Hornady Headspace Comparator & Bushings

[Charlie-NY]

I've got a Hornady Headspace gauge and the 5 bushing for the gauge. The 6mm BR uses the .350" bushing but there is no listing for the 6mm Dasher. I assume it uses a different bushing.
Does anyone know the correct bushing for the Dasher?

 

[rijndael]

.375" Note the dimension on the reamer print:

 

[Charlie-NY]

.375" Note the dimension on the reamer print:

View attachment 1592235

Thank you - I'm just getting started with a Dasher and rely on the Hornady Headspace tool.

 

[rwj]

If possible, have the smith that chambers the barrel make you a stub gauge using the same reamer. Best to measure headspace using a full profile that replicates the chamber than a comparator that only has line contact on the shoulder.

 

[JFrank]

I use a .30 cal bushing as a headspace comparator for 6 br or 6 br-a. It doesn’t really matter.

 

[PatMiles]

I use a .30 cal bushing as a headspace comparator for 6 br or 6 br-a. It doesn’t really matter.

It doesn't matter as long as you use the same bushing EVERY time you measure headspace.

 

[Will Henry]

If possible, have the smith that chambers the barrel make you a stub gauge using the same reamer. Best to measure headspace using a full profile that replicates the chamber than a comparator that only has line contact on the shoulder.

This is true if the angle on the shoulder of the gauge is precisely the same as shoulder of the chamber. If it is not, the datum will not contact. The difference would be minute but there, nonetheless. WH

 

[rwj]

This is true if the angle on the shoulder of the gauge is precisely the same as shoulder of the chamber. If it is not, the datum will not contact. The difference would be minute but there, nonetheless. WH

How could the shoulder angles differ if the gauge and chamber are formed using the same reamer?

 

[Will Henry]

The gauge isn't formed using a reamer. It is ground. Now presumedly it is ground on the same setting as the reamer so the angles are precisely the same, but I don't know that. For all I know, the companies may not use the same grinder (it would make sense that they wouldn't) In addition, if the reamer is ground by one company and the gauge by another, you are at the mercy of tolerances accepted by both. The reality is, any difference is as I said, minute, but it can exist. If all the gauge is doing is providing comparative measurements, it doesn't really matter. In addition, headspace gauges are not generally used to measure to .0001".
The use of a datum line to measure a taper is established common practice. It works. WH

 

[rwj]

The gauge isn't formed using a reamer. It is ground. Now presumedly it is ground on the same setting as the reamer so the angles are precisely the same, but I don't know that. For all I know, the companies may not use the same grinder (it would make sense that they wouldn't) In addition, if the reamer is ground by one company and the gauge by another, you are at the mercy of tolerances accepted by both. The reality is, any difference is as I said, minute, but it can exist. If all the gauge is doing is providing comparative measurements, it doesn't really matter. In addition, headspace gauges are not generally used to measure to .0001".
The use of a datum line to measure a taper is established common practice. It works. WH

The gauges I have were made by the smith that did the chambering using my reamer on a stub section cut from the barrel. No grinding involved.

 

[JFrank]

It doesn't matter as long as you use the same bushing EVERY time you measure headspace.

Great point, I’ll also mention for new readers that i had a hell of a time when I first started reloading for precision because I was so worried about getting the exact .002 shoulder bump and navigating through all the input from fellas. The bottom line is to have brass that cycles freely before and AFTER ignition and if that takes .003 or .0025 then so be it. A guy may have to adjust the die a wee bit when setting up and forming brass until we get comfortable with the results.
Nothing worse than fighting a bolt open during a record string of fire.

Jim

 

[Will Henry]

The gauges I have were made by the smith that did the chambering using my reamer on a stub section cut from the barrel. No grinding involved.

My mistake. We are speaking about different gauges altogether. Your gauge is for measuring the case. I was thinking of gauge for measuring the chamber. This may be evidence of cognitive decline on my part! WH

 

[rwj]

We are speaking about different gauges altogether. Your gauge is for measuring the case. I was thinking of gauge for measuring the chamber.

Bingo… I had the same thought not long before your last post!