6 ARC Chamber Question

[MCGHeel]

Have a factory Howa mini 6 arc and new PBB prefit in 6arc on my ARC CDG action. I checked brass fired in the Howa in the PBB just out of curiosity and the bolt will not close on the fired brass. However, when I measure fired brass from the PBB and from the Howa the brass from PBB is dimensionally larger both in overall case length and base to shoulder datum. Anybody have an explanation for this? I also measured the base diameter above extractor groove and they were only .001” different there. Anywhere else I should measure? Mostly this is out of curiosity but my mind can’t make this compute just yet. Pics of brass measurements attached. Thanks

The starline brass has been trimmed after first firing in the Howa. Hornady brass hasn’t been trimmed yet after first firing from PBB.


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[43.6N]

Primers in or primers out when measuring fired brass?

Also, measure neck diameter on fired brass between the two chambers.

 

[MCGHeel]

Primers still in. Will measure neck when I get home.


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[wind gypsy]

I'm not sure which aspect in particular you are trying to compute? That it grows at shoulder and overall case length more in one barrel?

Posting the image below as an illustration of the tolerances in the SAAMI chamber spec. Noteable that the base to shoulder datum length has a 0.010" difference between min and max allowable.

 

[MCGHeel]

That’s why I’m perplexed. The shoulder datum measures one thou difference. Assuming necks aren’t so long that they’re touching lands (very unlikely I think) I’m just trying to understand why the fired case with the longer base to datum measurement will chamber fine in the PBB barrel but the shorter fired case from the Howa will not. By the way, measured neck diameter and they are exactly same between two sets of fired cases. Measured 3 per gun; all six are same measurement. Again, this is mostly a curiosity; I have 500 pieces of Peterson on the way that will be exclusively for the PBB barrel.


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[Murdy88]

I’m new to reloading but cut my teeth with the 6 arc last year. The 6ARC case has quite a lot of taper on it, so it could it be jamming further back on the case than the shoulder? You could try full length sizing without bumping the shoulder back.