Pure speculation: if the barrel is too far to the rear, the bolt will not close perfectly, the gun should not fire. A buildt-in safety feature.
If the headspace is at mimimum, and some force is applied to chamber the chartridge, this may explain why the gun sometimes will fire, sometimes not. Just my 5 cents...
MG5 help needed
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I appreciate everyone's feedback and suggestions. Thank you to Jack and ghostrip (panagiotis) for the pictures. I have two separate issues and I think I'm on the verge of solving them.
The failure to fire (i.e., non-release of firing pin) I'm going to blame on a too-weak spring. When the sear is tripped it releases a lever (pushed by a little spring pushing a ball bearing) which hits another lever on the bolt which releases the firing pin. With the grip removed I can watch the little lever repeatedly hitting the firing pin release lever, apparently without enough force to actually disengage it. Sometimes 2 hits, sometimes 3, sometimes 5. Eventually it will trip the lever, just not on the first go. I'm going to try to find a slightly stronger spring which hopefully will give enough power so that the lever hits the firing-pin-release lever with enough force to trip it.
For the life of me, I can't find any explanation for why there was an apparent relationship between a difficult-to-chamber round and the lack of firing pin release. The two were related frequently enough to cause me to think there was some causal relation, but based on the design I can't imagine how.
The case bulges and ruptures I'll take the blame for and ascribe to a too-loose headspace (although I still think the groove in the barrel is way too deep), which would also explain the light hits. As the barrel pushes forward (increasing headspace) the extractor (under spring pressure pushing it against the chamber groove) goes with it, pivoting lower and lower below the edge of the chamber. The back of the extractor is curved, and the extractor slot is actually the end of a long groove cut in the bottom of the barrel, so it simply slips down as the barrel moves away from it.
The failure to fire (i.e., non-release of firing pin) I'm going to blame on a too-weak spring. When the sear is tripped it releases a lever (pushed by a little spring pushing a ball bearing) which hits another lever on the bolt which releases the firing pin. With the grip removed I can watch the little lever repeatedly hitting the firing pin release lever, apparently without enough force to actually disengage it. Sometimes 2 hits, sometimes 3, sometimes 5. Eventually it will trip the lever, just not on the first go. I'm going to try to find a slightly stronger spring which hopefully will give enough power so that the lever hits the firing-pin-release lever with enough force to trip it.
For the life of me, I can't find any explanation for why there was an apparent relationship between a difficult-to-chamber round and the lack of firing pin release. The two were related frequently enough to cause me to think there was some causal relation, but based on the design I can't imagine how.
The case bulges and ruptures I'll take the blame for and ascribe to a too-loose headspace (although I still think the groove in the barrel is way too deep), which would also explain the light hits. As the barrel pushes forward (increasing headspace) the extractor (under spring pressure pushing it against the chamber groove) goes with it, pivoting lower and lower below the edge of the chamber. The back of the extractor is curved, and the extractor slot is actually the end of a long groove cut in the bottom of the barrel, so it simply slips down as the barrel moves away from it.
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brent375hh
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Re: MG5 help needed
I am longing for MG 5 to arrive
so I read this topic interestingly
I think this is the cause of the problem
so I read this topic interestingly
I think this is the cause of the problem
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Re: MG5 help needed
I believe this is a time to reach for the steel filled Devcon Epoxy..... Place a dab in the overcut area, allow it to cure and either follow it up with a jewelers file or an appropriate drill..... There is no problem with pressures since the barell backs it up and all you are really trying to do is prevent case bulges......... If you cant get satisfactory answers from matchguns, glue it up and have a great life. FWIW, the product is a room temp cure and easily cut with even moderately dull tools........
Also, the connection between a difficult to chamber round and a misfire is this..... The round seated at its minimum inssrtion distance to close the bolt still allows a small gap between the chamber face and the forward edge of the rim..... When the firing pin hits the round, the round actually moves forward a bit and the firing pin strike looks light, it gos bang the second strike because the round is fully seated and has enough rim support to get solid primer ignition.... This is a classic toz35 problem.....
Also, the connection between a difficult to chamber round and a misfire is this..... The round seated at its minimum inssrtion distance to close the bolt still allows a small gap between the chamber face and the forward edge of the rim..... When the firing pin hits the round, the round actually moves forward a bit and the firing pin strike looks light, it gos bang the second strike because the round is fully seated and has enough rim support to get solid primer ignition.... This is a classic toz35 problem.....