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Posted: 6/7/2010 10:16:50 PM EDT
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Hello All. I've read through the FAQ and performed some of the tests and checks I've read about, so now I'm hoping someone will have ideas for resolving my issues. Here is my setup:
DTI Upper w/ DPMS .204 bbl and all DTI upper parts DTI Lower w/ RRA trigger, all other parts DTI Now here's the problem....Just got back from a prairie dog trip where I fought this stinking thing the entire time. When cycling, it will grab the next round off the magazine regardless of mag brand, but a fair amount of the time it won't go into battery––it will either stop about halfway open, or will appear to go into battery but the carrier isn't quite all the way forward. I started dosing the bolt & carrier wtih RemOil on the trip and that seemed to help a little bit, but the issue is still there. What I've checked....The gas tube appears to be nearly perfectly aligned in the center of the upper and there's no binding on it when the bolt/carrier are pushed closed. The key also appears to be tight and properly staked. Someone suggested taking the upper off, leaving the charging handle seated, pulling the carrier up while holding the upper upright and letting it drop to see if it goes into battery. I did this several times and got the same results. It looks like the bolt is fully seated, but the carrier never quite slides all the way forward. And along those same lines...my brother in law has an ArmaLite AR-10. I noticed that his bolt slides freely in the carrier w/ no resistance. Mine definitely has significant resistance. I've also noticed my buffer has a ring all the way around the outside edge and according to the FAQ section, that shouldn't be happening. Help please! |
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Quoted:
The buffer and spring are the stock parts that came with the DTI kit. Originally this gun was a 20" 5.56 with a collapsible stock. Now it's a 24" .204 with a Choate varmint stock, similar to an A2. Are you running a carbine spring instead of a rifle spring? An A2 stock requires a rifle length spring which is longer. |
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I don't know which length of spring I have––DTI shipped it as a kit for a 20" bbl. I don't know a whole lot about these things but a kit for a 20" should be a rifle length spring, right? Are there standard measurements I could verify?
RE the bolt locking open on the last shot....sometimes. I used a buddy's 20 rd AR Stoner mag and it wouldn't catch with that one. I switched to one of my 30 rounders and that one would catch. Comparing the two mags, it looks like that little plastic lip sticks out just a little more on my mag than my buddy's AR Stoner. At least that's what I attributed that difference in performance to. |
| Taking that last point a step further...I recall that even with an unloaded gun and the action held open, I could push my buddy's AR Stoner mag up into the receiver as far as it would go and the lip on the mag would not engage the bolt release...it just didn't stick out the back of the mag far enough. |
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In another thread, Mort says, "Alignment can sometimes be checked by observing carbon stains on the bottom of the gas block and the top of the barrel near the gas port."
I definitely have carbon stains on the top of the barrel...evident after probably 100 rds or less. So would block misalignment seem to be the most likely problem? |
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Ok ,stroke is normal if the bolt is locking back, so lets move on to why the rifle is jamming on the way forward.
I need you to check the front stop collar edge of the firing pin, the condition of the firing pin retaining pin, and the upper receiver below the barrel feed ramps. I want to confirm that the hammer is not catching the FP collar on the B/C forward stroke, and the rounds are being feed cleanly out of the mag into the feed ramps/chamber, and not being low mag feed with the tips of the bullets striking the upper receiver flat below the lips first before entering the feed lips/chamber. |
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I don't see any signs of abnormal wear in any of those places. If I take the bolt out of the carrier and just work the carrier back and forth in the receiver, I can feel the...gas key? (not sure if that's the right term) rubbing up against the gas tube and I can see a wear ring all the way around the end of the gas tube.
And again, if I let the bolt & carrier drop down into the breech, the bolt will seat but the carrier lacks about 1/8" of being completely closed. I don't think that's completely to blame because when it doesn't cycle, many times the bolt is back far enough to see the mag and the round it's trying to push in. Another thing I've noticed on live rounds pulled back out of the chamber is semi-helical cuts on opposite sides of the bullet. |
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If the round has only it's bullet tip in the barrel extension section, and you can not use the forward assist to walk the B/C any farther forward, bank that the hammer has caught the firing pin collar and locked up the works.
The bolt not fully locking up with a B/C free drop test is normal, and you should be able to set the bolt/get the carrier to touch the front of the barrel extension with a light touch to the back of the carrier. And if none of these are the problem, have you been keeping the upper bearing surfaces well lubed with CLP for break in, and if you are using Hoppes to clean the bore and chamber, have you been flushing such out so there is not remnants/residue of such left in the bore or chamber that could be excelling fouling (plus Hoppes and CLP don't mix well and cause an even worse mess)? Also a chamber brush is your friend, so you one. |
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Quoted:
I was just perusing parts on midway and noticed that rifle and carbine buffers look very different and mine looks like a carbine.  Ordering a rifle buffer and rifle spring right now, hopefully I can try it out this weekend.Full length stock (receiver extension) takes a full length buffer, and standard spring (around 12.5"long), while a shorter telescoping stock takes the shorter carbine buffer and carbine spring (around 10.5" long). If you have been using a carbine spring and carbine buffer in a full fixed butt stock, shotgun the upper open and check the back threaded area of the lower receiver for cracking. As stated, the length of the buffer in the correct receiver extension limits the amount that the B/C can come back, and if you where running such, a cracked lower receiver and loose carrier key is pretty much the norm. If you lucked out with the receiver only be beat to hell and not cracked, I would still pull the key and replace the key bolts. With the correct buffer and spring in the rifle, when pulling back on the charging handle, the face of the bolt should limit out about 1/4" to 3/8" in front of the back of the ejection port. If when pulling back on the charging handle, the face of the bolt retracts way back behind the ejection port, you have the wrong buffer and spring in the rifle. To add, since I don't remember the actual damage to the buffer, but guessing the face has a nice ring in is from when the carrier was stopped via the back of the key to the receiver, and went back a tad further, then was spring sling shot'd back against the carrier again. |
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It's all becoming much clearer. I had a collapsible stock on it and switched to a full length. I don't recall if I ordered a rifle spring, but I'm fairly certain I didn't order a new buffer––it looks exactly like the carbine buffer in the FAQ link. The spring confuses me a bit...I think I read 10.5" for carbine and 12.5" for rifle, but mine measures 11.25"
As for my lower....I can't SEE any cracks, but would they be obvious or something you'd need a magnifying glass to see? I can definitely see where the key is hitting the lower right above the buffer. So what do you say...is the lower safe if I can't see any cracks with the naked eye? And for the key...it's about the same story as the lower. I can see the wear on the back of the key, but there's no play in the key whatsoever. Yes, there is a ring all the way around the edge of the buffer where it's hitting the retaining pin, and that's what I'm really struggling with. My carrier doesn't come into contact with the buffer until you pull it back with the charging handle, so it seems like I'll always have that problem regardless of which buffer I have. Is there something else there that needs to be adjusted??? |
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If the receiver is just dented, should be fine.
Current spring seem like a carbine spring, so order a standard spring with the new standard buffer for the standard receiver extension. Key, don't chance it. Replace the bolts and reinstall the key. Buffer retaining pin chewing the very outer edge of the buffer face, that one should not be happening no mater what buffer was in play (maybe, depending on the amount that the buffer face is U grooved from slamming into the back of the carrier). Something is out of spec since when the upper is closed, the back of the carrier should push the buffer back off the retaining pin. Post a photo of the buffer face since I want to make sure that it's the retaining pin doing the damage, and not just a bur on the back of the carrier (bottom U slot). Also with your bolt locked home, check to confirm that the back of carrier is flush with the back of the upper receiver when open so we can weed that out as well. |
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Already have the spring & buffer on order and getting ready to order the key screws.
Re the damage to the buffer, there is no doubt it is from the retaining pin: The damage is all the way around the outside edge and exactly the height of the retaining pin, plus the retaining pin is shiny where it's coming into contact with the buffer. The back of the carrier is smooth. So let me ask you this then...should the carrier be protruding out the rear of the upper? It seems like that would have to be the case or the carrier would never keep the buffer off the retaining pin. And if the carrier should be protruding out the back of the upper, how do you get it closed? What do you think is out of spec? |
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Back of carrier should be flush with the back of receiver, with the buffer pin retaining the buffer just slightly forward of such math/angle so when the upper comes down, the buffer is pushed back off the retaining pin.
If you want to check the receive to make sure it's in spec (buffer retaining pin channel location), then here, http://www.ar15.com/content/manuals/lowerBlueprint.pdf |
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Quoted:
Already have the spring & buffer on order and getting ready to order the key screws. In your post on 6/8/10, you stated that you changed from a collapsible stock (carbine spring and buffer) to a stock similar to an A2 (needs rifle length spring and rifle buffer) and used the spring and buffer that you had on hand. I asked if you used a carbine spring (and buffer but did not state the buffer) or rifle and never got a reply. My bet is that when you receive the rifle length spring and buffer, you will be good to go. Let us know. |
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Quoted:
Quoted:
Already have the spring & buffer on order and getting ready to order the key screws. In your post on 6/8/10, you stated that you changed from a collapsible stock (carbine spring and buffer) to a stock similar to an A2 (needs rifle length spring and rifle buffer) and used the spring and buffer that you had on hand. I asked if you used a carbine spring (and buffer but did not state the buffer) or rifle and never got a reply. My bet is that when you receive the rifle length spring and buffer, you will be good to go. Let us know. smustian, sorry, thought I replied to your question. I've measured the spring––11.25" uncompressed and the buffer is definitely a carbine buffer. Everything makes a lot more sense now and I think you're right, it should cycle fine once I have the RIGHT parts.  My concern now is that you guys are saying the buffer should not be hitting the retainer pin no matter what and I don't know what to do to fix that. I'm going to check out the link posted above and see if I can make any sense of it.
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New stock, buffer tube, spring, buffer and key screws on their way, should have tomorrow (wanted a new stock & it was cheaper to order it all as a package). Laura @ DTI said my lower isn't under any sort of warranty, so they won't replace it, but she said it sounds like the retainer pin hole may just be at the wrong angle and if that's the case they'll fix that for free. Shipped it on Friday, they should have it Tuesday.
It's probably going to be a little while before I get the lower back and have a chance to put it all together and try it out, but I'm feeling pretty confident my rig will be humming along like a champ now. Thank you all for your input, I really appreciate it! I'll let you know how it turns out. |
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