Interarms 9mm luger now fully reliable

[Sieger]

Originally Posted by nok

I have a circa 1975 Interarms Mauser 9mm luger, 4" barrel. It was basically unfired when I obtained it. Pretty, yes. Reliable, no way. I don't think it would make it through an entire magazine for the first few years I owned it. I didn't get to shoot all that much, but recently an indoor range opened (to the public). This gave me a much needed opportunity to chase down some variables. I can tell you this: At the range tonight, out of 100 rounds fired, I had one jam. Last time out, zero jams.
I'm only posting this in case anyone else with the same gun is as frustrated as I was. Firstly, most of the conventional wisdom turned up in my research was exactly wrong. This particular firearm DOES NOT like "hot loads". It also likes shorter COAL. I had bought some UMC 9mm FMJ at a gun show, and it performed better than anything else I had ever used. These cartridges are visibly shorter than any other commercial ammo I checked. I now load all my Luger rounds at 1.121". Secondly, I changed magazine springs. I still think a more powerful spring would help, but all I could find were Wolff springs @+10%. I'm thinking of winding some springs of my own since I can easily hand-load a Wolff-equipped mag even without the loading tool (others say they just cannot get that eighth round into the mag). Thirdly, I changed extractors. Repros are available from Numrich, along with much stronger extractor springs. By the time I had made these changes, I think the gun was about 75% reliable. Better, but still frustrating.
The final piece of the puzzle was changing to a different powder. I had some success after doing trials with Unique, but nothing I would consider definitive. It seemed from my reading that original luger rounds were loaded with a slow-ish powder. The answer to that turned out to be Winchester AutoComp. After fine-tuning the charge, I have finally been able to fully enjoy this Luger. I love the gun and succeeding in making it reliable has made it my favorite at the range.
My reloading recipe for this pistol is:
Remington FMJ 115 gr. bullets
Winchester Small Pistol primers (although I would try CCI500's)
5.4 gns. of AutoComp powder (gives about 1100FPS)
Cartridge over all length=1.121"

Hope this helps somebody or gives them a couple ideas if they're having trouble with their own Luger, whatever the vintage and make.

Hi,

I'm happy you are enjoying your Luger and that it is now functioning properly for you!!!

Some of the problems you experienced with your Interarms Parabellum are a bit puzzling to me, but, on the other hand, I'm not one to argue with success.

Original recoil springs on these were quite strong from the factory; as were the magazine springs, that were timed to the recoil springs. If, as you say, you can easily pull your magazine spring down for the eighth round, with your bare thumb, there is something very, very wrong with your magazine spring.

Your C.O.A.L. figures are totally puzzling to me; as your round nose bullets, if you are loading and shooting from a fully loaded 8 round magazine, should jam like the Devil at that short of length. The well established C.O.A.L. for round nose bullets is 1.173 inches and has been since the introduction of the Luger, per original German DWM and Mauser sources. Also, for future bullet types, you may wish to read my sticky "Determining Proper Cartridge O.A.L", as it may be helpful.

I fully agree that Lugers prefer slower powders, as my most accurate and reliable powders are in the exact same burning range as your Winchester Auto Comp powder.

Lugers do not prefer "Hot Loads" as you can now also attest.

I've also experience week extractor spring problems; which, by the way, is one of the major causes of "smoke stacks" in a Luger.

Again, good luck shooting your very fine Interarms Parabellum!!!


Sieger