Bfalcon00 Posted July 4, 2011 Report Share Posted July 4, 2011 I have a DPMS upper and lower mated to a Fulton Armory 20 inch barrel with a rifle gas system. I was having some trouble with it being over gassed and the bolt slamming so i installed a JP railed adjustable gas block. That cleared everything up and the rifle runs just fine except the bolt will not lock back after the last round is fired. The bolt will lock back just fine if you use an empty mag and the charging handle to cycle the bolt. Im guessing the bolt is just cycling too fast but I dont really know. Any ideas? Oh and the bolt catch is a phase 5 battery assist, but the problem doesnt go away if you install a normal bolt catch. Quote Link to comment Share on other sites More sharing options...
imschur Posted July 4, 2011 Report Share Posted July 4, 2011 Are you certain the buffer and buffer spring are for 308? Quote Link to comment Share on other sites More sharing options...
JMoto Posted July 4, 2011 Report Share Posted July 4, 2011 Did you adjust the gas flow to try and fix this? If you have the gas turned too low it will not cycle the carried back far enough to lock the bolt back. Try adding a little bit more gas and see if that fixes the issue. When using and adj gas block you want to set it up so the rifle runs with the lightest load you will be shooting from the gun. In addition to this, the way you shoot the gun during adjustment will also effect it. You provide a different amount of resistance to the rifle in different shooting positions. Meaning your body will be absorbing the recoil differently and this will have an effect on the cycling of the weapon. Quote Link to comment Share on other sites More sharing options...
Bfalcon00 Posted July 4, 2011 Author Report Share Posted July 4, 2011 Im certain the buffer and spring is for a 308 swapped out with my other 308 to be sure. I turned the gas block for off all the way to full open just to be sure used 1/4 turns each adjustment. The bolt cycles just fine and will load ammo from the mag it just wont lock back after the last round. Quote Link to comment Share on other sites More sharing options...
Jgun Posted July 4, 2011 Report Share Posted July 4, 2011 I thought that when you turn the gas adjustment in all the way on the JP block, it shuts off the gas completely and makes the gun a single shot? If that's correct and your's is cycling with it all the way closed, wouldn't that indicate something wrong with the GB (maybe not threaded deep enough? Can you adjust your gas impulse down low enough that the gun doesn't cycle? Quote Link to comment Share on other sites More sharing options...
JMoto Posted July 4, 2011 Report Share Posted July 4, 2011 How much clearance do you have between the bolt face and the bolt hold open? You should have about 1/8 of an inch. Quote Link to comment Share on other sites More sharing options...
survivalshop Posted July 5, 2011 Report Share Posted July 5, 2011 Can't see how you could be over gassed with a rifle length gas system ,unless you had miss matched components (buffer /spring/receiver extension ).Its sounds like you are under gassed now (adjustment) or you have binding components . If you can charge the BCG & it holds back the bolt correctly with empty mag., with no binding , the system components are OK. Are you sure the gas block is on correctly ?I have a 20" Fulton bbl. & no problems. Quote Link to comment Share on other sites More sharing options...
JMoto Posted July 5, 2011 Report Share Posted July 5, 2011 If you have proper clearance for the bolt hold open and you have a tested with the gas full open you may have th gas block misaligned. Most people assume the gasblock mounts right up to the shoulder but in many times this is not the case (if your barrel even has a shoulder). You should check there to make sure. Quote Link to comment Share on other sites More sharing options...
Turbotezza Posted July 5, 2011 Report Share Posted July 5, 2011 I also think that you are now undergassed. I once had a gas key clog up on me and it caused the rifle to short stroke. I soaked and cleaned it up and presto! A fully functional rifle again. Quote Link to comment Share on other sites More sharing options...
Bfalcon00 Posted July 8, 2011 Author Report Share Posted July 8, 2011 I got the proper clearance on the bolt about 1/8 inch so thats not it. I didnt think about the gas block not being seated right ill check that and get back to ya. The barrel does have a shoulder for the gas block to seat against and i guess i just assumed it would fit exact. When i turn the adjustable gas block all the way down the bolt doenst cycle and the rifle functions as a single shot rifle. The only other thing i can think of is when i installed the gas block, the gas block adjustment screw would not quite clear the gas tube, so i took a file to it and took of a little material.... Quote Link to comment Share on other sites More sharing options...
98Z5V Posted July 8, 2011 Report Share Posted July 8, 2011 The only other thing i can think of is when i installed the gas block, the gas block adjustment screw would not quite clear the gas tube, so i took a file to it and took of a little material....That would leave you over-gassed, if anything. If you can still thread it in enough to shut the gas system down completely, then taking material off the length of that adjusting screw didn't harm you at all. <thumbsup> Quote Link to comment Share on other sites More sharing options...
Jgun Posted July 8, 2011 Report Share Posted July 8, 2011 Just wondering here, I may be asking stupid questions but since we're trying to diagnose the problem based on you description certain things that are obvious to the person holding the gun are not clear to me. You say that with the gas system opened up all the way, the gun cycles properly, but still does not Lock back on an empty mag. You also state that changing the bolt release lever has no effect on the problem. Have you ruled out that, as stated above, it's definitely not under gassed? Sometimes the bolt carrier has enough gas to strip and load the rd but is not going back far enough to give the bolt catch a chance to engage the front of it. Just throwing ideas out here, but have you tried different mags from the same, and from different mfgs? Do you have some ammo that you know to be loaded hotter to give a greater gas impulse? I don't know what your parts resources are from your own extra parts, and from friends, but if you have access to different parts maybe you could try a different BCG or buffer or spring, Maybe that CWS that the members have spoken of. I'm pretty much out of ideas on what else could be causing your trouble. Once you figure it out, your going to have to post it so as to increase our base of knowledge here. Quote Link to comment Share on other sites More sharing options...
weaponizer Posted July 8, 2011 Report Share Posted July 8, 2011 I read this several times and i haven't seen these addressed:1. Have you tried different ammo?2.Have you tried a different mag?Try this to see if the gastube is aligned, take out bolt and let the carrier drop(muzzle down) on its own weight into the gastube...Are you using reloads?, tight chamber but its cycling to shoot but now enough power to hold the bolt open...Just my .02.. Quote Link to comment Share on other sites More sharing options...
survivalshop Posted July 9, 2011 Report Share Posted July 9, 2011 I have a DPMS upper and lower mated to a Fulton Armory 20 inch barrel with a rifle gas system.Never heard of a problem with there bbls. ,no tight or rough chamber . I was having some trouble with it being over gassed and the bolt slamming What kind of slamming ? closing ? , recoil ?Sounds more like wrong buffer &or spring .so i installed a JP railed adjustable gas block. That cleared everything up and the rifle runs just fine except the bolt will not lock back after the last round is fired. The bolt will lock back just fine if you use an empty mag and the charging handle to cycle the bolt. Put on round of milspec ammo in a mag. & fire it to see if the BS works .If not , try ,as stated above , a different manufactures mag or a different one . Im guessing the bolt is just cycling too fast but I dont really know. Any ideas? Oh and the bolt catch is a phase 5 battery assist, but the problem doesnt go away if you install a normal bolt catch.Is the BS that was in there one for a 308 ?The alignment of the gas tube will mostly effect bolt closing, you don't seem to have that problem . Run this BCG wet, keeping lube out of the chamber.Have you tried the original gas block to test bolt hold open ? Quote Link to comment Share on other sites More sharing options...
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