A gunsmith question - head spacing.

I have a wee dilemma, I think I might understand the problem but would like some expert advice. Have a standard factory REM SA along with a standard REM factory bbl in 260 cal (new or near new) bought bbl from some one on here a while back. So sent off to get bbl attached to action via local gunshop. Also provided a unfired brass Lapua case for headspacing. Msg back from gunshop says “smith needs a 260 reamer to do the head spacing”. Hence my post asking if anyone has a reamer I could buy or borrow.
So why would a reamer be needed when you’ve got a standard factory action & bolt, and standard factory bbl chambered in 260 ?
I guess that within tolerances for action, bolt and bbl chamber you might end up with slightly undersize headspace once bbl is screwed in fully ? Hence need to ream chamber deeper by a couple of thou ? Am I on the right track ? Or would there be other reasons for needing reamer ? And, if I can’t locate a 260 reamer, are there other options ? Would a 243 reamer work ?

https://www.brownells.com/tools-clea...?sku=184050215

Thanks, trying to avoid the import hassle if possible

Not sure a reamer would pose any hassle?

Maybe had to trim a bit off chamber end for some reason. Did you ask guy thats doing it?

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Originally Posted by blip

Maybe had to trim a bit off chamber end for some reason. Did you ask guy thats doing it?

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Yes, via the gunshop. No details back as yet.

Just send it my way mate. I still owe you a favour.

To answer your question. Its all about quality and manufacturing. Remington actions are not manufactured to the same quality as a custom action is for example.

Why is a reamer needed? If the headspacing is to big or short the smith will need a reamer to correct it. To long: Your cases will stretch and be destroyed, to short and the cartridges wouldn't fit.

Between us: if anyone, especially a gunsmith wants to do head spacing using a case - get you rifle away from them.

Yea so imagine that you screwed the barrel in tight, then the headspace was too short.
You'd need to run a reamer through it to extend chamber to the correct length.

Or if headspace was too long, then I guess you'd machine a couple threads off the barrel so when it was screwed in tight, the headspace is correct. (not a gunsmith)

Eitherway the headspace should be determined by the go/nogo gauge instead of a vergin brass...

Other solution, is fitting a custom recoil lug , slightly thicker. The benefit is that a bit of truing work can be done on the action face, bolt face and lug abutment/ contact if required . Final Headspace adjustment is then done by surface grinding the extra lug thickness or removing material from barrel shoulder. Proper go gauge is a must have. The only issue with that method is that you can not really time the barrel properly to have the writing where it should be.

Thanks- Not too worried about the timing, can always get a new set of “260 cal” numbers stamped if need be.