View Full Version : Bolt won't lock on last round, input and suggestions!
Hey fellas, never really posted. But I've gotten alot of good info off this site. And honestly, I trust the opinions of some on this site better than anyone I could probably find locally.
I have a DDV7 complete upper w/ low profile gas block, mid length gas tube. And a PSA complete lower. That's has a standard spring and a DD H buffer. Anyway the rifle has ran flawless thru 1000 rounds. At about the 700 round mark I noticed the ejection pattern was changing. Because I was picking up alot less brass at the range (almost a foward ejection).
Well last trip to the range the bolt stopped locking on the last round of an empty mag. Cleaned, checked the bolt relubed. Same problem. The mags I used had previously functioned fine. And I was shooting federal xm193. Bolt locks back manually on those same mags. Put oil on the gas key and blew on it, no bubbles. Carrier key isn't loose, extractor and gas rings look fine. Gas tube in the receiver and on the barrel look lined up.
Now there is some new wear on the face of the hammer. And there is corresponding new wear on the bottom of the carrier itself. Now when I was shooting. I used the mag as a monopod. But have read this is ok? I haven't contacted DD yet because think my upper maybe fine. But can anyone tell me what the heck it going on with my gun? Thanks any input would be greatly appreciated ;)
I'd try an H3. Sounds like the bolt is outrunning the follower... (excessive bolt speed). Judging by the forward ejection and no lock back... my bet is an H3 will fix you up.
Thanks for the reply. So skip the H2 buffer an go with an H3? Also should this remedy my issue. Is that putting a bandaid on what is the underlying issue of an overgassing gun? Can a rifle go from functioning, to overgassing from basic use. Then have a heavier buffer put in and problem solved? I may be over thinking this, lol
Before doing anything, place a single round in the mag, load it into the rifle, fire it and see if the bolt locks back. If not, your AR is short stroking and it's time to look for a gas leak. Start by checking the torque on the gas key screws by tightening them to the maximum torque with a torque wrench. It will show you if the screws are loose, have a sheared head or if they are stretched or stripped
Cool, yeah I read about the single round in the chamber to check for short stroking. I did try a carbine buffer that came with the lower, and that didn't help at all. I'm heading to the range on wednesday. I will try it out. I'm thinking I should just give DD a call as well. Just to see what they think. But I'll probably do that after my range test. Again thanks for the replies gentlemen. I'm never disappointed by the quality of instruction that is given on this site
NickySantoro
04-21-15, 08:26
Is there a possibility the gas tube roll pin has failed, allowing the gas tube to shift slightly out of alignment?
A few pics may help. This is what the gas block looks like. Also note the new wear on the face of the hammer. And the corresponding new wear on the left side of the carrier. Also I noticed my last time to the range. The first few rounds I belived keyholed, and I had a POI shift. Another thing is when I put an empty mag in and pull the charging handle. It comes out a bit then I've really gotta yank it back. After the hammer is engaged the charging action becomes much easier to pull. And I can smell metal rubbing together alot after multiple charges. :confused:
BufordTJustice
04-21-15, 11:39
A few pics may help. This is what the gas block looks like. Also note the new wear on the face of the hammer. And the corresponding new wear on the left side of the carrier. Also I noticed my last time to the range. The first few rounds I belived keyholed, and I had a POI shift. Another thing is when I put an empty mag in and pull the charging handle. It comes out a bit then I've really gotta yank it back. After the hammer is engaged the charging action becomes much easier to pull. And I can smell metal rubbing together alot after multiple charges. :confused:
Your gas tube roll pin appears to have checked out. I don't see it at all in the picture, though I'm on my phone.
Also, your barrel extension feed ramps appear to be protruding beyond the ramps in the lower.
The POI shift indicates the possibility of a loose barrel nut, loose muzzle device, or maybe a structural failure in the upper or barrel assembly.
A few pics may help. This is what the gas block looks like. Also note the new wear on the face of the hammer. And the corresponding new wear on the left side of the carrier. Also I noticed my last time to the range. The first few rounds I belived keyholed, and I had a POI shift. Another thing is when I put an empty mag in and pull the charging handle. It comes out a bit then I've really gotta yank it back. After the hammer is engaged the charging action becomes much easier to pull. And I can smell metal rubbing together alot after multiple charges. :confused:
Is this all new? How many rounds before the gun before this started happening?
Gun ran fine for about 700-800 rounds. Then I stated noticing the ejection pattern change at that time. Last time out to the range, I noticed the key holing and the POI shift. And then my bolt would not lock back. Gun still hasn't had a malfunction other then the bolt not locking on an empty mag.
Buford the pins are still there. Here is a better pic from the bottom of the upper if it helps.
Npena84
In first picture of gas block it appears to be missing the gas tube roll pin. If I'm not mistaken that was what BufordT was referring to. I would try a H2 or H3 buffer if running a carbine buffer or H buffer. I'm using a Colt 9mm buffer in one of mine otherwise I have about the same thing.(suppressed) I was having excess bolt speed cycling to fast for the magazine. My duty rifle is a complete D.D. upper it's over gassed and running with H6 buffer.
Npena84
In first picture of gas block it appears to be missing the gas tube roll pin. If I'm not mistaken that was what BufordT was referring to. I would try a H2 or H3 buffer if running a carbine buffer or H buffer. I'm using a Colt 9mm buffer in one of mine otherwise I have about the same thing.(suppressed) I was having excess bolt speed cycling to fast for the magazine. My duty rifle is a complete D.D. upper it's over gassed and running with H6 buffer.
1- A rifle that's running fine and suddenly starts short stroking isn't doing so because it suddenly becomes over gassed.
2- When an AR is short stroking, it's because the gas has too little energy for the action to function fully with the mass it has. Adding to that mass by changing to a heavier buffer will only make the problem worse. Not every problem an AR has is due to over gassing.
3- A problem cannot be fixed until it's properly diagnosed. The rifle in question was running fine before. Now, it is showing symptoms of short stroking- go to the first post for details. To make the correct diagnosis, the rifle needs to be tested for short stroking without making any changes to the rifle before hand
SonOfAGunn
04-21-15, 20:53
Hey fellas, never really posted. But I've gotten alot of good info off this site. And honestly, I trust the opinions of some on this site better than anyone I could probably find locally.
I have a DDV7 complete upper w/ low profile gas block, mid length gas tube. And a PSA complete lower. That's has a standard spring and a DD H buffer. Anyway the rifle has ran flawless thru 1000 rounds. At about the 700 round mark I noticed the ejection pattern was changing. Because I was picking up alot less brass at the range (almost a foward ejection).
Well last trip to the range the bolt stopped locking on the last round of an empty mag. Cleaned, checked the bolt relubed. Same problem. The mags I used had previously functioned fine. And I was shooting federal xm193. Bolt locks back manually on those same mags. Put oil on the gas key and blew on it, no bubbles. Carrier key isn't loose, extractor and gas rings look fine. Gas tube in the receiver and on the barrel look lined up.
Now there is some new wear on the face of the hammer. And there is corresponding new wear on the bottom of the carrier itself. Now when I was shooting. I used the mag as a monopod. But have read this is ok? I haven't contacted DD yet because think my upper maybe fine. But can anyone tell me what the heck it going on with my gun? Thanks any input would be greatly appreciated ;)
I think that's what you should do personally. Those guys in South GA are top notch. For example, I'm having problems with charging handles that DD did not supply with the rifle. When I called them with my problem, they didn't even ask about ANY details regarding the charging handles. The guy I spoke with, and I can't remember his name, told me to fill out the return info on their website and submit it. I would then be contacted by a rep with a prepaid return label. The rifle would go to his dept. and he'd find out what the problem was. When he figured it out it would get fixed if it was a DD problem, and if it was a charging handle issue then I'd find out for free. He'd then send my rifle back to me. No attitudes just great customer service.
I ended up not sending my rifles to them since the original and other aftermarket (BCM) handles work with no issues whatsoever on my rifles.
Here's a link (https://danieldefense.com/return-merchandise-policy) to the page. You can call them first if you want, I don't think they'd mind.
I don't know how many times I can thank ya'll. I'm heading to the range this am to do some more troubleshooting(pun intended). I would like to go thru as much as I can on end before giving DD a call. I have heard nothing but great things about their CS, so hopefully they can help me out if need be. I'll be sure to post, what I find later. Guess I better stock up on some pistol ammo in the meantime.
After about a thousand rounds it may be time to clean and lube the inside of the magazines, couldn't hurt. Crud in there will slow down the follower.
So I went out to the range yesterday morning. Did the single round test. Bolt still won't lock back. Tried different mags, same deal. Called DD yesterday morning. They will be sending me a return label. Just waiting for warranty to get back to me. Again, I thank everyone for the feedback. I will post the rest of my experience on this space. As well as if I get an answer to what was really going on with my gun.
http://www.brownells.com/userdocs/products/p_100000433_1.jpg
FYI- I was recently contacted after someone else had a DD issue. Turns out the gas port was undersized and that's why it wouldn't run. The stand off of your gas block from the shoulders seems odd, but the block is pinned so it couldn't have moved. I do agree it looks like the roll for the gas tube is missing.
So I went out to the range yesterday morning. Did the single round test. Bolt still won't lock back. Tried different mags, same deal. Called DD yesterday morning. They will be sending me a return label. Just waiting for warranty to get back to me. Again, I thank everyone for the feedback. I will post the rest of my experience on this space. As well as if I get an answer to what was really going on with my gun.
http://www.brownells.com/userdocs/products/p_100000433_1.jpg
Third Rule of the Lazy AR Maintainer- Do not stick anything in the gas tube that you do not want taking permanent residence in there
FYI- I was recently contacted after someone else had a DD issue. Turns out the gas port was undersized and that's why it wouldn't run. The stand off of your gas block from the shoulders seems odd, but the block is pinned so it couldn't have moved. I do agree it looks like the roll for the gas tune is missing.
I think he confirmed the GB roll pin is still there (post #11), just a deceptive picture.
General comments...
If the gun ran fine for 1000 rounds, then begins to short stroke, print keyholes, and has a POI shift at that round count then it's something more uncommon than what causes typical under gassed issues on a fresh build.
Ammo - All of those things point to crap ammo, but he's using XM193. Benefit of the doubt, I guess.
Bore - Mostly for the keyhole/POI shift, but OOS bore can exacerbate short-stroking if the gas port is undersized to begin with. More common with steel cased, but again, XM193 being used. It hasn't been mentioned, but has the OP inspected the bore? It's a known quality barrel, so I doubt he's having bore issues at 1000 rounds, but why not look?
And the most uncommon thing I've ever seen progressively cause those three things, copper fouling built up in the gas port, created by a notably large burr on the muzzle side of the gas port that was big enough to not be shot out. Have you noticed excessive copper fouling on the bolt in the past?
Yeah the pin is still in there. I must be some kind of photographer. I took the pic form about the only angle, that you can see straight thru the hole. StraitR, what should I be looking for in the bore? I haven't noticed any copper fouling out of the ordinary.
Here are some more pics of the bolt carrier, if it helps. They tube on my carrier key looks slightly bent. Idk if that is an issue or not. But overall does that look like a carrier should after 1000 rounds?
Here are some more pics of the bolt carrier, if it helps. They tube on my carrier key looks slightly bent. Idk if that is an issue or not. But overall does that look like a carrier should after 1000 rounds?
The flat area of the gas key around 10-11 o'clock could possibly be problematic. Has it ever been dropped?
Disassemble the BCG and then take just the carrier and slide it into the upper very slowly. See if you can feel it rubbing or binding when the gas key meets the gas tube.
Yeah the pin is still in there. I must be some kind of photographer. I took the pic form about the only angle, that you can see straight thru the hole. StraitR, what should I be looking for in the bore? I haven't noticed any copper fouling out of the ordinary.
I suggest that you thoroughly clean your bore/barrel then inspect from both ends and look for obvious impediments or damage (throat erosion often looks like chips). While a bore issue is highly unlikely, given the manufacturer and round count, anything is possible. There's clearly something out of the ordinary about your problem, because the three issues you're having do not typically occur together on a low round count rifle shooting known good ammo.
Take care to note the condition of the gas port hole, and bore/throat. Pics of recently fired brass could be extremely helpful as well, if you have any.
556BlackRifle
04-25-15, 12:47
The flat area of the gas key around 10-11 o'clock could possibly be problematic. Has it ever been dropped?
Disassemble the BCG and then take just the carrier and slide it into the upper very slowly. See if you can feel it rubbing or binding when the gas key meets the gas tube.
Good eye Steve. I missed that. What do you think about the wear pattern on the 12 O'clock lug?
Good eye Steve. I missed that. What do you think about the wear pattern on the 12 O'clock lug?
Hard to say really. I'm just trying to figure out what has changed in this rifle to suddenly cause it to start having these issues. Given that the gas key should not have a flat spot on it I would suggest starting there.
BufordTJustice
04-26-15, 18:10
Hard to say really. I'm just trying to figure out what has changed in this rifle to suddenly cause it to start having these issues. Given that the gas key should not have a flat spot on it I would suggest starting there.
The recent key holing is a huge red flag for me.
So DD got back to me today. I'm gonna be sending out the upper to them tomorrow morning. They said they think the issue maybe the bolt carrier. Who knows, I'm sure they will figure it out. I will keep everyone posted on the issue. Because I would really love to know what is going on. And maybe find out what happened in the first place. You guys really have been a great help. And I appreciate and am humbled by all your responses. :big_boss:
Marler5811
04-28-15, 19:56
Caroline will make sure you're taken care of. For this type of malfunction, we'll definitely focus on the gas system for starters. This is a classic symptom of short stroking which makes me think there is a gas leak somewhere or not enough is being funneled through the port in the barrel. Our armorers will go through it with a fine toothed comb and repair/replace anything that's found out of whack.
The key-holing very odd for a barrel with such a low round count. do you have a photo of the target that you can email to me?
Caroline was very nice. I know ya'll know what to do. I would love to know what going on. It's just alot of different things that don't add up really. The key holing thing was weird too. I shot 5 rounds to confirm zero. I and was grouping 6 inches high, and the rounds weren't leaving a perfect circle. Put the target back and started shooting again. And to my eye never noticed any more signs of it keyholing again. Save for those first 5 rounds. So I kinda disregard it at first and I threw my target away. Probably should have kept that, and whatever brass I could have. Thanks for reaching out to me Joe.
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