Seating Depth And Case Expansion Change During Production

[6Gears1Speed]

I don't know what happened to give me that 1 at 1.140" It is pretty rare for me to have one this far off.

My wild guess is that for that one round for whatever reason you didn't pull the arm all the way down/ram all the way up so it seated a bit long. Did someone or something interrupt you while you were running this test?

[Steve]

I don't know what happened to give me that 1 at 1.140" It is pretty rare for me to have one this far off.

My wild guess is that for that one round for whatever reason you didn't pull the arm all the way down/ram all the way up so it seated a bit long. Did someone or something interrupt you while you were running this test?

Negative on the interruption. I should have checked the bullet when I found the cartridge was long. My seating plug fits the ogave/taper of the bullet. What I have found in the past was bullets that were maybe cold when cast so they didn't fill out the seating plug which lets the tip extend further. Usually my cartridges stay within 3 thousandths.

[Fyodor]

Do you measure on the same spot that your seating plug touches?

If you seat on the taper, but measure on the top, a slightly different bullet form might end up in a "large" deviation in seating depth. Depending on the angle of the taper, it acts as a kind of "gear" with an transmission ratio equal to the cone ratio. In an extreme case even casting temperature could have an influence there, because the shrinkage is different.

Try making an adaptor ring for your caliper, so you measure the same spot that you seat. Otherwise you don't measure what your press and fires are doing only, but also some other influences that you don't know.

[Steve]

Do you measure on the same spot that your seating plug touches?

If you seat on the taper, but measure on the top, a slightly different bullet form might end up in a "large" deviation in seating depth. Depending on the angle of the taper, it acts as a kind of "gear" with an transmission ratio equal to the cone ratio. In an extreme case even casting temperature could have an influence there, because the shrinkage is different.

Try making an adaptor ring for your caliper, so you measure the same spot that you seat. Otherwise you don't measure what your press and fires are doing only, but also some other influences that you don't know.

You are 100% correct Fyodor. When I measure using the method you describe the length when using once fired good condition cases the measurement stays within 1 thousandth.

But if my OAL exceeds 1.140 by not much I have feed problems in my M&P. So I think the variance in OAL I do have with these cast bullets basically says the bullet quality is vary high. I load 223 Remington on the Loadmaster using a 3 point contact with dies. With good quality bullets, and good matched cases the 223 does not vary when measured on the ogave of the bullet.