Headspace, Accuracy and Reliability
Proper headspace is paramount to consistency.
Consistency is paramount to accuracy and reliability.
Headspace is considered primarily to effect accuracy. This is because the subject of most if not all writings has been the boltgun.
Most of us have read about or experimented with headspace enough to form the opinion that keeping it to a minimum is conducive to an accurate rifle or pistol. This conclusion is true. Headspace determines the seating depth of the cartridge which in turn determines the relationship of the cartridge rim to the bolt face and firing pin.
.042"-.043" is optimal in my opinion and will insure consistent seating of the cartridge. Less is not more in this application however. If a particular lot of ammunition has an average rim thickness of .040" you will not see any positive results from headspacing your bolt to .039" or .040" (zero headspace).
Using the rim to establish headspace increases inconsistent seating of the cartridge. As we know the bolt of an autoloader needs sufficient clearance within the receiver for cycling and since the bolt cannot be placed in exactly the same position with exactly the same pressure on the cartridge rim from shot to shot a little wiggle room has proven to be far more consistent and therefore beneficial to accuracy.
Would .041"-.044" be okay? Yes. Just make sure your headspace is greater than your rim thickness and dont go over .044". Also there is no such thing as a slamfire.
Increasing headspace beyond .044" has a dramatic effect on consistent ignition.
As headspace increases the space between the breech face and the boltface increase. This allows the cartridge to seat to different depths from shot to shot and limits the firing pins travel accordingly. If your headspace is .050" and your rim thickness is .040" then you have a cartridge rim that will be anywhere from .001"-.010" away from the breechface each time the firing pin strikes it. Not only does this causes the firing pin to push the cartridge forward to seat it prior to striking the rim for ignition but it also eliminates .010" of firing pin protrusion. This pushing of the cartridge absorbs the firing pins energy, limits the firing pins impact and causes inconsistent ignition.
If your excess headspace is .002" then you will experience a 2.5% variation in seating consistency. If your excess is .010" then you will experience a 10% variation.
Calfee states that headspace is not important however I dont think he realized that his .013" oversize firing pin not only reestablished ignition but was actually seating his cartridge and therefore reestablishing headspace.
Adjusting your headspace can have a negative effect on reliability.
As we know the headspace of factory bolts varies greatly. I have measured bolts which ranged from .037"-.054" and all used the same extractor. An extractor that allows .054" of rim is fine for a rim that is .051" but is far too long for a .040" rim. This factory extractor allows the cartridge rim to shift fore and aft .014" which in turn creates inconsistent positioning of the cartridge rim. If the rim is not in the same place with the same extractor tension from shot to shot it will not contact the ejector properly. You can hit it with a hammer, file a groove in it or color it black but it is still a 3 cent stamped factory part.
Generally you need .003"-.005" clearance between the cartridge rim and the nose of the extractor. This will keep the extracted case rim close to the boltface preventing it from tipping and will insure it stays square to the ejector.
Keep these things in mind when building your next rifle and I believe you will see positive results.
TKidd Headspace, Accuracy and Reliability - RimfireCentral.com Forums
This guy knows his stuff