The strangest of things with Sako brass

[Sim G]

In the depths of the shed I found a box of .44 mag brass, just over a couple of thousand from the pistol days. Getting low on loaded stuff so had the tumbler going for a couple of days and have just finished loading a thousand.

There was all sorts on there. Mixing brass in pistol calbers has never bothered me and I have never found a difference at the ranges I shoot the .44, but we had Howitzer, Winchester, Norma, Remington and even some H&F! And some Sako.

Anyhow, I'm loading it on my Dillon as I have done for 27 years. And, using the same Lee dies that have loaded for two revolvers and three rifles chambered in .44. Now here's the thing, the Sako brass would go through a full length resize, and then "spring back" to it's unsized size!!

Everyone of them would let a .429 bullet slide into the mouth and hit the bottom of the case with ease. Run them through the FL die and the bullet again would just slide in. No matter how many times it was run through the die. There were no problems with any other cases, just the Sako. I sifted what I thought was all of them but still missed a couple, well eight actually, and when running a progressive I only found this out after it had "cost" me a primer.

Any ideas why this would happen?

[dromia]

Need annealing?

Brass thickness/thinness?

Faeries?

[ovenpaa]

I would say the brass was thinner.

I had this with some .308 Federal once fired I picked up once, I cleaned it, put it through a full length size, trimmed it to length and chamfered the neck and uniformed the primer pockets on 100 cases before priming 100 of them only to find the bullets could be seated with finger pressure.

[Chapuis]

Picked up from another website is the suggestion that the cases need annealing because they have become work hardened or weren't sufficiently annealed in the first place. The result is that they spring back to the unsized dimensions immediately on removal from the sizing die rather than remaining at the the resized dimensions.