Determining Chamber Pressure


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RoGrrr
August 28, 2011, 03:15 PM
I recently bought a Rock Island 9mm 1911 for concealed carry. I shot about 1000 rounds of factory ammo in it to break it in and decided it should be ready as my carry weapon.
I loaded the mag with +P+ and racked the slide. It jammed. I cleared it and re-racked it. Another jam. After 6 jams I realized it would not feed this shortened hollow point ammo.
As I researched more, I learned that 9mm 1911s do not like the shorter length of hollow point ammo. I know that if a bullet is seated deeper in the case, the chamber pressure goes up, in some cases, astronomically. The normal chamber pressure for 9mm is in the 30,000 PSI range, while +P+ is around 38,000.
I surmise that if I reseat the hollow point slug to whatever the recommended max length so it feeds (I donít have my manual handy and disremember that spec), the chamber pressure should drop and I will not have my desired +P+ characteristics.
Since SAAMI does not even mention +P or +P+ ammo, I have no way to determine what loads I should work on to develop a longer overall hollow point +P+ load.
So at this point Iím wondering about building a pressure tester. I have the machining facilities to build such a test setup and wonder if anyone has built a transducer-type tester so I can directly read pressure on some type of digital readout.
DISCLAIMER
This is not something I would be doing for anyone else so donít bother telling me about any liabilities. Thatís all crap and all lawyers should be killed, as they have abused their once noble craft to the point of everybody suing everybody else for everything. Now go awayÖ.

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243winxb
August 28, 2011, 04:26 PM
wonder if anyone has built a transducer-type tester Oehler may be? http://www.oehler-research.com/ism83.html SAAMI 9mm Luger +P is rated at 38,500 PSI. Proof loads at 55,500 PSI. http://www.saami.org/specifications_and_information/publications/download/205.pdf

rfwobbly
August 28, 2011, 10:42 PM
You issue has nothing to do with chamber pressure, and everything to do with the shape of the bullet's nose, the shape of the feed ramp, and the magazine lips. The 1911 was designed to shoot a much longer round than 9x19, that's why all the other 1911 are offered in longer cartridges such as 9x21, 9x23, 38 Super, 10MM, 45ACP, etc.

Highly suggest you start with a Rock Island forum, if there is such a thing. That or else you'll need to sit down with 10 or so different manufacturer's ammo and try them all to find one that feeds reliably for SD.

Or you could always have your gun converted to 38 Super and use the 9mm for target practice.

Jim Watson
August 28, 2011, 11:38 PM
Or try some different magazines.
I don't know what RIA supplies but I would look at Tripp Cobramag, Wilson ETM, and Metalform/Springfield Front Ramp.

Unfortunately I can no longer find the specific Metalform .38 Super magazine, their no 38-297, that works so well in my and friends' 9mms. They have gone to special order status at Metalform and since they only hold 9 rounds, apparently nobody cares enough to order a production run of them.

I don't know about industrial type piezoelectric transducers, but there is reasonably affordable - more than your RIA, less than a Kimber - strain gauge pressure gear. Won't work in an auto (neither would a piezo) so you will have to get or build a testbed. A Contender is the usual DIY because of the readily interchangeable barrels. So if you just must...
http://www.shootingsoftware.com/pressure.htm

56hawk
August 28, 2011, 11:52 PM
I had the same problem with a 1911 in 40 S&W. Jammed all the time until I loaded the bullets out to 1.200 which is about 10mm spec. It works flawless at that length.

As far as loading to +p+ goes I'd just start with a max load 9mm and work up until you start to see pressure signs. You might need to switch to a heavier recoil spring at some point though. You also might want to find some USPSA shooters who load 9mm major. They should have some good load data.

Another thing to think about with a 9mm 1911 is that it was designed for 45 ACP. You have a lot more metal around the chamber in 9mm and can bump the pressure way up. Back when I was shooting competitions with a 38 Super I was loading a 115 gr bullet to 1600 fps. No idea what the pressure was, but my reloading manual lists 30,000 psi to get 1300 fps.

gamestalker
August 29, 2011, 09:51 AM
Your not going to loose enough to be noticable by increasing the OAL to a functional length. If you have a chronograph run a few through at the original length and then some at the functional length. If it slowed down more than you can live with just start working the load back up until it suffices.
Your powder choice is more of a determing factor regarding velocity than is OAL. Use a real slow burning powder and seat the bullets to the functioning OAL and enjoy a +P+ performance, nothing to it.

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