Trim length for BR to fireform to dasher

[Cody Richardson]

What length should I be trimming BR to that I’m fireforming into dasher. .272 neck so I’m trimming to length, turning the neck to create a false shoulder and then fireforming.

 

[savagedasher]

I haven’t ever had to trim
I don’t use the false should also
I like flat bass bullets jamming

 

[dmoran]

Likely your chamber is long enough to not need to trim the brass before fire-forming (but do need to make sure of this).
Do you have a blue-print of the reamer used, or access to one?
If so, it will tell you the length of the chamber.

Unless you worded it wrong of your planned process, and your chamber neck diameter is .272", it is to large to false-shoulder off a neck cut. You will have to create a false shoulder by expansion of the neck and partially sizing part of it back down (attaching a picture below).

It has been my experience, the false-shoulder method forms the most consistent cases to lengths and capacities.

Myself do no trimming until they have been fired at least twice, then by trimming the longest ones to the shortest ones lengths.
I also qualify the lengths before doing so, cuing out any extremes (shorts).


In the picture below:
1. Neck turned to the shoulder junction.
2. Expanded the necks with a .264" mandrel.
3. Partial neck sized back down with a bushing neck die (can be done with a F/L die as well).
4. Suggest at least .020" of crush to the false-shoulder on bolt closer.

 

[drags]

Likely your chamber is long enough to not need to trim the brass (but you will need to make sure of this).
Do you have a blue-print of the reamer used, or access to one?
If so, it will tell you if the length of the chamber.

Unless you worded it wrong of your planned process, and your chamber neck diameter is .272", it is to large to false-shoulder off a neck cut. You will have to create a false shoulder by expansion of the neck and partially sizing part of it back down (attaching a picture below).

It has been my experience, the false-shoulder method forms the most consistent cases to lengths and capacities.

Myself do no trimming until they have been fired at least twice, then by trimming the longest ones to the shortest ones lengths.
I also qualify the lengths before doing so, cuing out any extremes (shorts).


In the picture below:
1. Neck turned to the shoulder junction.
2. Expanded the necks with a .264" mandrel.
3. Partial neck sized back down with a bushing neck die (can be done with a F/L die as well).
4. Suggest at least .020" of crush to the false-shoulder on bolt closer.
Hi dmoran, I do everything that you have described here except turning down to the shoulder junction, I turn just far enough down the neck so that the turned part of the neck goes in to the shoulder after fire forming. Why do you turn into the shoulder junction?

View attachment 1084381

 

[dmoran]

@drags
To eliminate donut/taper issues as the brass flows forward as it is cycled, by blowing/forming the cutter stop point well into the shoulder.
(example below)