Case Length Growth Question

[Bill2905]

Since I adjusted my FL bushing die to bump shoulders about 0.002, my Lapua 6BR cases show very little growth in length, if any. However, when I resize a batch of 40 cases, there will always be 2-3 that increase about 0.005 in length as compared to no increase for the remainder. I should note that the expander ball was still in the die when I made these observations. What could be different about these cases to cause this? They were all fired with the same load in the same chamber.

[Robinhood]

Minimal information means everything is generalized or a shot in the dark for answers. How many firings? Do you anneal? What is your load?

Brass flow is usually minimal with a 30* shoulder. Softer brass will flow more, so if some have been fired more than others I would expect it.

[Bill2905]

Minimal information means everything is generalized or a shot in the dark for answers. How many firings? Do you anneal? What is your load?

Brass flow is usually minimal with a 30* shoulder. Softer brass will flow more, so if some have been fired more than others I would expect it.

2 firings

No annealing

70 gr SMK HPBT with 27.0 gr H322 and Berger 68 gr HP with 30.0 gr W748 are the two loads I have been shooting. The cases are all from same mfg lot but I don't separate them by load type after firing.

I use a Redding type S FL bushing die.

I don't view this as a problem. It's just something that aroused my curiosity.

[Bill2905]

My original statement that they all fired the same load was incorrect.

[Robinhood]

i wonder if they came that way from the factory???

[Fuj']

It could be what Robinhood mentioned about annealing and softer
brass. The factory brass is annealed, but that does not mean each
case is the same. I just finished another 50 Norma cases for my
wild cat. Cases are from the same lot. I had at least 7 out of the
50 that sized on the easy side and 4 harder then others. The hard
cases will generally show a bit longer then the softer ones. Typical
spring back.

[charlie b]

I have always had some cases that needed trimming while others do not.

My latest brass was Lapua .308. All were ok when I received them. After 5 loads none needed trimming. At 10 loads some did. By 15 all of them had been trimmed at least once and some twice.

Keep in mind that these cases will see cast loads at reduced velocity and jacketed loads a full velocity. The cast loads are set so the bullets are jammed into the lands while the jacketed loads have a jump (usually .020"). As far as I understand the physics in the chamber that alone will cause different case stress.

[Bill2905]

I do notice that a few cases will require more press force to complete the sizing and some seem easier. I never looked at those cases but next time it happens, I will take a closer look and measure them.