Gunsmithing Funky Headspace issues

[waste_knot]

Received a new Forster 308 (go) headspace gauge marked 1.630. My problem may be from the Hornady headspace comparator I use for measuring brass. The Forster gauge measures 1.620 with the comparator which is measuring from the base to a ring of 0.400 on the Forster gauge. Does anybody else use a Hornady comparator? What is the diameter of the ring bore? Mine measures .400 but I think its been bored out.

 

[skinnj1]

Re: Funky Headspace issues

It seems like you are confusing the intent of both gauges, one (forester) is made to exacting tolerances envolving cylindrical grinding of tool steel to the industry (saami) dimensions and the other is simply a drilled/bored/reamed hole in al. The hornady gauge is realy meant for making relative measurements ie measure your fired brass and use to adjust dies .002 etc.


Totally diferent tools with different purposes even though both measure headspace

 

[waste_knot]

Re: Funky Headspace issues

How would I know if the Forster is ground wrong or short?
SAAMI chamber print says 308 headspace is the distance from the bolt face to a datum ring in the chamber .400 dia. I'm I reading the print wrong or is the .400 not a MMC dimension?

 

[skinnj1]

Re: Funky Headspace issues

Unless you have an optical comparator like the people who grind reamers and gauges i would ASSUME it is right. What i would reccomend doing is using electronic calipers and zeroing the setup on the headspace gauge, now you can take a relative measurement to saami minimum but even this is unneccesary for what the stoney point / hornady gauge was meant for,adjusting your dies...what do you want to do with each gauge

 

[tipper]

Re: Funky Headspace issues

Yes my Hornady headspace comparator D-400 measures 1.620 on my PTG 308 go-gauge

 

[alton]

Re: Funky Headspace issues

Mine also measures 0.400.

 

[waste_knot]

Re: Funky Headspace issues

Thanks Guys. I turned a new D400 on the lathe and bored it to 0.395. It now makes the headspace gauge read the correct length. I now realize the Hornady was measuring the new brass (win & Lapua)short at 1.625. Now it measures 1.629 so there is 001 to 002 of headspace.

 

[2156SMK]

Re: Funky Headspace issues

While the BORE of the hornady measuring tool probably measures 0.400", I would bet there is a chamfer in there and the actual measurement you get was getting was being effected by the 0.010".

As everyone else said, the Hornady tool is for incremental measurements, not absolute measurements...