Full Length or Neck Only; What's Best Resizing for Accuracy?

[Mram10us]

I think a 2 to 3 ounce firing pin pushed near 20 fps by a 25 pound spring force would very tightly press the case shoulder into the chamber shoulder. Sometimes setting the case shoulder back a couple thousandths.

Is the back of the chambered case body ever pushed against the chamber by the extractor claw?

I don't think the firing pin helps, because the expanding case fills the chamber and presses back into the boltface. I guess an experiment could help.
Take 5 cases and set the shoulder back in .004" increments. Would they all fireform or would they separate?

 

[okie man]

What if you're using a controlled round feed action? No ejector button pushing on one side of case head? I size my cases for my cz actions very close to the shoulder and have shot some great groups with them. My next step in the learning curve for extreme accuracy is turning necks and annealing

 

[Orange Dust]

What if you're using a controlled round feed action? No ejector button pushing on one side of case head? I size my cases for my cz actions very close to the shoulder and have shot some great groups with them. My next step in the learning curve for extreme accuracy is turning necks and annealing

I don't think it matters much. I have both types and they shoot equally well. I size my cases so you can feel them seat closing the bolt.

 

[Bart B]

What if you're using a controlled round feed action? No ejector button pushing on one side of case head?

doesn't the controlled round feed extractor push against the case groove pushing the case head sideways against the bolt face shroud as the case comes out of the chamber before the ejector pushes it off the bolt head?

 

[Orange Dust]

doesn't the controlled round feed extractor push against the case groove pushing the case head sideways against the bolt face shroud as the case comes out of the chamber before the ejector pushes it off the bolt head?

Yep

 

[bigngreen]

doesn't the controlled round feed extractor push against the case groove pushing the case head sideways against the bolt face shroud as the case comes out of the chamber before the ejector pushes it off the bolt head?

Many CRF actions move the claw out in a bump so its not holding the case when in the firing position, not all but some.

 

[Bart B]

I don't think it matters much. I have both types and they shoot equally well. I size my cases so you can feel them seat closing the bolt.

I think it was Ferris Pindell, a tool and die machinist at Sierra Bullets, who convinced them in the 1950's to full length size their fired cases setting shoulders back a thousandth or 2 so bolts would close without any resistance. This oriented the bolt head very repeatable from shot to shot. Smallest groups were the results. Sierra's full length sized all cases since then

Mr. Pindell was a partner with Dr. Lou Palmisano, the two benchrest winners that developed the PPC cartridge family.

 

[Bart B]

Many CRF actions move the claw out in a bump so its not holding the case when in the firing position, not all but some.

Very interesting. Which ones do?

Please explain the mechanics involved.

 

[bigngreen]

They just have a ramp in the locating groove that lifts the claw slightly right at the end of closing.

 

[Timeout]

IMHO the ideal situation is to send a twice or three times fired case to Whiddens (or any other reputable custom die maker) and have them build you a die that is dimensioned according to your fired cartridge cases. This creates the benefit of less stress on your brass from sizing it down way more than is necessary and equates to many more loading-firing cycles before having to discard the brass. It would also eliminate the aforementioned excessive clearance between the chamber and your resized brass. I think that today you will find most experienced benchrest guys/gals are full length sizing. When done correctly with properly sized dies, it is superior to neck sizing only. As mentioned earlier in this thread, there are a number of factors that contribute to "runout" of the loaded cartridges.

 

[Timeout]

I don't think the firing pin helps, because the expanding case fills the chamber and presses back into the boltface. I guess an experiment could help.
Take 5 cases and set the shoulder back in .004" increments. Would they all fireform or would they separate?

This much I can tell you from experience, if you push the shoulder too far back, you will begin to have misfires. The commonly held practice is to set your FL die up for .002" shoulder bump with regards to the fired case dimension. In a perfect world looking for maximum accuracy, some set up their die to create a very slight resistance when closing the bolt. That of course is done with the firing pin and ejector removed. This forum is Long Range Hunting, so for all practical purposes IMHO the .002" shoulder bump is sufficient. One thing I do on my Rem 700 actions used for hunting is to trim the ejector spring to lessen the amount of force against the side of the cartridge case head. Whether it helps accuracy or not, I don't know. I do know that it drops the spent cartridge a lot nearer to where I'm standing and makes it easier to recover. Not a big deal when hunting, but it sure helps during practice and load development.

 

[Bart B]

Regarding runout, specifically that of bullets, no commercial runout gauge positions cartridges to the dial indicator like they are in the chamber when fired. There are no standards for cartridge reference points.

 

[aushunter1]

Imho the 'neck sizing only' role isn't to obtain accuracy(or at least more than FL sizing), it is to work the rest of the brass less & prolong its life.
Of course you will still need to bump the shoulder back at some point & you will still need to anneal the brass every so often but not nearly as much as if you just FL size.

 

[Bart B]

I and others have got well over 40 reloads per 308 Winchester case with max loads bumping shoulder back a couple thousandths. Had to trim case back about .008" after every 10 reloads.

Cases shortened about .002" when fired then lengthened near. 003" after full length sizing in standard RCBS dies.