Little Crow Gunworks: Avg POI Is More Important Than Group Size. Thoughts?

[Niles Coyote]

A little more food for you all

 

[flogxal]

Region Rat -- great post, thanks. The stick-slip situation I have felt. Too much case lube in the wrong place (shoulder), done that too, seen the depressions/craters on the shoulder. Collapsed a few shoulders. I am learning the hard way for sure.

It seems the problem easily created is the pull on the case mouth from the button drawing back up. Too much friction there. And pulls the shoulder away from the case head side of things.

In the past I did a little CrMo steel tube work and the cold forming of curves in tubes -- different from brass sizing in a few ways, I know -- that's done slowly against a form, in order to not cause folding/accordion ripples on the interior bend of the curve. Maybe my brain sits there and makes me go too slow.

 

[straightshooter1]

Many folks tend to size too slowly, and that opens the door for a different kind of friction problem.

If you have ever seen the speed of the machines in a factory, they are not moving slow. By that same token, they are not going as hard as LCGW either.

What it takes is a pretty good velocity into the stop without slowing down and getting into what is called a "stick-slip" friction problem. The really hard slam into the stop isn't really required, but if that is what it takes to avoid the friction regime change for you, then slam away.

You can practice with cheap brass and check your headspace. The problem shows up as variation in that shoulder datum length. It is better to go a little faster than it is to go a little slower and accidentally get into stick-slip.

Make sure you don't get sloppy with case lube, or you also introduce problems. More is not always better, and too skinny can also be bad.

Brass is magical in terms of how well it is suited to cartridge use. It has a shear storage, and shear loss term built into the modulus, as well as a damping term. When you cold work it, you want to be as consistent as possible with your speed while avoiding that stick-slip which is like dozens of starts and stops. YMMV

This is one of the things I noticed and, as I so often to, ran an experiment of some range brass I picked up. I changed speeds in how fast I rammed my cases into the sizing die and measure to results. The results changed with the speed, like faster resulted in more springback and less consistency. And with my bushing sizing dies, which I just don't use anymore, there was a big difference in concentricity (faster was better). My lubing procedure works well with decent speed getting case into the die and giving my annealed cases a few seconds dwell time in my non-bushing FL sizing die has given me my best results. I guess a good lubing help with that.