Neck tension, bushing choice, and runout

[Aaron47pb]

So I am getting into the 6 Dasher and I am fireforming Lapua 6BR brass. The necks of loaded rounds are measuring "0.268. So it looks like I'll need to use the 0.267" bushing (or even 0.266"). But necks of fired cases are measuring 0.271".

I've been told/and read that going down 0.004" in a single step and cause runout.

Here is my question. In practice, how much does the runout induced from going down 0.004" in a single step actually matter?

I am not shooting BR matches. Just looking for 1/2 MOA. I don't enjoy reloading and would like to keep sizing to a single step if possible. I will probably try it and see for myself, but I'm just curious if anyone can share their experience going down 0.004" in one step.

Thanks!

 

[just browsing]

I use a .267 bushing with Lapua brass and it gives me .001-ish NT. It’s definitely on the light side so if you think you’ll end up loading your bullets long or into the lands I would go .266.

Regarding run-out (or avoiding it), I would recommend fireforming your brass with a false shoulder. I used a .264 expander mandrel to neck it up and then back down with the Dasher dies. It’s an extra step the first time, but I’ve found this process to produce noticeably better case neck uniformity and overall case life as opposed to “jam-forming.” Once the case is formed, I anneal every other firing with a light chamfer and debur. Otherwise, no neck turning, trimming, or anything crazy is needed. Just load and shoot.

YMMV, but it sounds like you have a good starting point. Good luck.

 

[dave300]

I feel your pain, in short, .003 is the max I go at a time before I notice that an excessive amount of runout is introduced. I spent way to much time trying to correct it and just came to the conclusion that I was going to have to neck size in two steps.
Having said that, give what your trying a chance and see if they shoot. Brass type and annealing do have a significant impact on how big of a step you can get away with?

 

[spife7980]

Sure your necks dont measure .269? Thats what Ive always read they measure and thats what mine measure that I just built for this year are.

Youll be just fine with a bushing sizing it from .271 to .265 at least.
If you want to skip expanding and only size down then get a .267 bushing (or .266 if they really are a thou thinner)
If you want to run an expander get .265 bushing.