Dasher initial seating depth

[Keith Glasscock]

Here is a seemingly simple task - finding the initial seating depth. Normally, you can use a fully formed case and measure the depth to touch the lands and tweak from there.

In this case, I have to do some fireforming, and I have some hydroformed brass. So here goes:

Where do you normally start? I'm using 105 VLDs for now, and I'm thinking about doing the first few shots from the barrel with a simple jam 'em and shoot 'em technique (I'm short a die right now - can't do a false shoulder). I have more than enough neck tension (new Lapua), so I was thinking about going with a seating depth that produces square marks on the bullet from the rifling.

I'm also considering the initial charge for fire forming - I'm thinking about starting at 30.5 of Varget (warm but safe in a std 6br). and working up from there. Anyone fireformed at that low of a charge? did the cases come out OK?

I know a lot of shooters here have done this, so where do you start?

 

[ShootDots]

I have a L-O-N-G story from my first Dasher... The first 25 rounds (25 of the ones I used for load development) were fireformed using the JAM method. I used "normal" 6mmBR loads... That was a GREAT mistake. I got case neck stretch and rounded shoulders. So I spoke with Donovan Moran who told me to use the "false shoulder method" >>> BUT before I did that I tried the jam method with 32.0grs of IMR 4895>>>this worked pretty well BUT I had some misfires from the case being pushed forward and not setting off the primer. I did not have NEAR enough neck tension.. Well I was not going to use that method again so I went to work with my gunsmith. We used my fired cases and his reamer came up with "about 96-97K spacer on my Dasher F/L die.. It worked perfectly! Now all I do is the false shoulder method>>>I have lost ZERO brass this way, although I am told I will eventually lose about 1-2 pieces per 100 fireformed>>>however, thus far I am fortunate that my competition cases formed with 'nary a problem! Now this is my FIRST stab at a Dasher>>>so take my words with a grain of salt. Donovan is somewhat of a Dasher "Guru" and he will gladly help you... He is DMORAN on this forum..

I hope my mistakes help you NOT to do what I did! If you MUST fireform with the jam method, I would use 3-4K neck tension, that should eliminate the problem of the bullet sliding back in the case and the case sliding forward.
But PLEASE talk with someone who has worked with a Dasher longer than I... All I can do is tell you of my mistakes and how I "fixed" them..

 

[Cigarcop]

I just formed 150 cases for my Dasher.... 30gr Varget, 3ths NT, 205 primers, with
.030 Jamb from soft touch.... I lost three that had lines on the shoulders to begin with and I knew they would split....I chambered a fireforming barrel for just this purpose as to not have to waste barrel life with my F Class rifle.

I believe its impt not to push your brass too hard while FF or its life will suffer.

 

[LRPV]

I would do the false shoulder. On the hydro formed cases, I can load a normal dasher charge that I used in fired brass into the hydro cases without issue.
Jason

 

[tclaunch]

I`ve tried both ways and prefer the false shoulder, but in your case with jamming the bullet, look for longer than wide rifling marks and especially use Federal 205 primer, this is a big one.....

 

[DMC]

+1 for what TCLaunch said

I initially used new out of box brass with 29.5 Varget with 205 primers and a 30th jam on 107 SMK's, these came out well, bumped charge up to 30.0 gr and shoulders formed better. I think neck tension would have been at least 3 th. with the new brass. these came out slightly better. The key is the hard jam and the 205 primers.
However i believe using the false shoulder method with a jam as well, would result in better cases first up
Theres plenty of very experienced Dasher shooters on here,

Safe Shooting

DMC

 

[Killshot]

Just FF'd another 50 myself yesterday; got sharp shoulders, no split necks, no misfires from the case moving forward and decent blow-lengths of 1.549".

Process: new brass run thru an expander mandrel then neck sized with a .265" bushing*, soft Winchester primers, 30.5gr Varget, 105Bergers seated .035" in from touching using Hornady's tool.

One new thing I did was to rough up the chamber of this FF-only barrel (suggested by JOHARA1) - It did result in longer blow-lengths than I had gotten with the un-roughed bore, which was my hope.

Curiosity will probably cause me to try the false shoulder method eventually but I have gotten good results on target with my simple way.

* have a no-turn .2704" neck