Mainspring question follow-up for GT

4 Scale · 05-26-2015, 08:28 PM

Don the Luger mainspring G.T. was referring to was in a Luger he was working on for me, trying to improve the hold-open. Initially, hold open worked only 75% of the time on last round. He and I sent pistol parts, a complete pistol, and magazines back and forth for several weeks.

We were stuck for awhile; finally he tried a new MecGar that seemed to push the hold open up just a little higher. That, and a slightly weaker mainspring, resulted in perfect hold-open function.

The pistol was "weird". A '38 frame with a replacement Mauser-proofed barrel. The receiver had been marred externally by whoever replaced the barrel; we think they likely twisted or somehow altered the receiver geometry and that put some drag on the toggle action. I.e., at least part of the problem seemed to be, the breech bolt was not traveling far enough on recoil to engage the hold-open. We deduce that because cutting coils of the mainspring improved hold-open reliablity.

If G.T. hadn't thought to try that new MecGar, we'd still be messing with the mainspring. Or given up, it was a very long story and I'm leaving out a lot. I just wanted to let you know, the fix seemed to be the combination of slightly weaker mainspring and a new MecGar. One way to get a slightly weaker mainspring is to cut off 1/2 coil at a time and test. We also used tape on the back of the receiver to see if the toggle was striking the receiver - sometimes it was, sometimes it wasn't.

Per your specific question, we used 115 gr. WWB exclusively. I had heard that Lugers can be finicky about magazines, that not all magazines work correctly with all Lugers. Boy is that ever true.

Fortunately for me G.T. has the patience of a saint and (like me) enjoys the thrill of getting recalcitrant Lugers to function correctly. Without his help I doubt the pistol would run perfectly like it does now. Pending G.T.'s comments, that is my 2 cents.

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05-26-2015, 08:28 PM	#3
4 Scale User Join Date: Nov 2014 Posts: 544 Thanks: 194 Thanked 490 Times in 251 Posts	Don the Luger mainspring G.T. was referring to was in a Luger he was working on for me, trying to improve the hold-open. Initially, hold open worked only 75% of the time on last round. He and I sent pistol parts, a complete pistol, and magazines back and forth for several weeks. We were stuck for awhile; finally he tried a new MecGar that seemed to push the hold open up just a little higher. That, and a slightly weaker mainspring, resulted in perfect hold-open function. The pistol was "weird". A '38 frame with a replacement Mauser-proofed barrel. The receiver had been marred externally by whoever replaced the barrel; we think they likely twisted or somehow altered the receiver geometry and that put some drag on the toggle action. I.e., at least part of the problem seemed to be, the breech bolt was not traveling far enough on recoil to engage the hold-open. We deduce that because cutting coils of the mainspring improved hold-open reliablity. If G.T. hadn't thought to try that new MecGar, we'd still be messing with the mainspring. Or given up, it was a very long story and I'm leaving out a lot. I just wanted to let you know, the fix seemed to be the combination of slightly weaker mainspring and a new MecGar. One way to get a slightly weaker mainspring is to cut off 1/2 coil at a time and test. We also used tape on the back of the receiver to see if the toggle was striking the receiver - sometimes it was, sometimes it wasn't. Per your specific question, we used 115 gr. WWB exclusively. I had heard that Lugers can be finicky about magazines, that not all magazines work correctly with all Lugers. Boy is that ever true. Fortunately for me G.T. has the patience of a saint and (like me) enjoys the thrill of getting recalcitrant Lugers to function correctly. Without his help I doubt the pistol would run perfectly like it does now. Pending G.T.'s comments, that is my 2 cents.