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Old April 16th, 2018, 09:24 AM #11
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Thank you all for the response now I know a little more about auto loaders.
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Old April 17th, 2018, 05:56 AM #12
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For a single rifle. Set your die to bump the shoulder back 3 - 5 thousandths. That is enough to easily chamber.

If you have more than one, you can set to size 3 - 5 thousandths shorter than the small chamber rifle.

Actually, semi auto brass have so many stresses, that the difference in case life is not huge.
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Old April 17th, 2018, 06:07 AM #13
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Quote:
Originally Posted by Major03 View Post
Could it not be both reasons?

OP...what's the concern about just full length sizing? Extending case life or trying to maximize accuracy?

I've found quality dies produce ammo just as concentric and accurate as neck sizing only dies. Forster and Redding Competition dies are fantastic.

If you're looking to work the brass less, you could always use a body die to bump the shoulder back and then neck size. Or anneal your brass to reduce the work hardening.
I also think it is both reasons.

Me, I'd be paying to lot more attention to having .223 brass that works, than I would to working .223 brass. But that's I suppose another discussion.
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Old April 17th, 2018, 06:31 AM #14
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Neck sizing is mostly used as a additional accuracy tool in bolt guns or to keep cases from splitting in guns that have oversized chambers. I see no advantage at all for neck sizing in an AR. My biggest issue with the 300BO in an AR is primer pockets opening after only a few reloads but that is because I am shooting 150 gn at supersonic speeds and using any make of brass.
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Old April 17th, 2018, 01:54 PM #15
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Quote:
Originally Posted by PowPow View Post
Found this interesting and relevant:

Shoulder Bump − How Much Do You Really Need?
If the die bumps the shoulder then hasn't the case been fully sized? I don't know how much the shoulder moves upon firing but postulate that any movement would be at rear of case if headspace was wrong.
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Old April 18th, 2018, 02:18 AM #16
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It is, but we cannot push the brass back into the bottom of the case.

And this why, oversize chambers are an issue. Every time you fire, the case gets longer, mainly near the case head. Then we resized the case, moving the shoulder back.

Two things happen. Over time, the neck become thicker. And more problematic is that the brass near the case head ends up getting thin and caused a case head separation.

If you shoulder bump, yes, you are sizing the whole case. But not to minimum size. The cases have some taper, so if we do not run the case fully into the die, we are not reducing the diameter completely.

Neck sizing only assumes that your chamber is perfect and the bore is completely centered. If the chamber has a curve, or some oval shape, neck sizing only can increase issues.
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Old April 18th, 2018, 07:17 AM #17
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One could also get a case gauge that indicates SAAMI max and min for ammo and bump everything back to inside that range. Often getting to SAAMI max is a 0.001" to 0.003" bump (obviously varies gun to gun). Something like a Dillon case gauge.

One advantage to neck sizing only is that when using a Lee collet neck die (great die btw), is that you do not need to use any lube. It's a great way to churn out very accurate ammo quickly with minimal fuss. Generally not appropriate for an AR15 though.
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Old April 19th, 2018, 05:53 AM #18
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+1 Pinecone and you may not get full bolt lockup in an AR with necksized cases.
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Old April 19th, 2018, 09:38 PM #19
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I understand a few things about semi auto rifles regarding cartridge fit and chamber dimensions that a chamber with a slightly generous fit to cartridges a good thing.
The first one is primer firing pin clearance. When head-space is on the tight side like a minimum head-space chamber and a + head-space cartridge are combined make sure primers are below flush. Sometimes cases that have been crimped have a concave head. This can happen during the manufacturing process when the primers are crimped. It also can be seen with varying primer heights when reloading. Bolt speeds alone are enough to detonate an overly sensitive primer before lugs are fully engaged and things like this can make trouble by contributing to a slam fire, OOB or even if hammer follow through happens.
Another thing is the additional radial clearance can help minimize heat transfer. In rapid fire weapons minimizing cook off whether it be from a primer right up against the bolt face tightly or heat transfer to the cartridge through the chamber walls.
Chamber necks that have become to thick too long or bullets that are seated to the throat can exacerbate problems with dirty, mis-reamed chambers and parts wear aggregate. Or a long firing pin for that matter.
The act of a rapidly closing bolt usually makes the the remaining case size needed to make it fit well in an auto loading rifle and that's what can cause problems if the case is a close fit with the chamber. Full length resizing can promote better performance by making sure head-space is not to long by a shell holder that's thin or a press that's not completely cammed over center.
Auto loading rifles are more susceptible to problems associated with cartridge fit just due to the nature of the design their purpose and lack the power to extract or seat a poorly fit cartridge just like pumps and lever actions so full length resizing could be considered a best practice in my view.

Some auto loading rifles I own I intentionally finished reamed over Saami gauge length and allows for below a no-go gauge tolerance. Just because I cant accurately account for dimensional clearances with worn parts. Receivers bolts etc.
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