Fireform 6mm Dasher Questions...

[alf]

I have fire-formed several thousand Dasher cases with the false shoulder method.

First, by necking up with Sinclair's 25 cal mandrel, then necking back down with a .267 bushing in a full length die, and fire-forming with a stout load.

I've found cases need to be shot a second time to get any meaningful results in load development.

If you're dedicated to shooting a Dasher, I'd get a slave barrel chambered with a no-turn reamer and blow your brass out straight in that barrel first, then do your brass detailing for the match barrel.

Al

 

[PEI Rob]

So you are saying that you get much better results from actualy FF your brass with full on loads than you do when forming cases with the hydraulic form die??. ...

Yes. Hydraulically formed brass has very rounded shoulders. The neck to shoulder junction is nice and that is what I liked. Headspace is perfect due to the nice job at the neck/shoulder junction and partial shoulder. When you use full house loads obviously the case is now perfectly shaped.

When I tried expanding the shoulders with several highly polished tapered expanders, I found it caused some runout. The runout became unacceptable when I sized the neck back down, the tolerances seemed to stack up. Also, I found the "false shoulder" on the neck inconsistant in respect to headspace. Sometimes the bolt was very hard to close and some were way too easy. Jamming the bullet hard into the lands with lots of neck tension just made the bolt hard to close everytime. It surely doesn't stop the case from moving forwards when the firing pin hits the primer. Kill a primer and try it.

I did not put much effort into the false shoulder method and cannot say it doesn't work. I can say it didn't work the way I was trying it. When I tried the hydraulic method, I noticed the nice sharp neck/shoulder junction at the perfect location and of course zero runout. Pressure when closing the bolt was extremely consistant and the firing pin was not going to move the case now.

If I could have gotten the false shoulder method to work I would definately go that route.

As far as accuracy goes, it wasn't good until I used a full house load then trimmed.