Shoulder dimensions and chamber size questions before threading on a new barrel

[EchoDeltaSierra]

Considering the below measurements, are there advantages to thread barrel onto and action producing a smaller or larger chamber?

One could snug the barrel to the go gauge and make the chamber smaller at 1.536-1.537 or one could set it to the edge of the no-go gauge and have a 1.540-1.541 chamber. Also, this might be an irrelevant matter but my theory is that a larger chamber might allow a hotter load and a smaller might be easier on brass. Curious about thoughts / feedback.

Load: 6.5CR shoulder measurements (all taken today with the same comparator)
- Fireformed Lapua Brass: 1.539" (formed in the chamber of my current Remington 700 action/barrel)
- Hornady Precision Hunter: 1.534"
- Mason chamber gauges:
-- Go: 1.536"
-- No-Go: 1.542"

 

[spife7980]

Once your brass is formed I don’t think there will be that much difference.

Your fireformed brass is right in between what your gauges measure so I would call that just about perfect.

 

[EchoDeltaSierra]

The fire-formed dimension above is from my existing Remington 700 5R barreled action. I’m wondering where I should headspace a new Nucleus action/Criterion barrel; or if this detail even matters.

 

[memilanuk]

About the only meaningful difference is going to be whether or not other people's ammo works in your gun. The tighter your headspace, the less chance that their sized brass is going to fit in your chamber.

We went through all sorts of B.S. with this for the 2017 FCWC for F/TR... the official GO/NO-GO gauges designed by the sanctioning body (ICFRA) didn't jive with the ones commercially available in the USA (or probably anywhere), so there were some people scrambling to have the headspace tweaked on their rifles. Me, I ended up with a very nice set of Forster 'National Match' headspace gauges for .308 Win, which has every size from 1.630 to 1.638, in 0.001" increments. Set mine to close on 1.631", not close on 1.632", and was good to go. And yes, they did check

Otherwise... you'd probably pick up more 'performance' by finding a brass that weighs less and has more internal volume - or just going with small primer brass and treat 'em as 'consumables'

 

[918v]

An increase in shoulder length won’t increase case volume like an increase in shoulder/base diameter will.

 

[Supersubes]

I’d erase all thoughts of trying to increase performance by increasing headspace. It’s just not a practical matter. For comparison, look at a 6.5x47 and a creedmoor. They run near identically once tuned up. Same shoulder diameter and base diameter, but the 47 shoulder is about .080” shorter. Your .003-.004 will mean absolutely nothing.

I set up my chambers to be minimum on my unfired brass. If I was to go longer, I’d set them up to touch or a c-hair bigger on a GO gauge.

 

[EchoDeltaSierra]

I’d set them up to touch or a c-hair bigger on a GO gauge.

Do you have a micrometer reference measurement? Also, does color matter?

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