latech15 Posted April 12, 2011 Share Posted April 12, 2011 I have a 9mm SVI open gun. I bought it used so I am not sure of all of the specs, but here is the issue: When I rack the slide and dry fire, everything is cool. When I thumb cock the gun, the hammer travels a bit farther than when it is cocked by racking the slide. If it goes this little extra distance, pulling the trigger won't drop the hammer. I can usually tap the grip safety and get it to pop back up and set correctly so that it will drop the hammer upon pulling the trigger. It is being cocked to a point where the sear is past the hooks on the hammer. My first thought was to go with a new mainspring. I ordered a ISMI 17 lb spring and replaced the old one with it. It is about 1/4" longer than the old spring, and it is noticeably lighter. The problem is worse with this new spring. Should I order a higher power mainspring, or is there something else that I am missing? My limited gun's hammer has this little bit of extra travel, but the tension is much stronger and it just bounces back up if I thumb cock it all the way down. Link to comment Share on other sites More sharing options...
ParaGunner Posted April 13, 2011 Share Posted April 13, 2011 Check for burrs below the hammer hooks and check your main spring cap,make sure the mainspring cap is round and doesn't have any burrs. Also,maybe the hammer strut is out of spec. Link to comment Share on other sites More sharing options...
want2race Posted April 13, 2011 Share Posted April 13, 2011 Any 1911 can replicate this if you take the grip safety off and thumb the hammer back. It over rotates and will stay down. Your issue is that it does it with the grip safety on. The first thing to check if it stays back during LIVE fire. If it functions 100% at the range, don't bother changing it. When you thumb the hammer back to dry fire, just push it back up so the hook is resting on the sear again. Link to comment Share on other sites More sharing options...
latech15 Posted April 13, 2011 Author Share Posted April 13, 2011 Yes, live fire is OK. This whole issue came up last weekend when I was having issues with light strikes. I ordered an extended firing pin and new 17lb mainspring hoping to fix that problem. The extended firing pin fixed that issue but when I replaced the spring this one came up. I just want the thing to run reliably. Going to a heavier mainspring would make this more reliable, but I would get a little more muzzle flip in recoil, wouldn't I? Link to comment Share on other sites More sharing options...
yoshidaex Posted April 13, 2011 Share Posted April 13, 2011 Concur with what want2race posted. Also, hammer design may cause your issue also. Especially the spurless designed hammers. Link to comment Share on other sites More sharing options...
want2race Posted April 13, 2011 Share Posted April 13, 2011 Make sure to check that your firing pin does not protrude at all into the breach face. Some earlier ext. pins would poke out just a bit. I can run a 17#, but I prefer to install 19's to ensure ignition. The difference in recoil feel will be up to you. I don't think you'll notice the 2lb difference. You can also tinker with the profile of the firing pin stop to change the feel too. Link to comment Share on other sites More sharing options...
Tyshoots Posted April 14, 2011 Share Posted April 14, 2011 Make sure that the hammer srut is not contacting the grip safety. There is a slot that the strut rides in and sometimes it can rub on it. It can cause light primer hits. If the cap for your main spring has a grove wore in it when you cock it it might be sticking. When you activate the grip safety it is hit the hammer strut and will let the hammer fall. Link to comment Share on other sites More sharing options...
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