Finding Lands - Bolt Disassembly

[mbruce]

When not using a depth gauge, why is it recommended to remove the extractor and firing pin when finding your lands, yet both are installed when shooting. I've heard/read you don't want anything pushing on the case, but the case will/may be pushed once you reinstall the extractor and firing pin. Just seems you want to keep everything as would be when shooting, I dunno?

I guess this is a loaded question, but does anyone leave the extractor and/or firing pin in when successfully finding the lands?

Thank you

 

[Coltdriver]

I use an old stony point (now Hornady) tool that lets me press the case gently into the chamber. There is a piece that lets you press the bullet while holding the case in place. Then I take a cleaning rod and work the bullet back and forth a bit so I am not stuffing the bullet into the lands but am just touching the lands. Then I work backwards from there.

I think, to a large degree, that its all slightly variable given the case and the chamber and what really happens when the bullet is fired. But at least I can establish a col to work from.

 

[mbruce]

I use an old stony point (now Hornady) tool that lets me press the case gently into the chamber. There is a piece that lets you press the bullet while holding the case in place. Then I take a cleaning rod and work the bullet back and forth a bit so I am not stuffing the bullet into the lands but am just touching the lands. Then I work backwards from there.

I think, to a large degree, that its all slightly variable given the case and the chamber and what really happens when the bullet is fired. But at least I can establish a col to work from.

Yea, that sounds like what I do now. I use the Sinclair depth gauge for a starting point and then work backwards. I meant when using just the bolt, a case, and a bullet and gently chamber the cartridge.

 

[Bart B.]

The Stoney Point method is best because the case shoulder against the chamber shoulder is the reference point bullet land contact point must be judged.

Case heads are a few to several thousandths off the bolt face when the round fires. It's not a good place to measure bullet to land contact point from. It depends on how much head clearance the case has when chambered and how much the case shoulder's set back from firing pin impact. The spread across case headspace on rimless bottleneck ones determines the spread its head wil be off the bolt face. The difference between case and chamber headspace determines the starting point (head clearance) to begin with.

 

[Varminterror]

Th Hornady/Stoney point method only really measures the distance from the shoulder to the lands, the case base is floating in space with no real reference to the bolt face. If your Hornady modified case is longer or shorter than your actual headspace, the coal's determined by using it are meaningless. These cases must be accompanied by an non-resized fired case to establish the offset reference for coal. It IS the best method, but it's not proper without a reference case.

The question asked - why remove your extractor and ejector - is to ensure the case base is dead length seating between the chamber shoulder and the bolt face. Not seating against the spring loaded ejector, or held off kilter by the extractor, giving a falsely short headspace reading.

 

[Bart B.]

In all my tests, the firing pin drives the rimless bottleneck case shoulder hard into the chamber shoulder before the round fres. Regardless of the extractor or ejector type and the case head at some place at the back end based on where it ends up from firing pin slamming into the primer. The case head may or may not be against the chamber wall from extractor force.

 

[mbruce]

The question asked - why remove your extractor and ejector - is to ensure the case base is dead length seating between the chamber shoulder and the bolt face. Not seating against the spring loaded ejector, or held off kilter by the extractor, giving a falsely short headspace reading.

Ah, I figured. It seems like the distance to the lands without the ejector and extractor changes once the ejector and extractor are installed. But if you stay in the hundredths jumps then I guess you allow yourself some wiggle room.

Here is the video I watched that led me to the OP:

 

[Offfhand]

Sometimes ya' just gotta shake your head and wonder why something so simple is made so complicated. Measuring cartridge length with bullet contacting lands is quickly and easily done with only a cleaning rod, wood dowel, caliper and bullet. No need for the case or reason to remove firing pin or extractor.

 

[Bart B.]

I've not seen any significant difference in accuracy through 600 yards as bullet jump increased .050 inch in the same chamber over 2000 rounds of the same lot of ammo from normal barrel erosion.

All my rifles have their extractors pushing case heads off center some amount whether an ejector or extractor is installed or not. Case shoulders are hard into the chamber shoulder when fired regardless of extractor or ejector position.