Recently I got a new heavy Lothar Walther custom barrel (German make)on my Remington 700 Sendero, .270 Winchester. Seemed a good idea to start my load development with new brass, RWS. Measuring the new brass in the precision mic of RCBS, I found -0.002". So far, so good. I fired some 6 rounds, just to get started and to zero my Swarovski scope. Measured again in the mic: minus 0.005"! Hodgdon 4831sc, CCI br primers, TSX 130 grains, gap 0.050 inch. No signs of high pressure. How come?
Thanks,
Jan.

I would imagine that as the case stretches to fill the chamber it pulls the brass back a bit...the opposite of it growing when you full length size.

Jan,

I wouldn't say this a common occurance but it's not unheard of either but this normally occurs when some sort of case manipulation, wildcat or re-forming has occured.

I have just had exactly the same occurance with the same cartridge, a .270 Winchester in a Ruger #1B rifle.

I think it's dependant on the chamber, the cases and (without insulting you) the person's ability to use calipers that are/were zero'd properly.

I would imagine the cases have expanded to fit the rifle's chamber.

When you reload these cases I would start by ensuring that the Dies are adjusted properly with the once fired cases and intermittently checking as you adjust the Dies to see if the cases fit correctly in the chamber. A tea candle to soot the case neck will depict very accurately where you are on the neck and if setting the should back when re-sizing.

Let us know how you get along?

Jan,

If you are measuring fired unsized cases , don't worry they will get longer after sizing.

Exactly the reason to trim after ( not before ) sizing the case .


Travis F.

The first firing often shortens cases, particularly if the case shoulder has to expand significantly to fill the chamber.

.22 Hornet cases are visibly shorter after their first firing in my K-Hornet chamber. In fact, they're shortened so much by the fireforming that they never grow enough, even after many firings, to require trimming.

I would infer that your .270 has a rather generous chamber, which results in a shortened case on first firing. As noted by others, full length sizing will likely cause the case to re-lengthen measurably.

Thank you folks, for your input. I think the chamber could indeed be a bit generous, but the barrel performs very good, up till now. I adjusted the FLR die just slightly, so the cases keep about the same length now as after fireforming.
And Gerry, don't worry about my caliperhandling, I reload for some 20 years!
Nice day,
Jan.