338 RCM headspace gauges

[atl5029]

My gunsmith who is doing the rebarrel work for my 16.5" 338 RCM I posted about earlier is having a really hard time finding headspace gauges to rent for this job. Would anyone who has 338 RCM go and no go gauges be kind enough to let me borrow them for this one job. Or does anyone know where I might be able to find them to buy, rent, or borrow in short order?

Alternatively, I do have new, unfired brass and dies. Can a barrel be properly headspaced off of a new piece of brass? Or should I FL size a new piece first?

Thanks all for your help

 

[PusherX11]

Have you or your smith found a set of gauges? I have a set in route from PTG.

 

[atl5029]

Have you or your smith found a set of gauges? I have a set in route from PTG.

We did eventually find some. Thanks

 

[Ray Gross]

It is not obvious because they have different datums, but if you were to convert the 338 RCM headspace length to a .420 datum, it is within .0001 of the 6.5 PRC. The chamber body diameters and shoulder angles are the same. The 6.5 PRC is quite literally a necked down 338 RCM.

338 RCM SAAMI headspace is 1.6227 to .450 datum, converted to a .420 datum it is 1.648681

6.5 PRC SAAMI headspace is 1.6486 to .420 Datum

The .000081 difference is well inside gage manufacturing tolerances. IOW, you can use 6.5 PRC gages to headspace the 338 RCM.