Better to show a pic.


L to R
#1 New RP case
#2 Fired RP case (Ruger #3)
#3 Factory Remington cartridge
#4 Inert once fired ( fired in the Krag)
#5 Inert w/ new RP case

As you see both fired cases from two different rifles match the SAAMI spec for the 30-40. I have new Winchester cases and they measure the same as the Remingtons.

New Winchester cases are the same as the new Remington's

Difference from new case to fire formed cases.
Temp: 65 degrees

Chrony: Magneto Speed.
Rifle: Ruger #3 22" barrel

New 30-40 RP brass
CCI200 Primer
150 grain Sierra BT
COAL 3.08

Load 1- 2531fps
Load 2- 2598fps


Fired/FL Sized 30-40 RP brass
CCI200 Primer
150 grain Sierra BT
COAL 3.08

Load 1- 2686
Load 2- 2717



Why are the new 30-40 case not to SAAMI specs?

But the fired cases from the Ruger and Krag rifles are.

Brass that head spaces off of a rim is often short at the shoulder to fit, fire and function in a multitude of guns.

New belted mag and other rimmed cases suffer the same "fit all" symptom.
Rimless cases can also exhibit enough variance except they misfire

Yep. My .30-30 moves the shoulder forward .026" when first fired. I just bump it back .002" when I size.

Paulh-
Actually, I cannot see whether any of these cases match SAAMI specs. My eyeball isn't sufficiently calibrated to find, for example, whether your case body diameters fall within the SAAMI spec of 0.4142" min to 0.4222" max at a distance of 1.600" from the case head.

What technique did you use to measure the dimensions of the fired and unfired cases?

Are you perhaps assuming that a case fire-formed in your rifle's chamber will conform to SAAMI specs? At least in the case of your Krag rifle (if it still has the original chamber from Springfield Armory) that may not be true. SAAMI standards were not established until about 30 years after they stopped making Krag rifles.

What do your fired cases look like after they have been full-length resized? Do they still conform to SAAMI specs?

Just curious.

--Bob

Fired and FL resized cases are SAAMI. I used a caliper to measure. The new RP and WW cases are not as in the pic.

The shoulder difference doesn't make a difference in the krag, but the Ruger is loaded heavier. Therefore I will fire form them before working up loads in the ruger.

FWIW I've found much the same thing with rimmed cases from .22 Hornet to 9.3x74R: they all start out a bit smaller than the chamber, and fireform to fit after the first time they're used. Perhaps the most extreme examples are my .303s, especially the wartime-production No. 4 I have.

I have never worried about it. I work up loads in fireformed cases and neck-size only, to save excessive working of the brass. I'd suggest keeping the brass for each rifle of the same calibre separate though, which is what I do.

Does this mean misfires are more likely with rimmed cartridges?

Steve.

No.