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bolt carrier and semi sear problem

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CavTrooper
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bolt carrier and semi sear problem

Postby CavTrooper » Sat Dec 03, 2016 9:52 pm

I finally got the 34 running this week, ran about 30 rds first time and another 100 before it quit. Got it home and disassembled to find that the semi sear was not latching when trying to cock the bolt. Turns out that the sear shoulder outer diameter had begun to hammer into the step in the bolt carrier and actually had upset metal on the sear shoulder so that it set too far forward to engage the lever when cocking. The step in the carrier is bored to .600" and the sear shoulder is approx. .640" just enough that when the firing pin spring is released, the sear shoulder is supposed to be stop on the carrier step which is so close in dia. that it starts to wedge in and upset metal on the sear. I check the print that TNW sent with the kit and it clearly shows bore dia. of step to .600". I measured the smaller dia. of the sear and it's around .45". I wonder is the print has a wrong dimension. I decided to turn an bushing with a .5' dia. thought hole and bored out the rear of the carrier to .75" just deep enough that the bolt would clear the bushing on the front side and pressed the bushing in and tig welded it to secure. I then milled the slot in for the sear lever and it works great, much more step for the shoulder to rest on and carry the spring load when the sear is released. I had to dress the sear outer dia. to remove the burr that had been created also. I made the bushing out of 4140 and heat treated it for good measure before pressing and welding in place. I am using an original fp spring also and 11mm booster cone. Any one else seen this problem? Now back to the range for more tests and burn some ammo.

messerschmittfan
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Re: bolt carrier and semi sear problem

Postby messerschmittfan » Sun Dec 04, 2016 3:43 pm

Had a sear break off on me last weekend, gun fired less than 20 times. First problem I have had with the TNW bolts other than minor adjustments. I will be sending back to TNW for replacement. It looks like the metal on the sear is way too thin. Photographs attached Harry
Attachments
IMG_1463.JPG
IMG_1462.JPG

CavTrooper
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Re: bolt carrier and semi sear problem

Postby CavTrooper » Sun Dec 04, 2016 10:21 pm

Did TNW do the conversion on your bolt? Interesting that the print vs their machining for the relief cut on the back are different. I would be curious to see a shot of the step inside the carrier where the semi sear seats. That's where I had my problem. I'm hoping the sear holds up, $140 for a new one would suck.
CT

messerschmittfan
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Re: bolt carrier and semi sear problem

Postby messerschmittfan » Mon Dec 05, 2016 2:28 pm

I had them do three bolt conversions a couple of years ago so I would have an extra for each gun and in looking at them each one is a bit different at the rear. I have to go to an appointment but if I get a chance later (meaning remember) I will take some photographs of them. Harry

CavTrooper
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Re: bolt carrier and semi sear problem

Postby CavTrooper » Mon Dec 05, 2016 9:53 pm

Thanks Harry, I just would like a picture of the inside of the carrier where the semi sear seats, view looking down the bore from the rear would be great, if you have time.
Larry


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