why do Super cases grow?

[ErikW]

Invariably, if my once- and twice-fired RP .38 Super +P brass cased loads fail in the Dillon gauge, it's because the case stretched beyond maximum length. What's up with that? The reject rate is somewhere under 0.5%.

They started as new brass, loaded with 3N37 or N350 and a 115 JHP. Fired only in my Nowlin-barreled Open gun.

[dillon]

What do the cases individually measure before and after sizing? Measure a case before sizing, then again after sizing.Typically, straightwall cases get shorter after firing, due to molecular compaction, but only after extended use. Please post the results here, or call me at Dillon-1-800-223-4570 ext 311

[ErikW]

Measure new brass? Can't; loaded and shot 'em all.

Measure fired before resizing? I'll check. I've only measured the failed ones... something like .897" IIRC.

[dillon]

Eric,

SAAMI specs call for a maximum case length of .900", with tolerances of +.000", -.010". I suspect perhaps another cause for your chambering problems. Maybe have a gunsmith check the chamber dimensions.

[bompa]

I remember years ago when I was shooting a lot of heavy loads in 357Mag that the brass had to be trimmed quite often..Perhaps it only happens with hot and heavy loads...

[BSeevers]

My 38Super brass shrinks.

[10ring]

I've recently started loading 38 Super so I can share my experiences.  My first brand of brass I've tried is Remington 38 Super +P.  I checked the new case length and trimmed when necessary so they were all 0.894" to 0.897".  I loaded some up to work up a load and have gone back to measure the case lengths of those initial fired rounds.  The few I measured were 0.885" to 0.893".  Therefore from my initial experience it appears as though new cases tend to shrink; probably due to the brass filling out to full dimension?

I also noticed that the max case length spec is at 0.900".  You may be dealing with a short chamber.

Hope this helps.

[Patrick Sweeney]

Brass usually shrinks on the  first firing, as the cylinder expands to fill the chamber.  Sizing lengthens it again, but not enough to get back to the original.

Rifle brass expands again and again due to the extreme pressure, and the neck expander pulling through.  Handguns don't experience the same stresses, so rarely need trimming.

Measure the depth of your case gauge.  Measure the depth of your chamber.  Max is supposed to be .900", and it is a tight chamber that goes less than .905"  And long brass that goes past .895"  You might just be the one guy in America with a short chamber and long brass, and experiencing the problem.