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Posted: 11/27/2008 7:04:02 AM EDT
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I just go a new 22lr upper with a 7.5 inch barrel. I put it on a new lower with a standard lower parts kit. I've only fired Blazer through it.
The lower function tests are fine and the disconnect is working like it should. BUT Every once in a while it fires two bullets instead of one. (I'm very concerned, I don't want an illegal weapon.) Did anyone ever encounter this before? What are the solutions to fix this? Should I send the upper back? The only thing I can think of is that the disconnecter spring is too strong and there isn't enough blow back from the bullet to force it all the way back. |
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Your hammer spring is too strong - the bolt is not getting quite enough momentum to push the hammer back to engage the disconnector, so the hammer is following the bolt forwards. You have two options:
1) Use more powerful ammo... CCI MiniMags would be a good starting point. 2) Replace the GI hammer spring with a reduced power spring, such as the JP yellow spring. I had the exact same problem with my 7.5" upper and Ciener kit, and the yellow spring 100% cured the problem. It also improves the trigger pull, which is a nice side benefit. ETA: gratuitous photo: 
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It's a Model 1 Sales upper.
I have the disconnector spring installed. I took a few coils off it and it seems better. I'm also going to try a JP yellow spring. I don't think I'll have light strikes on the rimfire so I'm not worried about them loosing tension. But you never know. |
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Quoted:
Your hammer spring is too strong - the bolt is not getting quite enough momentum to push the hammer back to engage the disconnector, so the hammer is following the bolt forwards. You have two options: 1) Use more powerful ammo... CCI MiniMags would be a good starting point. 2) Replace the GI hammer spring with a reduced power spring, such as the JP yellow spring. I had the exact same problem with my 7.5" upper and Ciener kit, and the yellow spring 100% cured the problem. It also improves the trigger pull, which is a nice side benefit. ETA: gratuitous photo: http://i244.photobucket.com/albums/gg34/stealthyblagga/SBRAR1522RF.jpg 100% Correct. |
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Quoted:
It's a Model 1 Sales upper. I have the disconnector spring installed. I took a few coils off it and it seems better. I'm also going to try a JP yellow spring. I don't think I'll have light strikes on the rimfire so I'm not worried about them loosing tension. But you never know. I thought the Model 1 Sales upper came with a reduced power hammer spring... no ? |
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Quoted:
Quoted:
Do the lighter springs cause any problems when switching back to a .223/5.56 upper? Not in my case... I have two rifles running the yellow JP hammer spring, and I cannot ever recall having a light strike. In my experience the lighter spring will run the 5.56 fine but may cause light strikes in the rimfire unit . I believe the centerfire fireing pin requires less of a wack to run 100% |
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Here's an update:
I just got the yellow springs in. They stopped the double firing but as nhsport has said above ^^ they produced some light strikes. I had a few fail-to-fire. Not sure if there is a happy medium. I'm going to try some of the other recommended ammo above. See what that does. |
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