View Full Version : 6mm Dasher Fire Forming Questions

12-06-2014, 03:00 PM
I am having a 6mm Dasher built for LR Prone, and have gathered some new Blue Box Lapua 6mm BR cases. I have read several posts regarding ways that one can fire form this brass into a Dasher. I am an experienced shooter and reloader, but have never fire formed cases.
I have a few questions, my chamber is a no-turn neck and have been thinking about using the COW method of forming, basically to save on barrel life. I am aware that straight jamming of a 107 SMK under a stout load of RE-15 or whatever has been successful as well as false shouldering and firing 107 SMK's jammed or not. Also, I know that these methods are not perfect and case movement is noted, which can result in the round not firing.

If I were use COW, after forming a false shoulder, necking ~ 1/2 of the neck back to 6mm and utilizing Unique or some other fast pistol powder, what else, besides firing a real load after COWing is necessary to get a good Dasher case? I have read in places that the dreaded donut can occur, is this always and how is that delt with or does that occur only when necks are turned prior to fire forming?

If anyone can fill in the blanks on these questions, it is appreciated. Any other info on the Dasher is welcome too.



12-06-2014, 05:34 PM

There is a boat load of Dasher info over on the Accuateshooter forum.


12-07-2014, 08:43 PM
Neck them up to 7mm then size them back down with the Dasher die, or you can just jam the bullet if you have mucho neck tension.

12-08-2014, 04:01 PM
Explain to me how you will get a donut, when the shoulder will be formed with half of the neck that is the same thickness……… If you turn necks, stop neck turner for the shoulder. Blow length is important, so listen up long seat a bullet with a bunch of neck tension plus a the shoulder you form with the cutter or a false shoulder. I prefer Varget for fire forming and a heavy bullet that will back up the shoulder you formed. Use a soft primer like a Federal, clean and dry the chamber and a loaded round. I prefer a 115 but a 108 will work, with 30.0 gr. of Varget and fire it, measure it if it's short increase the load to 30.5 and keep going till you hit the length.of 1.550 to 1.553. Never let the barrel get hot and clean the chamber and rounds off with non chlorinated brake cleaner, YOU WANT NO LUBE in the chamber or on the case or they will be short, If they come out longer you are stretching the case because your shoulder isn't holding it back and they are junk. You will hear BS. about putting oil on them but don't believe it………. I make mine in the winter and just shoot them in the dirt breaking in barrels or with a FF. barrel. If by some chance they are short your chamber is too polished…… i have a fix for that also……. If you do it right they will last a long time, Cow method and the hydro forming they will be short, and a Dasher doesn't grow, they will one time after fire forming and if they are short, they stay short unless create head space. I may trim once or twice a year……… jim