gsmopar Posted November 3, 2013 Report Share Posted November 3, 2013 (edited) Reference my earlier thread for additional history: First trip to the range after changing the ejector and the problem still persists. I took pictures of the jams and I suspect that it is short stroking: After reading the CMMG barrel nut stories on this board, I figured that it would be in my best interest to tear the upper down and take a look at things. After removing the hand guard I found this: I continued with the teardown and inspection. The barrel nut came off with little effort, but I can't say that it was loose enough to allow the barrel to move: I used a mic to measure the distance from the shoulder to the gas port and then measured the gas block. I came up with a 1/16 in offset to align the holes. The barrel is drilled for the back setscrew in the gas block and this aligned with my measurements. Is this normal for a gas block, or could this be a symptom of my problem? Thanks again for all of the help! Greg Edited November 3, 2013 by gsmopar Quote Link to comment Share on other sites More sharing options...
98Z5V Posted November 3, 2013 Report Share Posted November 3, 2013 (edited) Gas block looks good, brother - nothing out of the ordinary there. You'll have some carbon blow by on stuff like that, until there's enough buildup to make a good seal. No kidding. Looks like the gas block port covered the gas port in the barrel just fine - was the gas block mounted tight? Other than that, gas system looks alright. Something in the pics made me look at the end of the gas key on the carrier - is the end of the gas key flared? Outward? Looks funny. Check how much the gas tube protrudes into the upper receiver, when you put it back together. EDIT - measure the diameter of that gas port in the barrel, while you've got it apart. Edited November 3, 2013 by 98Z5V Quote Link to comment Share on other sites More sharing options...
shibiwan Posted November 3, 2013 Report Share Posted November 3, 2013 Definitely looks like it's short stroking - mine did the same thing with XM80C's when I put in the 12-oz buffer. I did notice some blowby on my CMMG barrel, but it's towards the rear of the gas block, away from the muzzle end. Nothing abnormal. What ammo are you using? Quote Link to comment Share on other sites More sharing options...
survivalshop Posted November 3, 2013 Report Share Posted November 3, 2013 Did you do the one round in the mag fire test to see if the bolt catch works to hold the bolt back on empty mag. ? This test will tell you if your BCG is coming back far enough . It could be coming back too far & fast & not letting the empty case out of the upper receiver or the extractor is holding the spent case on the bolt face too long . Check your carrier key to make sure its tight & sealing . Checking the gas port size may give you some info , but some manufacturers have there own sizes & different sizes for different length gas systems. Also a rough or tight ,not to spec chamber may be hindering the removal of the spent case from it.( like some DPMS BBL's in the past ) There is a timing thing with semi auto systems & when they are out of timing , it disrupts different phases of the action cycling . Quote Link to comment Share on other sites More sharing options...
edgecrusher Posted November 3, 2013 Report Share Posted November 3, 2013 ^^^ with this, I would suggest trying to hook up with someone else in the az area (there's a bunch of you) and see if a heavy buffer works. Like SS said, if that thing is going too fast, it could also be causing that issue Quote Link to comment Share on other sites More sharing options...
Robocop1051 Posted November 3, 2013 Report Share Posted November 3, 2013 Have you taken apart the bolt yet? I'd be interested to know the condition of the springs inside the bolt. Quote Link to comment Share on other sites More sharing options...
gsmopar Posted November 3, 2013 Author Report Share Posted November 3, 2013 Gas block looks good, brother - nothing out of the ordinary there. You'll have some carbon blow by on stuff like that, until there's enough buildup to make a good seal. No kidding. Looks like the gas block port covered the gas port in the barrel just fine - was the gas block mounted tight? Other than that, gas system looks alright. Something in the pics made me look at the end of the gas key on the carrier - is the end of the gas key flared? Outward? Looks funny. Check how much the gas tube protrudes into the upper receiver, when you put it back together. EDIT - measure the diameter of that gas port in the barrel, while you've got it apart. Here is a pic of the key on the carrier. I read that thread comparing the gas tube length inside the upper. I'll measure that next. Definitely looks like it's short stroking - mine did the same thing with XM80C's when I put in the 12-oz buffer. I did notice some blowby on my CMMG barrel, but it's towards the rear of the gas block, away from the muzzle end. Nothing abnormal. What ammo are you using? I've used wide array of ammo types The gun shoots the heavy stuff just fine, but doesn't like 147 or similar nato rounds. This time out I was using the Winchester white box 7.62 147 grain. ^^^ with this, I would suggest trying to hook up with someone else in the az area (there's a bunch of you) and see if a heavy buffer works. Like SS said, if that thing is going too fast, it could also be causing that issue I have a 5.6 oz heavy buffer and Tubbs BCW. I've played with the carrier weights and haven't had much success. This time out I had the middle weight (steel) in the BCW. Have you taken apart the bolt yet? I'd be interested to know the condition of the springs inside the bolt. Yes. I rebuilt the bolt, replacing the ejector and spring previous to this outing. Thanks for the ideas! Keep them coming!!! Quote Link to comment Share on other sites More sharing options...
bubbasks Posted November 3, 2013 Report Share Posted November 3, 2013 I had a similar issue with mine when i built it. I started offadjusting the gas block to lowest setting for locking back and did fine single loading but once i filled the mag it constantly did the same as you have shown. All said springs but on a new set up it didnt sound right. Well after toying with it for weeks i upped the gas a half turn and it ran flawlessly. You seem to have a bit of blowby till it eventually seals. Quote Link to comment Share on other sites More sharing options...
gsmopar Posted November 3, 2013 Author Report Share Posted November 3, 2013 I had a similar issue with mine when i built it. I started offadjusting the gas block to lowest setting for locking back and did fine single loading but once i filled the mag it constantly did the same as you have shown. All said springs but on a new set up it didnt sound right. Well after toying with it for weeks i upped the gas a half turn and it ran flawlessly. You seem to have a bit of blowby till it eventually seals. I don't have an adjustable gas block (at least I don't think that it's adjustable), but I agree that it appears to be under gassed. My bolt locks back on the single shot tests as well, but on occasion it has not lock on the last round of a full magazine. Quote Link to comment Share on other sites More sharing options...
shibiwan Posted November 3, 2013 Report Share Posted November 3, 2013 (edited) I don't have an adjustable gas block (at least I don't think that it's adjustable), but I agree that it appears to be under gassed. My bolt locks back on the single shot tests as well, but on occasion it has not lock on the last round of a full magazine. It may be locking back but is it locking on the bolt face (correct) or the bolt carrier (wrong)? Are there one or two rubber rings around the extractor spring? The Winchester 147g white box is also a little underpowered, just like the XM80C. May want to take that into consideration, and compare those to other ammo to see if it's making a difference. What length buffer assembly are you using? I need someone local to test our .308 carbine length heavy buffer.... Edited November 3, 2013 by shibiwan Quote Link to comment Share on other sites More sharing options...
gsmopar Posted November 4, 2013 Author Report Share Posted November 4, 2013 (edited) It may be locking back but is it locking on the bolt face (correct) or the bolt carrier (wrong)? Are there one or two rubber rings around the extractor spring? The Winchester 147g white box is also a little underpowered, just like the XM80C. May want to take that into consideration, and compare those to other ammo to see if it's making a difference. What length buffer assembly are you using? I need someone local to test our .308 carbine length heavy buffer.... I didn't think to look to see if it was locking on the bolt face or carrier. I will take note next time. I remember rubber o-rings on the extractor, but I'm not sure if it was 1 or 2. I can check that easy enough. I'm using a carbine length buffer and am located in Arizona (Gilbert). Edited November 4, 2013 by gsmopar Quote Link to comment Share on other sites More sharing options...
washguy Posted November 4, 2013 Report Share Posted November 4, 2013 Yep the white box Federal is a lil underpowered... take the upper off...hold the muzzle down with the dust cover open....drop the bcg and observe what happens....does it hang on he gas tube or anything like that? it should just about go into battery give or take Wash Quote Link to comment Share on other sites More sharing options...
shibiwan Posted November 4, 2013 Report Share Posted November 4, 2013 I didn't think to look to see if it was locking on the bolt face or carrier. I will take note next time. I remember rubber o-rings on the extractor, but I'm not sure if it was 1 or 2. I can check that easy enough. I'm using a carbine length buffer and am located in Arizona (Gilbert). I'm out in Queen Creek/Mesa so we are close. Give me a few days...I'll whip up a carbine buffer and you can test it. Quote Link to comment Share on other sites More sharing options...
washguy Posted November 4, 2013 Report Share Posted November 4, 2013 i always go back to basics if theres a problemo which buffer spring? if its the tubbs flatwound i use them... with no probs but if you have a cheapo buffer spring and just a regular ol buffer for the type stock you have I would put those in....also get rid of the tubbs cws weights for testing purposes they can mess up timing and cycling which is what you have :) Wash Quote Link to comment Share on other sites More sharing options...
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