I need to give back to the site... everyone here has been incredibly helpful so I figured I would post a detailed step by step on false shouldering for the 6 dasher fireforming newbies (like me). It's intimidating if you have never done it.
Specs:
26 inch bartlein barrel
1.555 chamber
272 no-turn neck
104 freebore
Defiance Deviant action
Start with Lapua blue box 6BR norma brass
Steps
1) Size up the neck: I used a 21st century expander mandrel die with the 264 expander mandrel
264 expander mandrel bought from Sinclair (not the turning mandrel FYI which is 0.001 different). Used imperial sizing wax, don't just use dry neck lube that stuff sucks.
2) Next make the false shoulder: Forster full length sizing 6mm Dasher die WITH DECAPPING ASSEMBLY REMOVED. This will require quite a few back and forth trials with your rifle. What I ended up doing was looking for the point where I had a decent amount of resistance the ENTIRE time when you close the bolt, and it should get harder right at the end. Dmoran calls this a "full crush"
Important to note when you remove the decapping assembly (not everyone does this), the neck size will be super tight (.253"), so I ended up re-expanding with a 243 sinclair mandrel (note .2675 is what 6BR brass comes as out of the box in my lot #). ALSO MUSHROOMING is NORMAL after making the false shoulder (see brass on right). Note, re-expanding with a 243 mandrel makes the mushroom go away (see brass on left)
For me, I ended up making the false shoulder, then re-expand w/ the 243 mandrel until I achieved the full crush. It should take a decent amount of force to close, I would say 30-40% more effort to close the bolt on a regular basis. Also I wiped off all the sizing wax everytime I chambered the rifle.
There are threads on this forum about making sure the chamber is oil free/dry to reach optimal blow length (more on this below).
3) Next step, double check your work with an actual projectile... I would highly recommend this before you load 250 rounds to fire form. I'm glad I did this b/c when I seated the bullet with a forster micrometer seater die in 6 dasher, it was VERY hard to close the bolt (75% more effort then normally trying to close a bolt). So the false shoulder expanded every so slightly from 0.2880 to 0.2885-0.2890 after seating a bullet. So I had turn in the Forster FLS die I used to make the false shoulder a hair clockwise, re-expanded with 243 mandrel, seated the bullet and voila! Back to 30-40% more effort with a full crush to close the bolt when the projectile was seated... (this was all along with the pin pulled and ejector removed, but extractor intact).
I seated 0.020" into the lands for good measure, Varget 30gr w/ a hornady 105 amax (lots of combos out there; but, this one appears to be a "standard" powder charge) results in 1.532-1.536 blow lengths, most being 1.532-1.534... I tried cleaning the bore & chamber every 5 rounds, 20 rounds, and 50 rounds and degreased it with rubbing alcohol at the end; but, this made absolutely no difference in my blow lengths. However, I am of the school of thought that it doesn't really matter for accuracy (see my results).
Right is a virgin 6BR brass, middle is a perfect blown out 6 dasher brass, left is what you will see every once in awhile. I had 4 of these split necks in the 300 rounds I fire-formed.
I got around to doing load development (finally) on this 1 x fired brass, with just a light inside and out chamfer after I sized with a whidden FLS bushing die 267 RCBS nitride bushing w/ the expander ball in.
Load is with Varget and Berger 105 hybrids. This is with 250 fire formed rounds on the barrel.
Top row is the OCW 32.3, 32.6,32.9, 33.0, 33.2 (seated 0.015 off lands), and 32.6 (seated 0.020 off lands which was a go to load from well known precision tactical shooters).
32.6 gr of Varget = 2978 fps (on average) SD 4.2
33.0 gr of Varget = 3006 fps (on average) SD 5.4
NO PRESSURE SIGNS AT ALL! 3 round groups. Shot off the bench... pretty much all loads though were 1/2 MOA or less which was insane.
I'm going with 33.0 gr based on not only group size, gunsmith who chambered this that's his load too with this reamer, and it happened to be within the middle of the node ( i know it's not so obvious in this picture)
In summary, false shouldering isn't that much more time, it yielded good results, it is intimidating at first; but, it's worth the effort.... "just do it". Blow length wasn't great for me; but, oh well, still darn accurate. I absolutely LOVE THE 6 Dasher, and you will too!!!
Specs:
26 inch bartlein barrel
1.555 chamber
272 no-turn neck
104 freebore
Defiance Deviant action
Start with Lapua blue box 6BR norma brass
Steps
1) Size up the neck: I used a 21st century expander mandrel die with the 264 expander mandrel
264 expander mandrel bought from Sinclair (not the turning mandrel FYI which is 0.001 different). Used imperial sizing wax, don't just use dry neck lube that stuff sucks.
2) Next make the false shoulder: Forster full length sizing 6mm Dasher die WITH DECAPPING ASSEMBLY REMOVED. This will require quite a few back and forth trials with your rifle. What I ended up doing was looking for the point where I had a decent amount of resistance the ENTIRE time when you close the bolt, and it should get harder right at the end. Dmoran calls this a "full crush"
Important to note when you remove the decapping assembly (not everyone does this), the neck size will be super tight (.253"), so I ended up re-expanding with a 243 sinclair mandrel (note .2675 is what 6BR brass comes as out of the box in my lot #). ALSO MUSHROOMING is NORMAL after making the false shoulder (see brass on right). Note, re-expanding with a 243 mandrel makes the mushroom go away (see brass on left)
For me, I ended up making the false shoulder, then re-expand w/ the 243 mandrel until I achieved the full crush. It should take a decent amount of force to close, I would say 30-40% more effort to close the bolt on a regular basis. Also I wiped off all the sizing wax everytime I chambered the rifle.
There are threads on this forum about making sure the chamber is oil free/dry to reach optimal blow length (more on this below).
3) Next step, double check your work with an actual projectile... I would highly recommend this before you load 250 rounds to fire form. I'm glad I did this b/c when I seated the bullet with a forster micrometer seater die in 6 dasher, it was VERY hard to close the bolt (75% more effort then normally trying to close a bolt). So the false shoulder expanded every so slightly from 0.2880 to 0.2885-0.2890 after seating a bullet. So I had turn in the Forster FLS die I used to make the false shoulder a hair clockwise, re-expanded with 243 mandrel, seated the bullet and voila! Back to 30-40% more effort with a full crush to close the bolt when the projectile was seated... (this was all along with the pin pulled and ejector removed, but extractor intact).
I seated 0.020" into the lands for good measure, Varget 30gr w/ a hornady 105 amax (lots of combos out there; but, this one appears to be a "standard" powder charge) results in 1.532-1.536 blow lengths, most being 1.532-1.534... I tried cleaning the bore & chamber every 5 rounds, 20 rounds, and 50 rounds and degreased it with rubbing alcohol at the end; but, this made absolutely no difference in my blow lengths. However, I am of the school of thought that it doesn't really matter for accuracy (see my results).
Right is a virgin 6BR brass, middle is a perfect blown out 6 dasher brass, left is what you will see every once in awhile. I had 4 of these split necks in the 300 rounds I fire-formed.
I got around to doing load development (finally) on this 1 x fired brass, with just a light inside and out chamfer after I sized with a whidden FLS bushing die 267 RCBS nitride bushing w/ the expander ball in.
Load is with Varget and Berger 105 hybrids. This is with 250 fire formed rounds on the barrel.
Top row is the OCW 32.3, 32.6,32.9, 33.0, 33.2 (seated 0.015 off lands), and 32.6 (seated 0.020 off lands which was a go to load from well known precision tactical shooters).
32.6 gr of Varget = 2978 fps (on average) SD 4.2
33.0 gr of Varget = 3006 fps (on average) SD 5.4
NO PRESSURE SIGNS AT ALL! 3 round groups. Shot off the bench... pretty much all loads though were 1/2 MOA or less which was insane.
I'm going with 33.0 gr based on not only group size, gunsmith who chambered this that's his load too with this reamer, and it happened to be within the middle of the node ( i know it's not so obvious in this picture)
In summary, false shouldering isn't that much more time, it yielded good results, it is intimidating at first; but, it's worth the effort.... "just do it". Blow length wasn't great for me; but, oh well, still darn accurate. I absolutely LOVE THE 6 Dasher, and you will too!!!
Last edited:
Knock on wood, but I’ve never had an issue forming brass on any wildcats with Dasher type improved shoulders by jamming the bullets and firing away. Always very accurate during the forming process as well. Actually had one wildcat that I later struggled hard in load testing to match the accuracy of initial forming rounds.
