why do I need to resize cases from my AR-15

but I also know my AR can close the bolt on a +0.002" case. Somewhere around +0.005", it will not.
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How are you closing the bolt when it closes on a +002 case ? I ask because I've done a good amount of testing on this issue and I can confirm that if you let the BCG fly home from the locked back position . The force of the case shoulder slamming up against the chambers shoulder will set the shoulder back about .0015 to .0025 each time that round is chambered . I did these test with a fully assembled bolt , stripped bolt and every combo in between . I have also found that same length case when chambered by holding the bolt back and slowly riding it home then using the forward assist to force the chambering will not close . That's light to medium/light tapping on the FA .

When I tested the effects of the BCG slamming home I used cases that were sized .002 shorter then my fire formed cases . I repeatedly chambered the same round until set back stopped . They were set back an avg of .001 to .0015 each time chambered . The set back stopped around a total combined set back of .005 . I then sized cases to .005 and .007 shorter then my fire formed cases and did the test again . The .005 cases had a couple set back about .0005 ( but that difference could easily be the ability of my calipers to measure that small of an increment ) and the .007 did not have any set back .

I used three different AR's and ran the same test with each . The results were virtually identical with some minor differences but the end results being the same . The BCG flying home will set back the shoulders of a loaded round and at some point the cases get to short for set back to happen . somewhere around .005 to .007 short of chamber length .

I posted all that to explain that a +.001 or + .002 case can chamber when the BCG slams home . However IMHO that is not how one should size there cases or when sizing except a few long cases as GTG .

I'm not sure why but I'm a stickler for my cases being sized perfect . I use competition shell holders and almost all my bottle necked cases are sized to with in .001 of each other regardless of caliber. If I'm off on my target length when sizing for semi autos . I only except cases that are shorter then my target length and never longer even though I know my AR's will likely chamber the round .
 
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great discussion and very helpful at getting me there!! Thanks to all!!

I'm about to plop down for a Rockchucker and RCBS competition dies. I plan to work my way through the resizing and measuring/trimming cases with a Lyman case prep gizmo and case trimmer.

At present I hand de-prime and wet tumble my brass.

All my brass is once fired in my Wylde 223 and I will look at headspace with a Hornady head space gauge after resizing.

As best I can tell from all the experienced voices here, I need to:
1. resize my brass
2. measure headspace
3. hopefully this will be consistent after resizing. After resizing do I need to adjust and set the headspace back 0.002 or so??
4. then resize again ??
4. then trim to ???. Not sure what the trim length should be based on the responses.

Sorry to be so dense and thanks for the patience.
Any thoughts on my choices?

thanks again,
t
 
- When starting out with a a gas gun, I recommend full-length resize each and every time
Toss after [X] reloads. 223 brass is too cheap to not buy that insurance.

- When brass reaches 1.760 [after resizing], trim back to 1.750






* "X" varies -- start checking w/ a paperclip after a half dozen.
Rate of measured case stretch/need to trim (after resizing) will
give you an idea.
 
Don't go (much) below 1750" when trimming cases. Operating range is actually
anywhere between 1.750 & 1.760

Cartridge overall length is not dependent on the case length. It's what
you seat the bullet to in overall dimension regardless of case.
 
Not sure what you mean by "operating Range", but the 223 has a SAAMI Range of 1.730-1.760.
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Because 1.750" is the recommended trim-to length by most all reloading
manuals to maintain consistent neck lengths as 'best practice'.

(I would also observe that allowing/ignoring a 30-thousandths case growth
in a repeated-fire reloading sequence is not .... "healthy" ;) :D )
 
great discussion and very helpful at getting me there!! Thanks to all!!

I'm about to plop down for a Rockchucker and RCBS competition dies. I plan to work my way through the resizing and measuring/trimming cases with a Lyman case prep gizmo and case trimmer.
Click to expand...

You might look at their X die, I don't use them but know folks that do and like them.

http://www.midwayusa.com/product/519159/rcbs-x-die-full-length-sizer-die-223-remington

Reports have been that you only have to trim cases one time if you use them.
 
To keep it is very simple terms you need to resize your brass using either a Full Length or Small Base die set because of reliability issues with semi-autos.

I use the following load in my current AR

69 Grain BTHP Hornady bullets
24 Grains of Varget powder
CCI #400 primers
mixed brass

I use Full Length resizing dies, I trim my cases and because my press is an old Lyman rotating single stage (which is WAY more awesome then a standard single stage) I take the time to measure every load to make sure it's consistent

I also don't use cantilevered bullets or crimp them.
 
what do you use to measure your powder?
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For 40 years it was a standard balance beam:
sxn9yg.jpg


Now it's the RCBS ChargeMaster (backed up by the balance beam.

Whatever you do, don't rely on the Lee "Safety" Scale.

.
 
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