Viggen Posted August 23, 2009 Share Posted August 23, 2009 (edited) Here is the situation. A DPMS upper - 16" barrel with a full length gas tube. Accuracy is supurb. I got lucky and when shooting groups it stayed under .5" at 100 yds. At this age and with my eyes I never expected that with anything. Anyway, the reliability just isn't there - bolt doesn't reliable pick up another round. After trouble shooting the various possibilities - magazines, chamber, bolt, gas tube, etc., etc., it seems to come down to an oversized gas port or hole or whatever it is called in the barrel. And that's what the gunsmith tells me. I tend to believe him since he does a lot of good AR work. So it's new barrel time but I don't want to lay out that much money, really I can't right now, and this barrel shoots real well. I was wondering if maybe one of the adjustable gas blocks like what JP makes could be used to adjust gas flow in place of replacing the barrel and a smaller gas port. Has anyone done this sort of thing when working around this sort of situation? Edited August 23, 2009 by Viggen Link to comment Share on other sites More sharing options...
el pres Posted August 23, 2009 Share Posted August 23, 2009 If thats the case then an adjustable gas block should work ?? Link to comment Share on other sites More sharing options...
Glockcomma Posted August 23, 2009 Share Posted August 23, 2009 It seems that the consensus is that a rifle length gas system is to long for a 16" barrel, not enough dwell time. Link to comment Share on other sites More sharing options...
smokshwn Posted August 23, 2009 Share Posted August 23, 2009 As nice as it would be to simply strap on an adjustable gas block I am pretty sure the problem lies in the rifle lenght system on a 16" gun. You are not getting too much gas (hole to big) you are not getting enough gas which is caused by either the port being too small or not enough dwell time which is the time between when the bullet passes the port to when the bullet exits the barrel. Link to comment Share on other sites More sharing options...
Mickster Posted August 23, 2009 Share Posted August 23, 2009 One of my setups is the DPMS 16" long gas barrel, JP adjustable gas block, light weight carrier and buffer. I have the gas tuned to reliably work with Wolf 55's (known to be underpowered ammo) but I normally shoot hotter mil spec or reloads in it. It has been a flawless performer for several years (couple thousand rounds probably) with no functioning issues whatsoever. No premature wear on the extractor or anything else. It handles very nicely too. Link to comment Share on other sites More sharing options...
mpeltier Posted August 23, 2009 Share Posted August 23, 2009 Ive seen Mickster's 16" run and it is extremely reliable. Viggen, What ammo? What stock and buffer are you running? What carrier? I would be surprised if it were the bbl. Link to comment Share on other sites More sharing options...
Viggen Posted August 23, 2009 Author Share Posted August 23, 2009 Ive seen Mickster's 16" run and it is extremely reliable.Viggen, What ammo? What stock and buffer are you running? What carrier? I would be surprised if it were the bbl. All factory DPMS parts - upper and lower. Factory bolt and bolt carrier. All ammo, any weight, any brand - factory or reloads, results are the same. There is no way that I know to increase the dwell time and there is no way the gas port is too small. That leaves the choice of metering the gas with an adjustable gas block. I am aware that a full length system on a 16" system is not the way to go, just what I have in front of me right now. I need a way around the problem without putting out for a new barrel. Link to comment Share on other sites More sharing options...
Glockcomma Posted August 23, 2009 Share Posted August 23, 2009 Can a gas port be plugged and a new one drilled at the mid or carbine length? Link to comment Share on other sites More sharing options...
mpeltier Posted August 23, 2009 Share Posted August 23, 2009 (edited) Ive seen Mickster's 16" run and it is extremely reliable.Viggen, What ammo? What stock and buffer are you running? What carrier? I would be surprised if it were the bbl. All factory DPMS parts - upper and lower. Factory bolt and bolt carrier. All ammo, any weight, any brand - factory or reloads, results are the same. There is no way that I know to increase the dwell time and there is no way the gas port is too small. That leaves the choice of metering the gas with an adjustable gas block. I am aware that a full length system on a 16" system is not the way to go, just what I have in front of me right now. I need a way around the problem without putting out for a new barrel. Be more specific, Is it an A2 rifle stock or a telescoping carbine stock??? What buffer, stock rifle type or a carbine standard, H, etc.??? What I am getting at is the weight of the carrier/Buffer has much to do with reliability in your case. I bet you are running a pretty heavy carrier/buffer set up. take some weight out with a light weight buffer and possibly the carrier and it will probably be more reliable. If i had specific details of exactly what you got now I could suggest something to try that might be less expensive/eisier than a new bbl. Metering the gas is not your problem, as an adjustable gas block aint gonna give back something you aint got (enough gas) so you need to help it by reducing the mass the existing gas has to overcome to move the bolt carrier/buffer in a proper manner. Edited August 23, 2009 by mpeltier Link to comment Share on other sites More sharing options...
Viggen Posted August 23, 2009 Author Share Posted August 23, 2009 Ive seen Mickster's 16" run and it is extremely reliable.Viggen, What ammo? What stock and buffer are you running? What carrier? I would be surprised if it were the bbl. All factory DPMS parts - upper and lower. Factory bolt and bolt carrier. All ammo, any weight, any brand - factory or reloads, results are the same. There is no way that I know to increase the dwell time and there is no way the gas port is too small. That leaves the choice of metering the gas with an adjustable gas block. I am aware that a full length system on a 16" system is not the way to go, just what I have in front of me right now. I need a way around the problem without putting out for a new barrel. Be more specific, Is it an A2 rifle stock or a telescoping carbine stock??? What buffer, stock rifle type or a carbine standard, H, etc.??? What I am getting at is the weight of the carrier/Buffer has much to do with reliability in your case. I bet you are running a pretty heavy carrier/buffer set up. take some weight out with a light weight buffer and possibly the carrier and it will probably be more reliable. If i had specific details of exactly what you got now I could suggest something to try that might be less expensive/eisier than a new bbl. Metering the gas is not your problem, as an adjustable gas block aint gonna give back something you aint got (enough gas) so you need to help it by reducing the mass the existing gas has to overcome to move the bolt carrier/buffer in a proper manner. Stock A2 Rifle type, buffer is whatever DPMS put in. Might be time to trade for a decent bolt action......... Link to comment Share on other sites More sharing options...
mpeltier Posted August 24, 2009 Share Posted August 24, 2009 The buffer you are using now is over 5 oz. Either put in a JP Buffer or swap the weights in it now for some pieces of aluminum that will bring it down to about 3.0 oz. And put a generous amount of a good slippery grease on the buffer spring. If that by itself does not cure your problem try a light carrier. Link to comment Share on other sites More sharing options...
gotm4 Posted August 24, 2009 Share Posted August 24, 2009 Here is the situation.A DPMS upper - 16" barrel with a full length gas tube. Accuracy is supurb. I got lucky and when shooting groups it stayed under .5" at 100 yds. At this age and with my eyes I never expected that with anything. Anyway, the reliability just isn't there - bolt doesn't reliable pick up another round. After trouble shooting the various possibilities - magazines, chamber, bolt, gas tube, etc., etc., it seems to come down to an oversized gas port or hole or whatever it is called in the barrel. And that's what the gunsmith tells me. I tend to believe him since he does a lot of good AR work. So it's new barrel time but I don't want to lay out that much money, really I can't right now, and this barrel shoots real well. I was wondering if maybe one of the adjustable gas blocks like what JP makes could be used to adjust gas flow in place of replacing the barrel and a smaller gas port. Has anyone done this sort of thing when working around this sort of situation? You can have a good machinist gunsmith fix the gas port. A 16" carbine length gas system should have a gas port of .063" and no bigger than .067" This is from Randall at AR15barrels.com: Remove the front sight base. Drill down about 0.15" to 0.175" with a #43 drill bit. Tap this top 2/3 of the barrel wall thickness 4-40. Install a 4-40 x 1/8 setscrew firmly into the port until it stops against the shoulder you left at the bottom. Verify that the setscrew is about 0.025" to 0.050" below flush from the surface of the gas block seat. Peen the top of the setscrew so it's locked into place. Drill down through the setscrew with a 1/16" drill bit. Re-assemble the barrel. Link to comment Share on other sites More sharing options...
benny hill Posted August 24, 2009 Share Posted August 24, 2009 Make sure you have the bolt & carrier WET with plenty of oil.Inside more than outside. Link to comment Share on other sites More sharing options...
SHELLFISH17 Posted August 24, 2009 Share Posted August 24, 2009 I agree with mpeltier, buy a JP lightened bolt carrier and buffer and that should help the small amount of gas you have cycle better due to less weight of mass its moving. You could also barrow a friends carbine lower to see if just the buffer and spring difference would help. Link to comment Share on other sites More sharing options...
stgdz Posted August 25, 2009 Share Posted August 25, 2009 This is the one with the HBAR style barrel correct, if so how heavy is it? Doesn't benny cooley run one of these also? He said there wasn't many issues with his. Link to comment Share on other sites More sharing options...
dmshozer1 Posted August 26, 2009 Share Posted August 26, 2009 Here is the situation.A DPMS upper - 16" barrel with a full length gas tube. Accuracy is supurb. I got lucky and when shooting groups it stayed under .5" at 100 yds. At this age and with my eyes I never expected that with anything. Anyway, the reliability just isn't there - bolt doesn't reliable pick up another round. After trouble shooting the various possibilities - magazines, chamber, bolt, gas tube, etc., etc., it seems to come down to an oversized gas port or hole or whatever it is called in the barrel. And that's what the gunsmith tells me. I tend to believe him since he does a lot of good AR work. So it's new barrel time but I don't want to lay out that much money, really I can't right now, and this barrel shoots real well. I was wondering if maybe one of the adjustable gas blocks like what JP makes could be used to adjust gas flow in place of replacing the barrel and a smaller gas port. Has anyone done this sort of thing when working around this sort of situation? Viggen, click on page two to read what I had to say about 16 inch rifle length barrels and trust me, it is the truth! I have the exact same barrel and yes, mine is a tact driver too! I would bet that a carbine buffer spring in your gun would make you a happy camper! Oh yeah,my gas port is .100. Another thing, do not put heavy grease on the buffer spring as it will slow the action down. Link to comment Share on other sites More sharing options...
Tyler Payne Posted August 27, 2009 Share Posted August 27, 2009 It sounds like you need more gas. Your port should be at .113 or a #33 drill bit Link to comment Share on other sites More sharing options...
Storm52 Posted August 29, 2009 Share Posted August 29, 2009 I'd start with a standard carbine buffer for about $19 and see if that solves your issue. If not I would go to a lighter (carbine) BCG. Link to comment Share on other sites More sharing options...
Viggen Posted September 29, 2009 Author Share Posted September 29, 2009 As the world churns.... It turns out that it's not really a gun problem. It's an operator/ammo putter togetherer problem. At the advice of son I changed powder, obviously, it couldn't be the powder, and so far it's running 100%, and this after I was about to walk out back and use the chopsaw to just be rid of the problem. I had been running 2015BR - wonderful powder that metered great, gave marvelous accuracy, but the gun didn't like it. Switched to Ramshot TAC - meters great, great accuracy, gun likes it.\ (Pardon me while I go into a closet and scream) Link to comment Share on other sites More sharing options...
STIGUY Posted September 30, 2009 Share Posted September 30, 2009 As the world churns....It turns out that it's not really a gun problem. It's an operator/ammo putter togetherer problem. At the advice of son I changed powder, obviously, it couldn't be the powder, and so far it's running 100%, and this after I was about to walk out back and use the chopsaw to just be rid of the problem. I had been running 2015BR - wonderful powder that metered great, gave marvelous accuracy, but the gun didn't like it. Switched to Ramshot TAC - meters great, great accuracy, gun likes it.\ (Pardon me while I go into a closet and scream) That's great....I have a 16" barrel with a rifle length gas tube. I do have a JP lightened carrier and never have those problems with function. However, I don't reload right now. Did you state that your reloading in your first post? Link to comment Share on other sites More sharing options...
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