Headspace question/scenario

[Thaught]

I am trying to figure out the headspace on my new 30 Nosler. I loaded up 22 rounds with new ADG brass for barrel break in. After I shot those rounds I measure the fired brass with my Sinclair comparator. I’m coming up with several different measurements, which is fine and somewhat expected. Here’s where I’m getting lost…

I pulled the firing pin and ejector from the bolt so there is zero resistance

Brass #1 is measuring 2.1720” and loads in the chamber fine and the bolt closes with zero resistance.

Brass #2 is measuring 2.1625” and is very hard to close. The necks diameters are the same for both as I was thinking maybe the neck on brass #2 was blown out and causing a hard bolt.

Brass #3 is measuring 2.1635” and closes with zero resistance. I add a layer of scotch tape to the case head which increases the length to 2.1650” and the bolt closes with some resistance. I add a second layer of tape and the length increases to 2.1665” and the bolt will not close.

How is it possible that the longest case is closing fine, the shortest case won’t, and is my scotch tape process accurate?

 

[memilanuk]

Ten thou variance in headspace on 1x fired brass seems excessive to me, personally.

Neck diameter and shoulder setback aka 'headspace' aren't the only places that fired cases can vary in dimension and cause different 'feel' when chambering. The case diameter just below the shoulder, and at the case web, are two places that frequently cause cases to feel like they're hanging up even though the head space at the shoulder seems like they should be fine.

The weird part (to me) is that these were all fired in the same gun, presumably once? yet vary so much. Were some fairly hot, or some very low / starter loads, i.e. to where some cases didn't fireform completely?

 

[rwj]

How is it possible that the longest case is closing fine, the shortest case won’t, and is my scotch tape process accurate?

The bolt not closing freely is not the result of contact between the case and chamber shoulders. New cases can require several firing cycles to expand enough axially for contact to occur at this location.

Adjust your sizing die to only contact the tapered case body, size only enough to permit free bolt closing. Reload and fire the cases, then repeat the body only resizing operation adjusting the die downward as necessary to achieve free bolt closing. After several firings, it will not be necessary to adjust the die downward. This indicating that the case has fully expanded both radially and axially to the chamber.

During this process, continue to monitor overall case length to ensure the case neck end face is not contacting the chamber. Trim as required.

 

[Coyotefurharvester]

What were the new case(unfired) comparator numbers? What were the loading components used, coal, charge weights? What die set are you using?

 

[Thaught]

Ten thou variance in headspace on 1x fired brass seems excessive to me, personally.

Neck diameter and shoulder setback aka 'headspace' aren't the only places that fired cases can vary in dimension and cause different 'feel' when chambering. The case diameter just below the shoulder, and at the case web, are two places that frequently cause cases to feel like they're hanging up even though the head space at the shoulder seems like they should be fine.

The weird part (to me) is that these were all fired in the same gun, presumably once? yet vary so much. Were some fairly hot, or some very low / starter loads, i.e. to where some cases didn't fireform completely?

Powder charges were the same.

 

[Bill Norris]

On a first firing of cases the brass moves more in one place than another on each piece of brass. This causes the different measurements from piece to piece across the various lot. Once all of the brass has been fired at least once or maybe twice more then a more even set of numbers should show.

 

[RegionRat]

+1 with Bill, there is more to chamber fits than just the headspace datum length.
There is/are also the diameters to consider, and also the differences in facets (corner radius shapes) between chambers and virgin brass, and dies.

Take all the important measurements, not just the shoulder datum length. For example, pull the specs for the ammo and chamber, and break out the micrometers.

Neck Diameter
Shoulder Diameter
0.200 line diameter Etc..

If the virgin brass is measured at all those locations prior to and after the first cycle, then also when sized, you will find the root cause and as often as not it can be a diametral or corner problem with coordination between the chamber and the dies.

 

[mikecr]

Do nothing but neck sizing for 3 fire formings, then set your die for correct bump per your method.
Quicker forming occurs with deep body dip annealing of new cases.

 

[Thaught]

Ten thou variance in headspace on 1x fired brass seems excessive to me, personally.

Neck diameter and shoulder setback aka 'headspace' aren't the only places that fired cases can vary in dimension and cause different 'feel' when chambering. The case diameter just below the shoulder, and at the case web, are two places that frequently cause cases to feel like they're hanging up even though the head space at the shoulder seems like they should be fine.

The weird part (to me) is that these were all fired in the same gun, presumably once? yet vary so much. Were some fairly hot, or some very low / starter loads, i.e. to where some cases didn't fireform completel

+1 with Bill, there is more to chamber fits than just the headspace datum length.
There is/are also the diameters to consider, and also the differences in facets (corner radius shapes) between chambers and virgin brass, and dies.

Take all the important measurements, not just the shoulder datum length. For example, pull the specs for the ammo and chamber, and break out the micrometers.

Neck Diameter
Shoulder Diameter
0.200 line diameter Etc..

If the virgin brass is measured at all those locations prior to and after the first cycle, then also when sized, you will find the root cause and as often as not it can be a diametral or corner problem with coordination between the chamber and the dies.

I appreciate your thoughts and trying to help me with this. So tonight, out of curiosity I neck sized 6, 1x fired brass. They all have a stiff bolt to close. Firing on and ejector were removed so there is no resistance. Now, where it gets more confusing for me is the neck sized brass has a shorter headspace measurement than the 1x fired brass and the 1x fired brass will close. I took 7 different measurements of both pieces of brass and the neck sized brass is smaller in all measurements. I just don’t get it.

Is it possible the gunsmith who chambered the barrel screwed something up? Maybe the chamber has runout?

 

[RegionRat]

Did you check the diameters?

 

[47WillysGuy]

I appreciate your thoughts and trying to help me with this. So tonight, out of curiosity I neck sized 6, 1x fired brass. They all have a stiff bolt to close. Firing on and ejector were removed so there is no resistance. Now, where it gets more confusing for me is the neck sized brass has a shorter headspace measurement than the 1x fired brass and the 1x fired brass will close. I took 7 different measurements of both pieces of brass and the neck sized brass is smaller in all measurements. I just don’t get it.

Is it possible the gunsmith who chambered the barrel screwed something up? Maybe the chamber has runout?

The stiff bolt closing could gall the bolt lugs. Maybe time to see a gunsmith?

 

[Thaught]

I figured it out. I don’t understand why my solution worked, but it did. So… I had been using my Sinclair 35° comparator to measure the headspace dimensions. Then the thought came to me to use the Hornady comparator (size E insert) and just like that everything fell into place. I’m not smart enough to know how or why that worked, but it did and it’s 100% perfect, verifiable, and repeatable on all pieces of brass.

I would think that the Sinclair with the angle contoured insert would be accurate, but I’ll never use it again. Can any of you explain why the gauge was so far off?

 

[memilanuk]

I remember *one* time, long ago, that the Sinclair steel headspace comparator insert gave me grief, and I switched back to the Stoney Point (pre-Hornady) inserts. It's definitely not the norm.

Best guess? Either something is slightly off with the shoulder angle, or something about how the comparator seats against the shoulder. Whether that's something in the chamber, or something else, no idea. If you have a bore scope it might be worth taking a peek.

 

[rwj]

I figured it out. I don’t understand why my solution worked, but it did. So… I had been using my Sinclair 35° comparator to measure the headspace dimensions. Then the thought came to me to use the Hornady comparator (size E insert) and just like that everything fell into place. I’m not smart enough to know how or why that worked, but it did and it’s 100% perfect, verifiable, and repeatable on all pieces of brass.

I would think that the Sinclair with the angle contoured insert would be accurate, but I’ll never use it again. Can any of you explain why the gauge was so far off?

The best gauge is the barrel chamber as it is what constrains the case each time it’s fired. Second best is a head space gauge machined using the chamber reamer. Last is one of the comparator gauges (Sinclair, Hornady) that only creates line contact on the shoulder. Finding a comparator gauge that works (replicates the chamber) can be a hit/miss process in my experience. Glad you found one that provides the desired outcome…

 

[AlNyhus]

I figured it out. I don’t understand why my solution worked, but it did. So… I had been using my Sinclair 35° comparator to measure the headspace dimensions. Then the thought came to me to use the Hornady comparator (size E insert) and just like that everything fell into place. I’m not smart enough to know how or why that worked, but it did and it’s 100% perfect, verifiable, and repeatable on all pieces of brass.

I would think that the Sinclair with the angle contoured insert would be accurate, but I’ll never use it again. Can any of you explain why the gauge was so far off?

I've never had repeatable results with comparators that have the shoulder angle in them. The Stoney Point/Hornady type with an edge contact work much better.

Good shootin' -Al

 

[RegionRat]

Unless a comparator is "zeroed" on the GoGage, then it is always just a comparator and the value is relative to whatever you set it to. User errors are common enough that I recommend rookies buy the GoGage for reference.

The bottom line is what others have shared above, the chamber is the best gage. Glad you got through it.

 

[Thaught]

Thanks everyone for the tips. I have spent hours this weekend scratching my head, measuring, remeasuring, cursing, and questioning my sanity. I consider myself a pretty competent reloader and 2nd guessing myself was not a good feeling

 

[Old Navy]

Just to spend a little more time in the reloading room, pick five new cases and measure them from bow to stern.