Just thought I would share a method I havn't seen elsewhere for headspacing. I have been accurizing my 45x's for a while like this and also checking/fitting replacement barrels on the 455's this way for proper headspace.
Normally I use headspace gauges in .001 increments and work my way down until I find the maximum size. A bit time consuming and this rifle's bolt needs to have the striker spring installed on the test to have the bolt properly cam shut. That spring resistance on the closing adds a bit of uncertainty in the measurement compared to bolts that are stripped for testing by feel alone.
In this procedure I use Plastigage which for those who are not familiar with; its a small plastic string like material that deforms between mating surfaces and can be measured acurately to a scale that comes with it. The stuff I get comes in two range sizes, .0001"- .003" and .002- .006". Its used primarily to measure bearing clearances on engine assemblies. Costs about $8 an there is enough to do a few dozen readings.
This is how the plastigage comes in red or green for the two ranges..
I put a touch of spit on either side of the bolt face so that the small strip of plastigage will be held in place as I insert the bolt in the rifle...
I tried this one on a unfired casing (bullet pulled) that had a measured rim thickness of .041". When the bolt is retracted the guage sticks to the back of the shell and then measured against the scale...this one shows a touch over .006" clearance...or a headspace of aprox .047" on this CZ 455. I only did this because some folks out there might not want spring for some headspace gauges so this test will work with casings also.
Since shells are not perfect in regards to rim thickness, flatness/squareness on their back and the fact that bullet engraving/resistance may give a false reading. ** NOTE ]It is not safe to use a live round for this test on a newly installed barrel without confirming you are on the plus side of clearance using a fired casing first. I recomfirmed the measurement using a .045 brass headspace gauge. The smaller green range plastigage is used here, and confirms the previously measured .047" headspace perfectly..
I find this method gives a really exact measurement that does not rely on feel since it measures from full bolt closure. It also does not require stripping the striker or the bolt down except the extractor/ejector claws. Some bolts such as the 452's/455's also tilts upwards a touch from the sear pressure under the striker before firing...this method measures the headspacing with this taken into account unlike a stripped bolt that sits in a relaxed state on closure.
The gauge has the benefit of showing a misalignment if the deformed strip appears wedge shaped, normal headspace guage only measures the highest spot of contact and gives no indication of non parallelness between the bolt face and the breach.
You can also put the plastigage on the front bolt face and measure clearance to the breach face quickly in the same way. System works well for bolts that don't rotate shut on their faces such as the CZ's. Rotating surfaces would cause the gauge to smear, not compress.
Anyways, for those who buy a switch out barrel on a 455 and don't have access to a competant gunsmith to check the clearances, this is an easy way to do so.
Normally I use headspace gauges in .001 increments and work my way down until I find the maximum size. A bit time consuming and this rifle's bolt needs to have the striker spring installed on the test to have the bolt properly cam shut. That spring resistance on the closing adds a bit of uncertainty in the measurement compared to bolts that are stripped for testing by feel alone.
In this procedure I use Plastigage which for those who are not familiar with; its a small plastic string like material that deforms between mating surfaces and can be measured acurately to a scale that comes with it. The stuff I get comes in two range sizes, .0001"- .003" and .002- .006". Its used primarily to measure bearing clearances on engine assemblies. Costs about $8 an there is enough to do a few dozen readings.
This is how the plastigage comes in red or green for the two ranges..
I put a touch of spit on either side of the bolt face so that the small strip of plastigage will be held in place as I insert the bolt in the rifle...
I tried this one on a unfired casing (bullet pulled) that had a measured rim thickness of .041". When the bolt is retracted the guage sticks to the back of the shell and then measured against the scale...this one shows a touch over .006" clearance...or a headspace of aprox .047" on this CZ 455. I only did this because some folks out there might not want spring for some headspace gauges so this test will work with casings also.
Since shells are not perfect in regards to rim thickness, flatness/squareness on their back and the fact that bullet engraving/resistance may give a false reading. ** NOTE ]It is not safe to use a live round for this test on a newly installed barrel without confirming you are on the plus side of clearance using a fired casing first. I recomfirmed the measurement using a .045 brass headspace gauge. The smaller green range plastigage is used here, and confirms the previously measured .047" headspace perfectly..
I find this method gives a really exact measurement that does not rely on feel since it measures from full bolt closure. It also does not require stripping the striker or the bolt down except the extractor/ejector claws. Some bolts such as the 452's/455's also tilts upwards a touch from the sear pressure under the striker before firing...this method measures the headspacing with this taken into account unlike a stripped bolt that sits in a relaxed state on closure.
The gauge has the benefit of showing a misalignment if the deformed strip appears wedge shaped, normal headspace guage only measures the highest spot of contact and gives no indication of non parallelness between the bolt face and the breach.
You can also put the plastigage on the front bolt face and measure clearance to the breach face quickly in the same way. System works well for bolts that don't rotate shut on their faces such as the CZ's. Rotating surfaces would cause the gauge to smear, not compress.
Anyways, for those who buy a switch out barrel on a 455 and don't have access to a competant gunsmith to check the clearances, this is an easy way to do so.
