brass case expansion after firing

[jim v]

Has anyone measured their brass diameter after firing and compared it to their chamber dimension?

I get a difference of 1.5 to 2 thou larger on my fired brass.

The primary difference is just above the solid case head - i.e. about 7mm above the extractor groove.

The simplest description is that a fired case, when clean, will not enter the barrel chamber.

This expansion is the same for new or very used brass.

Whilst my setup is close to 100% reliable, I am worried that I may have missed something.

The details are 9x23 Starline brass, 123 grain Lee FP cast bullets, 8.9 gr S221 powder, OAL 31.5mm, F165-168,

15lb mainspring, 8lb recoil spring, normal firing pin retaining plate, 300 gram slide, STI Trubor barrel/comp.

The ejection pattern is consistent at 2m. No elongation of the firing pin indentation is apparent.

[dover0020]

All brass expands when it is fired. The sizing die will get it back into spec when you reload it.

[jim v]

Why should the brass case expand to more than the size of the chamber?

[yoshidaex]

Why should the brass case expand to more than the size of the chamber?

STI barrels have good case support.

Is it possible the feed ramp angle was smoothed over/modified to help with feeding?

Edited September 3, 2012 by yoshidaex

[Action Pistolero]

Pretty much all I shoot these days is 9x23 with Starline brass. My fired brass falls right in the chamber. Will the case go into the chamber at all?

It would seem to me that with your spring set up and the power factor, you may have a timing issue. In other words, the slide is unlocking before the bullet is leaving the barrel. The case is still expanding as it is being ripped out of the chamber. The reason that the bulge starts 7mm up the case is because the web of the 9x23 case is very thick.

I would suggest upping the mainspring to a 17 and a at least a 9lb recoil spring.

[Miranda]

ooof.

ok how did you measure them?

a dial caliper?

inside diameters with calipers are usually off by about 3 thousands

also,I rarely get consistant id readings.

try fitting the case into the chamber that fired it...

miranda

[Hi-Power Jack]

try fitting the case into the chamber that fired it...

Miranda, Jim said that the fired brass (cleaned) will NOT

fit back into the chamber ???

[jim v]

Thanks for the replies.

I will tackle this problem in 3 phases:

1 ensure that the barrel lockup is sufficient (the current primer strike is a little bit off center)

2 increase the weight of the mainspring

3 increase the weight of the recoil spring

I will give feedback on these actions later as I do not want to change anything before the level 4 in Bulawayo next week.

Many thanks to all

Edited September 4, 2012 by jim v