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Posted: 6/18/2016 11:37:54 AM EDT
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OK - just completed my coyote hunting rig - its in a used S&W lower with a good unmarked modular trigger. The upper is a wilson barrel with colt upper parts assembled by a ex USMC armoror. The headspace has been checked and rechecked as well as ramp polishing -it has M4 feedramps.
The issue is a "Deadbolt" bolt carrier group bought from ground zero precision - it just does not want to go into battery 100% of the time it will run about 70% and jam the rest - the forward assist will not put it into battery either. I exchanged bolts from my other two AR's and tried a friends and the gun ran 100%. The ad for the bolt said "100 functional" but may have minor cosmetic blems. But the bolt definently needs more force to move in the carrier than the other bolts we examined. The good folks at Ground Zero Precision will not respond to many call/e-mails so no help there. Would the next step be to polish the bolt? Maybe Buff it? I hate to be changing bolt carrier groups around every time we go to shoot especially since I put $$ into this one. |
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Since you have the old working B/C, swap out the working bolt on the new carrier with key, and determine which is the problem.
If the new carrier is having problems (and you have dry fitted just the carrier with key and no bolt in the upper receiver to make sure that the gas tube is aligned correctly with it key and key not too wide to bind in the upper receiver slot), then suspect that key is not sealing correctly to the top of the carrier to cause a gas leak and the problem at hand. If the other way, with the new bolt in a used working carrier with key and you have problems, then we know that is the bolt that has the problem. Go and no go head space gauges make quick work of checking to make sure that the head spacing it correct with the bolt, but it could be other problems as well. In regards to other problems, could be that the ejector is binding it's channel and you may have to pull the ejector to clean up that problem. Could be that the extractor rim releif channel is not milled correctly, as well as the rim entry taper and it stop pad, not allowing the round to glide down the extractor section to allow the case rim to glide past it and lock in place on the face of the bolt. Also, and this is becoming more and more common, a O ring or defender installed around the extractor spring, with it causing too much tension on the extractor for the case rim to open it up on loading to glide into place on the bolt face isntead. As for back to the bolt, do not screw around with it trying to adjust the head spacing between it and the bolt until you know the head spacing dimension to begin with, and if the problem is the bolt face recess, or the lugs dimensions instead. If you just want to check the bolt demensions to start with, 
Short of having the needed gauges, and the needed machinery (lathe in this case), there is not way to rework a bolt reliably to end up with the needed head spacing instead. In regards to the carrier if you have a carrier key leak, the key bolts have to be replaced with new ones once they are removed, then you get into having to lap the new key into the carrier as well to solve the gas leak problems when the key is re-installed. Same goes for if the key is too wide and binding in the upper receiver slot, hence need to pull the key to lap plate the sides of it to narrow it down. |
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Quoted:
Short of having the needed gauges, and the needed machinery (lathe in this case), there is not way to rework a bolt reliably to end up with the needed head spacing instead. Not just a lathe, but one with a tool post grinder. And, it will have to be able to maintain that .0005" same plane requirement for the lugs and the .0015"parallelism with the face of the bolt..... So, your Grizzly 7 inch lathe probably ain't gonna' be up to it. |
| Ok will do the switch overs with those components and check the dimensions. I have access to advanced machine tools if needed but my suspicion is that the friction of the bolt body in the carrier is too high due to the finish. The barrel is a .223 Wylde chamber shouldn't matter according to the maker? |
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Quoted:
Ok will do the switch overs with those components and check the dimensions. I have access to advanced machine tools if needed but my suspicion is that the friction of the bolt body in the carrier is too high due to the finish. The barrel is a .223 Wylde chamber shouldn't matter according to the maker? The bolt not moving in the carrier smoothly is more of a problem we see with a mcfarland gas ring that have not mated in yet. If you suspect the bolt is too tight in the carrier, the rotate walk/glide the rings off the bolt with your thumb nail one at a time to not destroy them, and dry fit the bolt into the carrier to check for binding. Here, your checking for not only the glide band about the center of the bolt to be the correct diameter to allow such, but the bugle section on the tail of the bolt being smoothing radius milled so the bolt tail is not binding on the carrier gas section channel lip as well. Hence if the bolt only binds when you push it all the way in, suspect that the problem is with the tail of the bolt where it first flairs outward to create the ring groove section. If the bolt glides smoothly without the gas rings, then double check the channel for the gas ring on the bolt to make sure it clean and smooth as well. Hence on a plated bolt, may have some plating build up crap in the ring groove that you have have to clean (just chuck the tail of the bolt up in a drill and spin sand/file the channel to clean it up. Now on the gas rings, they are stamp produced, meaning that the outer and inner edges on one side will be smooth and the other side edges sharp isntead. So when you install rings on a bolt, all the sharp side edges will be facing the tail of the bolt, and the round edges will be facing the lug side of the bolt. Hence we want all the sharp edge facing the direction of the gas pulse, so they seal better. Lastly, the correct ring test for a bolt is to pull the bolt all the way out, then stand the carrier on it back side downwards, and the bolt upwards, and confirm that the bolt will stay up under it own weight. Time and time again I keep seeing that people thinking that the gas ring test is to hold the carrier weight up , and they are dead wrong. Hence once the rings do mate into into the carrier after a few hundred rounds, they are just supposed to seal against the carrier section with minimal binding instead. So when they do the Incorrect "rings holding the carrier weight test, this only tells them that the rings have not mated in yet, and will actual leak worse than the correctly mated in rings they just pulled of the bolt when the rings where supporting the bolts weight isntead. So again, the correct ring test is for the rings to just hold the weight of the bolt up in the carrier alone (bolt skyward), and when the rings will not longer hold the weight of the bolt up in the carrier since they are worn too far away, then it time to replace the rings. |
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