Headspace question

[Thaught]

Have a new rifle I just built chambered in 30 Nosler. I started with new ADG brass and shot 50 rounds through it to break in and kind of get a start in load development. Most of the brass is coming back at 2.1835” after being shot, and 2 are coming back at 2.1850”. Looking at my reamer print out, it’s showing a min of 2.1877” and max of 2.1977. So my question is this… would it seem that I should only neck size these since they did not get blown out all the way to the exact chamber dimensions? I did take the 2 biggest pieces and

 

[NZ_Fclass]

Best to check the SAAMI chamber drawings - they are all online, but it can be a fiddle to find them

 

[Benchrest Braxton]

does the brass rechamber easily? if so, neck sizing would be fine. full length sizing is also fine and will actually help you achieve fireforming your headspace quicker (full length resizing without touching the shoulder actually pushes the shoulder forward).

 

[jackieschmidt]

When you did the initial firing to fireform your brass and break in the barrel, did you put a very thin film of case lube on the case bodies to insure that the case did indeed come back against the bolt face and fully form?

 

[MikeRu]

I’m not sure your headspace tool (BTW what are you using?) is measuring anything that could be in the reamer print. My Hornady stuff only gives relative numbers. See if 1-2 pieces of scotch tape applied to the base of the case will prevent chambering. Use your calipers on these taped cases to see what max “base to shoulder “ is, then bump all your cases so they have about 2 thou (0.002”) of clearance. You might want to remove your firing pin and ejector pin and use bolt drop to determine max headspace in your chamber.

 

[L.Sherm]

MikeRu nailed it, not all comparators measure right on the datum line.
Do the Alex Wheeler stripped bolt method, it is in my opinion only way to get resistance free bolt close measurement.

 

[Thaught]

I’m not sure your headspace tool (BTW what are you using?) is measuring anything that could be in the reamer print. My Hornady stuff only gives relative numbers. See if 1-2 pieces of scotch tape applied to the base of the case will prevent chambering. Use your calipers on these taped cases to see what max “base to shoulder “ is, then bump all your cases so they have about 2 thou (0.002”) of clearance. You might want to remove your firing pin and ejector pin and use bolt drop to determine max headspace in your chamber.

I’m using the hornady headspace tool

 

[K22]

The process I use for virgin cases (new) is to measure the case head space with a bump gauge. I select a sample, for example 10 out of a bag of 50. I set my F/L die to size the largest to zero bump. I spot check in the rifle to make sure it will chamber without issue. I mark the head of the case with a sharpie.

After firing, I check and record the fired case head space to assess the amount of expansion. Usually, they have expanded but not always. I spot check the largest case head space in the rifle to assess chambering. Then I full size with zero bump or more if necessary. Almost always, no bump is needed.

I don't see why a neck sizing die might work for the initially fire forming. However, the reason I like using the F/L die is that I have discovered that I can go several firings without bumping the shoulder. I suspect this is due to the fact that the F/L die also sizes the radial dimension of the case which may be the major contributor to difficult sizing. With a neck die, you will never know if it's the radial or head space that is causing the difficult chambering, if and when it occurs.


PS: I use Skip shims to make adjustments to my F/L die. This is an easy method to make adjustments without having to mess with the F/L die lock ring. I just substitute an appropriate size shim to change the sizing. Works like a charm, at least for me.

 

[243winxb]

should only neck size

Yes. When bolt has a crush fit, when chambering, measure head to datum, then.

 

[gunsandgunsmithing]

Fwiw, you can't use a comparator to get accurate actual headspace measurements. They simply are for comparing two cases, not for providing a reliably ACCURATE measurement. They can accurately tell you how much difference you have between two cases, though.

Simply put, they are what they are...a comparator but not a tool to give a reliable measurement to match your print or actual chamber dimensions.

 

[Thaught]

thanks everyone. I watched the Eric Cortina video and used his method using scotch tape to find actual headspace dimension. The proper headspace on my rifle is 2.1850”. I will FL size the brass but will be careful not to bump the shoulder on this next firing.

 

[Coyotefurharvester]

I have found a partially seated(0.010 proud) spent primer gives an accurate, quick, measurable bolt to cartridge base measurement. But you need to check/measure several(10 or more) cases to get the best results for setting up full length sizing die. I'm sure this follows for all the different methods of measuring headspace and adjusting die. One or 2 cases aren't enough, as your not seeing the whole range of variance after one firing.

 

[B Nettesheim]

Tim
Are you measuring your headspace gauge with the same comparator as you are using for the cases?