & the Palma Match at 2.020". After that, all of them were at 2.025 to include the SAAMI 308 WIn & 762 NATO.
The books tell us to trim to 2.005". I agree with what others wrote in that this is far to conservative. If you are growing brass beyond 2.025 - there are some serious issues that need to be addressed. It is rare that brass grows that much if proven methods of reloading are adhered to.
1. Expander balls being pulled back up through excessively sized down necks are the first culprit.
2. Multiple firings and reloadings tend to produce brass flow into the neck area making the neck wall thicker and this leads to pressure issues with excessive neck tensions.
3. Tight neck chambers present a unique set of problems and benefits all unto their own.
A standard SAAMI 308 runs a neck diameter of .346 tapering to .344". 762 NATO runs basically the same. In the world of precision loading - thess are generous dimensions that should never cause you a problem. (diameter wise)
Uniformity is a great thing. Find your shortest case (within reason; i.e. 2.010") and trim everything to the same dimension. I'd keep all your brass below 2.020" and never trim to 2.005" It's a waste of time (and brass)
If all your brass varies and it is between 2.005 and 2.020" - leave it - shoot it and reload it to settle it and then uniform it.
Neck sizing is great in certain applications. However, many many high end shooters find some of their best scores have been shot with new FL sized brass. I too have seen this. The one thing you truly want to stay away from is an expander ball. If you FL, then get a FL die that uses neck bushings.
Bottom line - don't over work the brass.
Neck bushing dies work best with cases that are neck turned and have uniform neck thicknesses, with a bushing die and unturned necks all you do is push the neck irregularities to the inside of the neck
You can get good runout figures by full length resizing with minimum shoulder bump using the correct diameter expander ball that is properly centered in the die. Or else you can size in a two step process by full length resizing without the expander button and use a expander die on the necks that is pushing "down" on the case as the expander enters the neck.
The quality of your cases with uniform case and neck thickness have more to do with accuracy than your dies.
I bump my shoulder back 0.003".
I make no measurement of how much I bump. I go all art on that.... take 3 tight cases and set the die up so they all just chamber like heaven.
Do yourself a favor and get a FL die. If you can afford only one, get a FL die.
I agree. If you set up a FL sizing die just right, you simple run everything through, all the time and life is easy.
I honestly don't even use neck dozers anymore.
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Information is key.
Get this:
http://www.sinclairintl.com/reloading-equipment/measuring-tools/case-gauges-headspace-tools/sinclair-chamber-length-gage-prod32925.aspx
The gage will allow you no measure the length of the chamber. Once you know that you will have your maximum case length. This figure is often beyond the SAAMI max. length.
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