head space, throat, bolt gun

[nfngun]

Ok I'm picking up an RCBS MIC to measure head space, the question once i take a measurement at what point do i bump the space back, I will take the measurement off the once fired brass once the brass starts to feel tight should it be bumped to my once fired specs or should i move it back .002 from that measurement?

Same for the neck length once i get the tool and get a measurement how much should i cut it back from that measurement?

 

[MitchAlsup]

Re: head space, throat, bolt gun

What I did: I started by Neck Only sizing a few round, and finally ended up with 3 cases. The first case has no noticible force required to close the bolt on my gun, the second has just a smattering of force required, the third has considerable force required. All three cases measure within 0.001 of each other in my RCBS case micrometer. I segregated thes cases and marked them for future use/measurements. I then used new cases and the RCBS case micrometer to setup the sizing die (body die in this cae)position shoulders of new brass to the sholder position of the first case (above) or slightly shorter than the first case above.

Notice that I did not use the absolute scale on the RCBS case micrometer, just the relative dial to find the length of my chamber's shoulder position.

 

[Ratbert]

Re: head space, throat, bolt gun

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: MitchAlsup</div><div class="ubbcode-body">What I did: I started by Neck Only sizing a few round, and finally ended up with 3 cases. The first case has no noticible force required to close the bolt on my gun, the second has just a smattering of force required, the third has considerable force required. All three cases measure within 0.001 of each other in my RCBS case micrometer. I segregated thes cases and marked them for future use/measurements. I then used new cases and the RCBS case micrometer to setup the sizing die (body die in this cae)position shoulders of new brass to the sholder position of the first case (above) or slightly shorter than the first case above.

Notice that I did not use the absolute scale on the RCBS case micrometer, just the relative dial to find the length of my chamber's shoulder position.</div></div>

Good method.

 

[Hookturnr]

Re: head space, throat, bolt gun

I have set mine up in a similar way. I use the hornady headspace gauge and measure around 12 once fired cases to develop and average of what I think the fired headspace # is. My measurements tend to be +/-.001 in this process. I then set up my die to resize to an avrage of .002 shorter than the number I obtained on the fired cases. I resize several at this setting and then check that they consistently chamber with no extra force in my gun and go from there. I've found that .002 is NOT an absolute number. It's usually where you want to be but i've got one tight chambered gun that needs .004. Just my experience...

 

[nfngun]

Re: head space, throat, bolt gun

Will a neck sizer help stretch the neck enought to be able to cut back in .001 increments or will i need to keep shooting the case to do it? I dont mind turning 30 cents of brass into templates vs buying a tool to measure ...

 

[targaflorio]

Re: head space, throat, bolt gun

Neck length? Do you mean the trim to length? You can measure your chamber to determine that, but Saami spec is easy enough.

The Rcbs precision mic is great for measuring the fired case head space and then adjusting your sizing die to bump the shoulders back your desired amount. .002" is a good number for a bolt gun.

If you shoot the same brass out of your bolt gun, then you can neck size only and get the ammo to chamber for the first several reloads, at least.

 

[Martin55]

Re: head space, throat, bolt gun

I then set up my die to resize to an avrage of .002 shorter than the number I obtained on the fired cases.

 

[nfngun]

Re: head space, throat, bolt gun

Thanks you all for the info my rcbs mic should be in today now i can get into headspaceing and ogive.