Measuring Case Bulge

[EdMc]

I've read of this while lurking at this site and many others as an indication of pressure. Loaded some rds, 185 XTP with LS at 0.3 of powder intervals of 8.3 to 9.2 gr. All powder measurements were individually weighed etc. Starline brass, Coal 1.600 with WLP primers. Crimp was set at 0.423. Velocity hit 1200 with one rd at 8.9 grains but all loaded at 9.2 grs fell below 1200 fps. Stock spring and barrel Golck 20 SF. Bulge readings varied at all levels with some higher than others. Largest at 9.2 grain was .4335. (Starrett .0001 mike) Crimps measured with a Starrett dial caliper.

I reloaded some more at 9.0 gr LS with a crimp of .421. No chrono used as these were fired at an indoor range. Largest bulge was 0.4348 with some subtle primer changes like I'd seen with the first group at 9.2 grains.

My only reference for measuring was some Atlanta Arms range rounds that had been loaded in Starline cases with 185 gr FMJ bullets of unknown source. These measured under 0.4330 by random samples. At the time I didn't remember to save a rd to measure the crimp nor COAL.

Also had two old stock boxes of Federal Classic ammo.......these were of two types, one with brass colored primers with a crimp of 0.421 and COAL ~1.400. The others had silver colored primers with a crimp of 0.419 and COAL ~1.500. Both were FMJ with flat points like the AAR. These also were not fired over a chrono had measured bulges of ~0.433

As for my stupid question what do I take from all this? My desire is to load some accurate rds with Starline, LS and 185 XTP at over 1200 fps. I will try to chrono the Fed rds and also the 9.0gr reloads at some point shortly. I'm thinking the added crimp probably added to the pressure of the 9.0 gr reloads judging by the extra case expansion.

[The_Shadow]

The COAL's have my concerns, as the 10mm is usually at 1.250" give or take!
Loads from my Glock 29 factory barrel do get to 0.4340"-0.4345" with 9.4 grs of LS under the Hornady 200XTP's at 1177 fps where as those same loads at 0.4295" from my S&W 1006.

I don't pay too much attention to the crimp as many cases vary in thickness, but I test to insure no bullet movement with a slight shine on the edge of the case mouth showing the taper crimp is working the area.

[DM1906]

When you say "measure the case bulge", are you referring to the case head/wed, or the actual bulged area of the case?  The case can only expand to the chamber dimension, where it is supported.  This is why we measure the case, OUTSIDE the support (Water's Method).  A Glock OEM barrel chamber is quite generous, and can exceed that of better supported chambers.  Smiles, on the other hand, are a completely different condition.  This is expansion outside the chamber.  Measure the case rim, and web just forward of the rim (behind the chamber support area) for the best representation of actual case head expansion.

[EdMc]

I used the 1.26 length from Hodgdon's reloading site as they show a higher max level for loading LS than any manuals I own. I also don't know the bullet length difference of the XTP and the bullet used in Hodgdons's testing. Seemed safer to to give more case room.

I measured the cases by turning and moving them sightly up or down just above the extractor groove until I found the max measurement. Hope I'm not proving John Wayne's axiom.

Thanks

[DM1906]

I used the 1.26 length from Hodgdon's reloading site as they show a higher max level for loading LS than any manuals I own. I also don't know the bullet length difference of the XTP and the bullet used in Hodgdons's testing. Seemed safer to to give more case room.

I measured the cases by turning and moving them sightly up or down just above the extractor groove until I found the max measurement. Hope I'm not proving John Wayne's axiom.

Thanks

Just asking the question, and the reason for asking.  Not busting your chops, or anything.

How you describe the measurement sounds OK, but I've found it to be more consistent if measured at the same location along the case, every time.  I use a caliper (digital or analog, both calibrated), measure the rim (careful to not get an extractor/ejector nick), and the web with the caliper edge at the rim forward edge.  Moving forward of that gets into the chamber support, with isn't offering an accurate measurement of expansion (caused by excessive pressure).  If the rounds were fired in an OEM barrel, I measure the bulge area, just as a reference of chamber fill (it will almost always be less, unless the round is at or near maximum pressure for that barrel).  What is more important than the actual measurements, is the trend that develops.  Once you have an established baseline measurement, the pressure trends are easy to track, and pressure limits are easier to identify.

[sqlbullet]

Ed, in your original post I think you left a "2" out of your COL measurements.  That was the source of Shadow's concern.  1.260" and 1.240" are numbers we are familiar with.  1.600" and 1.400" are not, at least with the 10mm.

As I am sure you have read, a bulged case is a dead case for safety reasons and a definite sign that max is exceeded for that gun regardless of charge, pressure or reloading manual specs.

DM1906 has given you good information about measuring the case head.  If in doubt section one for reference about where the chamber supported brass ends and the actual case head begins.  You want to measure the head.  This part of the brass will flow under high pressure.  And, again, you are looking for trends.  So, as you work your loads up, if you start to see unexpected increase in the measurement, time for concern.

I know this all seems a little vague.  The truth is you can't really know unless you have a pressure barrel.  These other items are indicators.  For guys that have been reloading a while we have seen several methods be deemed "good indicators" later to be debunked.  Right now case head expansion is trusted by many of us, probably because it mimics in a non-scientific way the old copper crusher method.  We are measuring how much a brass pill is deformed.

Hope this helps.

[EdMc]

Oops.....knew I shouldn't have posted after being sedated this am.  (two level nerve block on my back) I did leave out an important '2'. 

I think I get the correct way, measure from the upper edge of the rim up with the caliper......No problem with the question, my comment on the sig was meant as humor. Mine doesn't come across well on the internet....sometimes. I'll go back and remeasure all again.

Thanks.