308 neck sizing in an AR

H

hammer58

New member
I am looking for some great answers and wisdom from all of you experienced reloaders out there. I have been developing different loads with accuracy for a goal. I have been working on this off and on for about 4 years. At this point, I have developed 4 sub-M.O.A. loads with 4 different powders but all with Hornady 168 gr BTHP Match bullets. But for all of these loads i have been FL sizing each case.

Would there be any advantage to fire-forming the brass and then neck sizing only? Could this potentially cause cartridge chambering issues? Would the brass need to be annealed?

Any comments will be greatly appreciated and added to my own personal knowledge base:D

BTW: My rifle is a DPMS 308 Oracle, chrome lined 16" barrel, Sightmark 3X9 scope.



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Thanks for the response. I actually did a search for this topic but didn't find anything. Those are great articles and fully answered my question. Full length it is
 
Those are great articles and fully answered my question. Full length it is
Click to expand...

Not really, to cut down on case travel I sized the case to off set the length of the chamber. The full length sizing die is designed to return the case to minimum length/dimensions. For the 30/06 the difference in length between maximum length from the shoulder to the case head to minimum length is .005".

After that it gets complicated because reloaders believe they can neck size a case 5 times after firing and then start over by full length sizing and I always ask; how do they do that? The case has been fired 5 times. the only way I can figure that one out is to consider some reloaders have an exemption to case hardening. My cases take on a resistance to sizing, the more I fire them the more difficult it is to return them to minimum length.

F. Guffey
 
I'll add that I've measured a lot of new cartridges over time, and found commercial new (not reloads) 308 W ammunition is pretty consistently made 0.002" shorter from head to shoulder datum than the minimum chamber standard (1.630"). There is seldom a feed issue with factory ammunition. So, if you run your cases into your FL sizing die just far enough to make them 0.002" shorter than your chamber is, you will be fine.

At moderate loads, cases eject about 0.001" shorter than the chamber due to spring-back, so resizing those cases just 0.001" shorter than as-fired is theoretically adequate and works the brass least. However, some near-max loads don't have that spring-back and those hot enough to create sticky bolt lift will have compressed cases that actually spring out longer than the chamber at ejection. Some self-loaders, like your AR bend rims, so the case can measure longer than the chamber is. So, if you want to work the brass least, see if you can find someone with a set of armorer's headspace gauges to determine what your gun's headspace actually is. Measure the longest gauge that GO's into the chamber using your own measuring tool to see what it reads, then resize at least 0.002" shorter than that number, whatever it is.

If you have a deft hand with measuring, in lieu of the headspace gauges, you can strip the ejector from your bolt and use a new case with various shims under its head on the bolt face to learn how many thousandths over that new case's head-to-shoulder measurement your chamber headspace is, and so skip out on the formal use of the headspace gauges. But I know people I would not trust to make such a measurement accurately without a lot of practice. Many can't use the headspace gauges correctly, much less feel brass against the shoulder accurately. This is call you'd have to make.
 
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