Befuddled, please enlighten me - Headspace Guage

[ToolMann]

Alright guys, I'm completely befuddled here. I finally bought the Hornady headspace bushings as I'm working loads for my wife's new rifle. Never cared a ton about "bump" as I'm not a bench shooter and don't shoot a ton. But, I like nerding out and figured I'd play with the sizing die. But I'm getting equal or longer measurements on new/unfired/unsized brass when compared to fired brass. How is this possible? I admit I don't have the best set of calipers and if I push hard I can flex .001 to .002 out of it, but I'm being very careful and have measured a bunch of each for comparison. I'm seeing a .003ish bump on my sized brass, but have no idea how unfired brass can have more distance to the should than fired/unsized brass. Is it possible the shoulder angle changes and on the fired brass and the bushing is landing lower on the shoulder? Not sure it matters a ton as the comparison I'm looking for should be between fired/unsized and sized, but I'm losing my mind here. Any information that will help my brain slow down so I can sleep tonight would be appreciated.

TM

 

[Dos XX]

You could have a tightly headspaced chamber. The unfired brass might be right at the chamber dimension. When fired, it can form to chamber then have bounce back. Can you feel resistance when closing the bolt on a new piece of brass? You might have to strip your bolt to really tell. I have had new brass that would be crush fit, or maybe a light crush fit.

 

[ToolMann]

You could have a tightly headspaced chamber. The unfired brass might be right at the chamber dimension. When fired, it can form to chamber then have bounce back. Can you feel resistance when closing the bolt on a new piece of brass? You might have to strip your bolt to really tell. I have had new brass that would be crush fit, or maybe a light crush fit.

That is a good question and already opening my mind a bit. I had heard that unfired/unsized brass was the smallest it would probably ever be. I full length sized the new brass before loading, but never tried chambering a piece of the new brass before sizing. I sort of forgot about the sizing before loading step and couldn't fathom how brass would get "shorter" after firing, but it was never fired at the long length since I sized before loading. I'll try chambering a piece of the new/unsized brass in the morning. Thanks!

For reference, if it matter in this discussion, it is a Tikka T3X Super Lite in 7mm-08.

TM

 

[Dos XX]

Tikka bolts are easy to strip.

Also, it is possible to make brass longer when you size it if you do not have the die adjusted far enough to move the shoulder. It kind of squeezes it forward.

 

[ToolMann]

Tikka bolts are easy to strip.

Also, it is possible to make brass longer when you size it if you do not have the die adjusted far enough to move the shoulder. It kind of squeezes it forward.

Is the "easy to strip" comment geared towards stripping the bolt and checking for bolt closure force without the firing pin?

The seating die is definitely shortening the brass at the shoulder. The sized brass are shorter than the fired/non-sized and unfired/unsized brass.

 

[Dos XX]

Is the "easy to strip" comment geared towards stripping the bolt and checking for bolt closure force without the firing pin?

Yes and without the ejector.

You may be able to tell without stripping the bolt. It depends on how tight a fit it is. Compare a bumped to an unfired unsized piece without stripping bolt and see what you feel.

 

[Vern400]

You should be aiming for 0.002 or 0.003 shoulder clearance when you close the bolt. To do that, ideally you need to find a piece of brass that closes with a very snug to tight bolt. Measure it and write down that number. It should not change. You back off THAT number 2 thousandths and CHECK IT for easy bolt closure. Your dies can cram the shoulder way back, which can cause stretching and ultimately case separation. If you jam your dies down to the shell holder that's probably happening.

This brass, that brass, new, used, what the dimension really is ..... Largely aren't so important.

I have 2 rifles identical but headspace differs by 2 or 3 thousandths. I let the brass get mixed up and learned the hard way. Loaded hundreds of premium cartridges and some are too tight to close. (Shoot them in the longer chamber only)
What a nuisance!

 

[ToolMann]

You should be aiming for 0.002 or 0.003 shoulder clearance when you close the bolt. To do that, ideally you need to find a piece of brass that closes with a very snug to tight bolt. Measure it and write down that number. It should not change. You back off THAT number 2 thousandths and CHECK IT for easy bolt closure. Your dies can cram the shoulder way back, which can cause stretching and ultimately case separation. If you jam your dies down to the shell holder that's probably happening.

This brass, that brass, new, used, what the dimension really is ..... Largely aren't so important.

I have 2 rifles identical but headspace differs by 2 or 3 thousandths. I let the brass get mixed up and learned the hard way. Loaded hundreds of premium cartridges and some are too tight to close. (Shoot them in the longer chamber only)
What a nuisance!

Thanks. It is my understanding that the case you use are your base measurement which you would then bump .002 to .003 down from, is a case fired from the chamber you are loading for, as that brass will have expanded to fill the head space when it was fired. It is currently bumping .004 to .005, so I'm going to adjust the sizing die a bit.

I don't have multiple rifles of a single caliber, so no chance of mixing brass from different rifles.

TM

 

[Vern400]

Thanks. It is my understanding that the case you use are your base measurement which you would then bump .002 to .003 down from, is a case fired from the chamber you are loading for, as that brass will have expanded to fill the head space when it was fired. It is currently bumping .004 to .005, so I'm going to adjust the sizing die a bit.

I don't have multiple rifles of a single caliber, so no chance of mixing brass from different rifles.

TM

Yes but hopefully you can find one that has tight or snug bolt lift. THEN you know you have a contact fit to zero from. I neck sized for years before I learned better ways and never pushed back the shoulder with zero issues.

So the best reference is" bolt closes with mild resistance.
The best reference is NOT "well, I shot it in my gun".

I tend to run high end loads in 308. Still never FL sized until I mixed brass.

 

[ToolMann]

Yes but hopefully you can find one that has tight or snug bolt lift. THEN you know you have a contact fit to zero from. I neck sized for years before I learned better ways and never pushed back the shoulder with zero issues.

So the best reference is" bolt closes with mild resistance.
The best reference is NOT "well, I shot it in my gun".

I tend to run high end loads in 308. Still never FL sized until I mixed brass.

Thanks!

 

[rayporter]

it will take 2 shots and sometimes 3 shots for a case to 'fill' the chamber,

 

[Axlrod]

The best way to size brass is with a striped bolt. You my not have to bump the shoulder back for several firings. Go down to the "sizing brass" video on this link. It explains it very well. There is also a very good video on finding your lands- for bullet seating.

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