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Posted: 5/12/2013 6:20:34 PM EDT
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The gas tube end that enters the carrier key is getting chewed up. It kind of looks like its got arc weld burns on it.
This is a new Fail Zero carrier and gas key. New gas tube Gas tube is not bound and has some wiggle room passing thru the upper and barrel nut. When built everything moved freely and smoothly. After first 15 rounds BCG locked up right where the gas tube enters the key. I should say this is a total new set-up. I fired 5 rounds, pulled off the upper and BCG, cleaned completely, fired 5 more, repeat. Fire 5 more BCG locks on last round. I got it apart, pulled out the bolt and installed just the carrier and charging handle. Sure enough the gas key had started locking up on the gas tube. Thru the first 2 sets of 5 rounds there was no bind at all, in fact super smooth and easy movement into battery. Now the gas tube looks like it has arc weld marks on it, and binds in the carrier key when inserting into the carrier key, both parts in hand not installed in the gun. Can I use some 800 wet/dry to smooth it out again? What would cause this type of damage? Specs. Northtech Defense AR15 Billet Lower Reciever Vltor MUR Upper reciever PSA Gen 2 MOE LPK Magpul STR Stock Kit FDE BCM H - Buffer DPMS 6.8 SPC Bolt Fail Zero Bolt Carrier NIBx Cam Pin DPMS Firing Pin MI Gen 2 SS-Series 12in Rail FDE Mil-spec Buffer Tube 7075 BCM Charging Handle Mod4 Magpul AFG2 Front Grip FDE Magpul MBUS Rear Gen 2 FDE Magpul MBUS Front Gen 2 FDE Bison Armory Recon Barrel 6.8 SPCII Stainless Seekins Precision LoPro Adjustable Gas Block Seekins Precision ATC Muzzle Brake KNS Trigger Pins Gen2 Mod2 FDE Tapco End Plate Sling Adapter Surefire M952 Weapon Light Ammo fired was Hornady Match 110 grain BTHP |
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The beveled entry section of the gas tube should be smooth and clean. If needed, polish out it, including inner lip edge of the believe as well. Also note here, if the inside of the bevel has a bur from production, remove it as well. As for the inner channel, do don't want to remove much of it, but the walls of the channel can be slightly polished out if needed with say a Q tip and some lapping compound. Just remember to flush out all the lapping compound fully before you put the bolt back in.
Once you have the entry of the key cleaned up, remove the bolt off the B/C, and dry fit the carrier alone to the upper receiver to see if the gas tube needs to be tweaked above the middle of the barrel to correctly align the gas tube end with the key. |
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Quoted:
The beveled entry section of the gas tube should be smooth and clean. If needed, polish out it, including inner lip edge of the believe as well. Also note here, if the inside of the bevel has a bur from production, remove it as well. As for the inner channel, do don't want to remove much of it, but the walls of the channel can be slightly polished out if needed with say a Q tip and some lapping compound. Just remember to flush out all the lapping compound fully before you put the bolt back in. Once you have the entry of the key cleaned up, remove the bolt off the B/C, and dry fit the carrier alone to the upper receiver to see if the gas tube needs to be tweaked above the middle of the barrel to correctly align the gas tube end with the key. Its almost like the beveled entry section of the gas tube got bigger somehow after firing 15 rounds. I don't see how that's possible. I will try the q-tip and lapping compound to clean up the inside of the carrier key as well. I am just at a loss as to why this started happening, as during the first 2 tear downs I looked at the gas tube bevel and all looked fine. Plus as I say I did hand cycle the upper with it off numerous times. I would guess I hand cycled the BCG at least 100 times trying to wear the parts in together before firing the first time. |
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Quoted:
Quoted:
The beveled entry section of the gas tube should be smooth and clean. If needed, polish out it, including inner lip edge of the believe as well. Also note here, if the inside of the bevel has a bur from production, remove it as well. As for the inner channel, do don't want to remove much of it, but the walls of the channel can be slightly polished out if needed with say a Q tip and some lapping compound. Just remember to flush out all the lapping compound fully before you put the bolt back in. Once you have the entry of the key cleaned up, remove the bolt off the B/C, and dry fit the carrier alone to the upper receiver to see if the gas tube needs to be tweaked above the middle of the barrel to correctly align the gas tube end with the key. Its almost like the beveled entry section of the gas tube got bigger somehow after firing 15 rounds. I don't see how that's possible. I will try the q-tip and lapping compound to clean up the inside of the carrier key as well. I am just at a loss as to why this started happening, as during the first 2 tear downs I looked at the gas tube bevel and all looked fine. Plus as I say I did hand cycle the upper with it off numerous times. I would guess I hand cycled the BCG at least 100 times trying to wear the parts in together before firing the first time. Where did you get the gas tube? Recently, I've seen some at a local gun store that appeared suspect and the material seemed to be too soft. |
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Quoted:
Quoted:
Quoted:
The beveled entry section of the gas tube should be smooth and clean. If needed, polish out it, including inner lip edge of the believe as well. Also note here, if the inside of the bevel has a bur from production, remove it as well. As for the inner channel, do don't want to remove much of it, but the walls of the channel can be slightly polished out if needed with say a Q tip and some lapping compound. Just remember to flush out all the lapping compound fully before you put the bolt back in. Once you have the entry of the key cleaned up, remove the bolt off the B/C, and dry fit the carrier alone to the upper receiver to see if the gas tube needs to be tweaked above the middle of the barrel to correctly align the gas tube end with the key. Its almost like the beveled entry section of the gas tube got bigger somehow after firing 15 rounds. I don't see how that's possible. I will try the q-tip and lapping compound to clean up the inside of the carrier key as well. I am just at a loss as to why this started happening, as during the first 2 tear downs I looked at the gas tube bevel and all looked fine. Plus as I say I did hand cycle the upper with it off numerous times. I would guess I hand cycled the BCG at least 100 times trying to wear the parts in together before firing the first time. Where did you get the gas tube? Recently, I've seen some at a local gun store that appeared suspect and the material seemed to be too soft. From Bison Armory with the barrel. His stuff is supposed to be top notch. |
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