Seating depth test while forming Ackley brass?

[Fast14riot]

Would there be any issue with results from testing seating depth for a certain bullet while fire forming 260 Ackley brass, with intentions of using that length for the final formed cases?

 

[JLT]

I've not encountered any issues with the practice. That's exactly what I do when I fire form AI brass and I've never had the formed cases tell me different.

 

[ImBIllT]

In theory it should work just fine. That's because Ackley chambers should be set up to have a slight crush on the patent cartridge at the neck/shoulder junction. I usually jam everything just in case there is a little slop. If you wanna be sure, you can pull the firing pin, and ejector spring close the bolt with nothing in the chamber and close the bolt with an unfired case in the chamber. If the case causes some resistance in closure, then there is no need to jam during fire forming, so feel free to test seating depths.

 

[Fast14riot]

Logically it made sense to me as seating depth tests are largely independent of charge weight. I've seated everything right now to jam .008", I can just run through the seating die and do my test. Just wanted to be sure there wasn't something I was missing. Thanks.

 

[mikecr]

I've convinced myself through testing that best seating depth has nothing to do with powder. So I do a full test(similar to Berger's recommended) while fire forming cases. Then, with fully formed cases & what I call 'best coarse seating' I move to powder with ladder testing. Then, with best powder, I tweak seating just a smidge each way to shape grouping nice & tight, and define my seating window.
If best seating is off the lands(OTL), I will never have to mess with it again for the life of that barrel, even with powder/load/tension changes.

 

[dmoran]

Two question:

Q1. - Say you want to test a .050" range of seating.
Would you consider two loads with .050" variation in seating the same load? (particularly by pressure?)

Q2. - Would you consider a case fire-formed with say a 55,000-psi load to be of equality to a case that is fire-formed with say a 57,000-psi load?

My own input; would expect the pressure/velocity to be different at each increment in seating depths being tested (and depending on the extent of variation in seating, possibly even substantial pressure indifference).
When I fire-form I want equality in blow lengths and diameters from the blow so that the volumes also end up uniform. In my experience the loads pressures need to be the same to get consistency and equality to case lengths, diameters, and capacities when fire-forming.
Donovan

 

[mikecr]

It takes at least 2 firings to be fully fire formed(even with deep body dip annealing). The second firing can be consistent as you like with higher pressure and no other testing.

 

[dmoran]

@mikecr
In my own experience, the 1st fire-forming hit is when the majority of stretching, shaping, and forming will occur. Which is the most critical time for consistency from case to case, with far less brass flow occurring on the 2nd & 3rd hits, and far less measurable amounts.

IME - if they blow short, they will remain short (with less capacity), and visa versa (my experience is primarily based on 6PPC, 6Dasher, 243-Ackley's).
Donovan