How to accurately measure (not validate) headspace?

[arch408]

Measure scotch tape. Put layers on "go" one at a time until the bolt has resistance. Add the tape layer thickness to the gauge length.

 

[Mram10us]

That's a pretty clever suggestion, thanks. And for Mram10us, the picture was of .223 rounds, but right now I'm working on 6.5CM through a Savage 110 Ashbury, 24" barrel.

Help if I looked at the pics.... thanks

 

[30BR]

Does no one do chamber casts anymore?

 

[Edd]

When I want to know how much longer my chamber is than my go gauge, I put a short strip of oiled .035" diameter rosin core solder on top of the go gauge and close the bolt on it.

 

[freddiej]

Jeff,
Full Length size one piece of brass such that the bolt closes without friction, put a primer in the primer pocket, seat it below the case head, go outside, scare the hell out of the old lady down the street by putting the case and primer in your gun, fire it into the air. then measure the protrusion. this should give you a precise measurement over the 1.556" you say your brass goes down to.

 

[Jeffpatton00]

Jeff,
Full Length size one piece of brass such that the bolt closes without friction, put a primer in the primer pocket, seat it below the case head, go outside, scare the hell out of the old lady down the street by putting the case and primer in your gun, fire it into the air. then measure the protrusion. this should give you a precise measurement over the 1.556" you say your brass goes down to.

I want to make sure I'm following you, Freddie. You're saying that the primer alone would cause the brass to fire-form to the chamber?

 

[RD57]

Old timer way to do it, but it still works. Take a fired/unsized piece of brass and measure it from top of neck to bottom of case centered on primer. If the primer is still in the case make sure it is below flush for the measurement. Once the initial measurement is completed, partially unseat the primer with a universal de-priming die by about .004" so you can slip it out of the shell holder. Re-chamber that piece of brass and extract it. The bolt will seat the primer as far as it can with the shoulder of the case against the shoulder of the chamber. Measure the case again at the same points as before and subtract the first measurement from the last. The value you received is the excess headspace with that case. Measure the same case with the RCBS Prec Mic and add the value you got and will have the exact headspace reference from the Precision Mic. Most cases springback at the shoulder after firing by about .002", my freshly annealed cases spring back .001 - .0015". You can actually do this even with new brass. Measure as before with un-primed brass and then partially priming with a used/fired primer. Using a fired piece of brass gives you a better understanding of how much spring back your case's shoulder moved. Most of my resizing FL dies are set up to leave/maintain the shoulder at the expanded fired length as they are easy to chamber.

 

[rammac]

...is there a good way to accurately and directly measure headspace?

If you really want to know the exact headspace dimension of your rifle then you can buy Incremental Headspace Gauge Kits. They are expensive but they are actually precision gauges that are .001" apart in headspace values.

 

[BountyHunter]

Watch this

Alex has several more key videos

Videos | wheeleraccuracy

www.wheeleraccuracy.com

 

[25WSM]

First off you can't get a headspace length by casting a chamber. It only shows you the actual chamber and not the rest of the space back to the bolt face. 2nd if you shoot off just a primer your case is going to be around . 003 to . 007 shorter after the firing pin strike. With no pressure in the case to expand it back you now have a short case. Remember firing pin springs are around 26 pounds on average and yes they will set your brass back. I've built rifles for 30 yrs and shot compatition for half that and never have I felt that I needed to know my exact chamber length. For reloading purposes you just need a fired case and a comparitor. Even if you get a sloppy job and your chamber is . 002 to . 003 too long it doesn't matter that much as long as you set your sizing die up correctly. If you really need to know what the size of your chamber is just neck size for about 3 to 4 shots and when your brass starts to close with a slight resistance you have it. That's the problem with neck sizing after a few shots your brass fit to tight.
Shep

 

[338 dude]

Does no one do chamber casts anymore?

No And that will not give you the correct distance to the boat face anyway

 

[338 dude]

When I want to know how much longer my chamber is than my go gauge, I put a short strip of oiled .035" diameter rosin core solder on top of the go gauge and close the bolt on it.

There is a post from Dusty Stevens giving example just like that where you could check the distance from your barrel to your bolt face I guess maybe you could also do that on the bottom of a case close the bolt and know your headspace possibly

 

[257RobertsMan]

As others have stated, use a fired case and deprime without re-sizing, measure from datum, partially insert a spent primer and close the bolt and remeasure using the primer as the base. Or take one piece of your brass and neck size only, after 2-3 more firings of the neck sized brass the bolt lift will show some resistance due the the brass being fully sized to your chamber. While doing this check your over-all case length and trim if needed.

 

[Mram10us]

it seems using a go gauge and shims is the only way to get an accurate measurement of headspace. Brass is too soft. Primers are too soft. All will move or form to any pressure from the bolt. We are still confusing the term "headspace".