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Posted: 9/27/2010 4:21:03 PM EDT
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Ok,
So a couple weeks back I got a supposedly Factory LMT Defender 2000 in a trade, it was used, and from all indications it is a factory rifle. Except it seems the previous owner installed a Troy Rail on it. Anyways, I finally get it to the range today, and while im sighting in i realize that the magazine was not seating completely in the rifle. This happened with 2 different 30 rd PMAGs, and 2 Different old beat up Steel mags. This was inserting magazine (completely filled) into the magazine well with the bolt closed. The only way I could get the magazine to catch and hold was if i inserted it while holding the bolt all the way back and then inserting it. Then after firing 1 round the magazine would release again and fall out. it would extract 1 more bullet before falling. So after fiddling with it for awhile i said eff it and i'll worry about it later. I took up my back up rifle and proceeded to have some fun. Then later i was fiddling with it a bit more and realized that loading a magazine with only a few bullets in it would seat properly and fire properly. Then the light primer strikes.. or failure to fires would happen. 1 bullet in 5 would fire, i examined the cartridges and noticed there was a dimple but it was very light and in no way as deep as my back up rifle. At that point i gave up and went back to my other rifle. I was shooting silver bear 62gr. and ive never had a problem with this before. My backup rifle is a DPMS with the only upgrade was a fail-zero BCG, or an LMT m16 BCG (tried them both, no problems) and the dpms ran beautifully like it always does. Ive never had any problems with my AR's before, and they have always ran like tops, so im a bit out of my element here with these malfunctions. I expect this is something stupid and simple, i just really have no clue where to start as i got this rifle in a trade and this was my first time shooting it. someone help please? I plan on taking it apart tommorrow and troubleshooting it but if someone could give me some ideas i can wake up to in the morning it would help alot! thanks! |
Light primer strike, make sure that the hammer spring is installed with the leg winds coming out the bottom, and the legs on top of the trigger pin.
Mag not setting, make sure that the mag catch threads are flush with the face of the button, and when you go to seat a fully loaded mag, use the palm of your hand to slap drive it on the last of the way. The rounds have to compress in the mag to allow the mag to fully seat, and if the spring or mags are still new, it may take some time until you will be able to seat them alone by hand (just pushing up) with the B/C locked home. |
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Ok, so i think i have the mag catch problem fixed, as much as i can figure it out without actually test firing, i loosened it up by 1 turn and it appears to be working correctly now.
the light strikes im still a bit stumped, the trigger appears to be correct to me? (horrible lighting in picture and focus, but the spring legs ARE on the top of the trigger) 
only other thing i can notice that looks funky is it appears that the reciever extension tube is 1 turn too loose? the dentent is sitting right on the top edge of the curl in the end of the tube, it appears that it should be tightened down by 1 turn. 
also the buffer seems awful chewed up for the supposed round count, but possibly its just because of the black coating on it that i notice the wear... the black coating denotes a heavy buffer correct? 
does lmt put in heavy buffers in the defender 2000 series stock? Would either of these issues (reciever extension not fully tightened, chewed up buffer) be causing these light strikes? thanks alot for your time and patience! |
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The one thing that I am seeing is that you are running the rifle way too dry for coated ammo.
Without having the rifle in hand to check items like firing pin protrusion and such, what I would suggest is to run the rifle more wet on the CLP side for break in. Also with coated ammo, you have scrub out such fouling since normal copper solvents will not dissolve it. For this, a chamber brush is a must for cleaning the chamber. So before your next outing, spray CLP both inside and out on the B/C, give it a flick to knock off the excess, then run the rifle that wet for coated ammo/break in. As of now, would dare to guess that the Bolt was not fully locking home, with the back of the carrier blocking the FP from reaching full protrusion and the reason for the light strikes. |
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That makes no sense, i gave the rifle a oil coating AND was running my fail-zero BCG in it. which is the same thing i run in my DPMS completely dry, and that feeds perfectly.
idk, i guess ill just tighten up the buffer tube and take it back out this weekend and see what happens. |
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Quoted:
That makes no sense, i gave the rifle a oil coating AND was running my fail-zero BCG in it. which is the same thing i run in my DPMS completely dry, and that feeds perfectly. idk, i guess ill just tighten up the buffer tube and take it back out this weekend and see what happens. Sounds like someone didn't want to fool with this rifle and found a lucky buyer to continue the trouble shooting. Each rifle manufacturer does things a wee bit different, as they don't have the full TDP Colt uses. Even rifles made by the same maker may have slight differences that add up when the parts are fitted together. Colt rifles even have troubles from time to time :) Dano523 is giving you some very well reasoned information that applies to the AR15 system. The bolt and its relationship to the barrel extension can need a break-in period so the parts completely marry to eachother. Sometimes this aint like putting things together like Legos. I would check the firing pin, see if it is slightly short, by measuring how far it protrudes from the bolt face. Maybe swap in another firing pin. Run the bolt group wet and scrub the chamber very well to get at the residue that gets into the chamber. Maybe even try a different brand of ammunition, as some rifles run better when fed the brand it likes. "Would either of these issues (reciever extension not fully tightened, chewed up buffer) be causing these light strikes?" The rear face of your bolt carrier is slightly sharp in spots and causing it to chew up the buffer. Lightly stone the edges of the bolt carrier, especially the area that rides over the buffer retainer, to ease the edges and knock down any sharp spots. Give this buffer a good run before replacing it, it looks like it has good life left. Let us know how it works out. |
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Are the light primer strikes before or after pulling the trigger?
If it's before, then there is no problem. The free floating firing pin lightly hits the primer as the bolt closes on the loaded chamber. If it's after pulling the trigger, then you have a weak hammer spring. The scratches on the buffer... well take a real fine stone and LIGHTLY stone off the slight burr that is at the end, on the chanel, that the buffer retainer rides through on the underside of the bcg. |
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yeah, while i was at the range i swapped out the BCG's from my back up to this one, and still was doing it.
then i swapped the firing pins. no dice. firing pins looked the same. i am not a complete noob with AR's. i built my backup rifle and its perfect. never had so much as a hiccup. i just assumed this new one was GTG because it didnt have any glaring obvious faults and it is supposedly a factory LMT. ooooh... you know what.... huh... i was just thinking... it appears that the previous owner installed a troy rail system. I dont think those come from LMT that way. and it is slightly canted off to the side, which leads me to believe it was an amatuer install. is it possibly they mucked up the gas tube while installing the rail system? possibly don't have the correct space off the shoulder of the barrel on the gas block? would something like that cause failure to fire? |
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Quoted:
Are the light primer strikes before or after pulling the trigger? If it's before, then there is no problem. The free floating firing pin lightly hits the primer as the bolt closes on the loaded chamber. If it's after pulling the trigger, then you have a weak hammer spring. The scratches on the buffer... well take a real fine stone and LIGHTLY stone off the slight burr that is at the end, on the chanel, that the buffer retainer rides through on the underside of the bcg. can you explain this sanding your speaking off in more detail... i dont quite grasp what your saying to sand. as far as the light primer strikes... this is what happens... 1. insert magazine 2. rack charging handle 3. fire off a round (or failure to fire) 4. round either extracts correctly or i rack the charging handle ejecting the failed to fire round. (examine round, has a light dimple) 5. pull trigger... failure to fire.... (extract round, examine round, has light dimple) the failure to fires are defintly after i pull the trigger. |
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Pictures and step by step here:
http://www.weaponevolution.com/forum/showthread.php?1744-BOLT-CARRIER-LAPPING-DEBURRING-PROCEDURE |
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i think this post got lost in the shuffle so ill repost it.
yeah, while i was at the range i swapped out the BCG's from my back up to this one, and still was doing it. then i swapped the firing pins. no dice. firing pins looked the same. i am not a complete noob with AR's. i built my backup rifle and its perfect. never had so much as a hiccup. i just assumed this new one was GTG because it didnt have any glaring obvious faults and it is supposedly a factory LMT. ooooh... you know what.... huh... i was just thinking... it appears that the previous owner installed a troy rail system. I dont think those come from LMT that way. and it is slightly canted off to the side, which leads me to believe it was an amatuer install. is it possibly they mucked up the gas tube while installing the rail system? possibly don't have the correct space off the shoulder of the barrel on the gas block? would something like that cause failure to fire? |
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minor update.
broke the guns down and cleaned. Jeez, my back-up was dirty. the LMT seems to be ok, although upon close inspection it appears that the gas tube was slightly bent. I could just about kick that guy who sold me this. seriously. Straightened out the tube as much as i could, ir appears to be seating in the key correctly. but it really wasnt bent enough to where it wasnt seating properly before. eh idk? function checks out fine. mags are seating properly. I guess this will be all the story until i get it back out to the range this weekend. if anyone has any other ideas of things to try feel free, ill check this thread every once and awhile. |
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Quoted:
minor update. broke the guns down and cleaned. Jeez, my back-up was dirty. the LMT seems to be ok, although upon close inspection it appears that the gas tube was slightly bent. I could just about kick that guy who sold me this. seriously. Straightened out the tube as much as i could, ir appears to be seating in the key correctly. but it really wasnt bent enough to where it wasnt seating properly before. eh idk? function checks out fine. mags are seating properly. I guess this will be all the story until i get it back out to the range this weekend. if anyone has any other ideas of things to try feel free, ill check this thread every once and awhile. I'm not really sure what you are talking about. Light primer strikes? or failure to feed? If you are hitting primers on brownbear with an old dpms spring they may not ignite. I was under the impression you were having light primer strikes, thus the gun not firing. So it fires, but doesn't cycle? Is that why you are checking the gas tube? Now I'm cornfused 
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Quoted:
Quoted:
minor update. broke the guns down and cleaned. Jeez, my back-up was dirty. the LMT seems to be ok, although upon close inspection it appears that the gas tube was slightly bent. I could just about kick that guy who sold me this. seriously. Straightened out the tube as much as i could, ir appears to be seating in the key correctly. but it really wasnt bent enough to where it wasnt seating properly before. eh idk? function checks out fine. mags are seating properly. I guess this will be all the story until i get it back out to the range this weekend. if anyone has any other ideas of things to try feel free, ill check this thread every once and awhile. I'm not really sure what you are talking about. Light primer strikes? or failure to feed? If you are hitting primers on brownbear with an old dpms spring they may not ignite. I was under the impression you were having light primer strikes, thus the gun not firing. So it fires, but doesn't cycle? Is that why you are checking the gas tube? Now I'm cornfused
First, im using silver bear.. not brown bear. not sure if there is a difference in the primers but yea. im having failures to fire. or light primer strikes... 1 out of 5 rounds will successfully fire. the other 4 rounds will click but no bang. light indentation on the failure to fire rounds. when it does fire.. it cycles correctly, no problems. this is on a factory LMT rifle, that i recieved in trade. the only non factory parts on the rifle that i can see is the 9 inch troy rail system. I believe the previous owner put that on, and im wondering if possibly he mucked up the gastube/block during assembly. the DPMS is my backup rifle, i built it and it has always fired perfectly and contuines to do so. No problems running the exact same ammo, from the exact same lot, at the exact same time this was all happening. i tried to switch my uppers, but i was having magazine issues and magpul BAD lever compatibility issues between the 2 uppers and no tools to take it off. I will be switching out uppers next if i contuine to have problems after i get to the range this weekend. |
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Quoted:
Quoted:
Quoted:
minor update. broke the guns down and cleaned. Jeez, my back-up was dirty. the LMT seems to be ok, although upon close inspection it appears that the gas tube was slightly bent. I could just about kick that guy who sold me this. seriously. Straightened out the tube as much as i could, ir appears to be seating in the key correctly. but it really wasnt bent enough to where it wasnt seating properly before. eh idk? function checks out fine. mags are seating properly. I guess this will be all the story until i get it back out to the range this weekend. if anyone has any other ideas of things to try feel free, ill check this thread every once and awhile. I'm not really sure what you are talking about. Light primer strikes? or failure to feed? If you are hitting primers on brownbear with an old dpms spring they may not ignite. I was under the impression you were having light primer strikes, thus the gun not firing. So it fires, but doesn't cycle? Is that why you are checking the gas tube? Now I'm cornfused
First, im using silver bear.. not brown bear. not sure if there is a difference in the primers but yea. im having failures to fire. or light primer strikes... 1 out of 5 rounds will successfully fire. the other 4 rounds will click but no bang. light indentation on the failure to fire rounds. when it does fire.. it cycles correctly, no problems. this is on a factory LMT rifle, that i recieved in trade. the only non factory parts on the rifle that i can see is the 9 inch troy rail system. I believe the previous owner put that on, and im wondering if possibly he mucked up the gastube/block during assembly. the DPMS is my backup rifle, i built it and it has always fired perfectly and contuines to do so. No problems running the exact same ammo, from the exact same lot, at the exact same time this was all happening. i tried to switch my uppers, but i was having magazine issues and magpul BAD lever compatibility issues between the 2 uppers and no tools to take it off. I will be switching out uppers next if i contuine to have problems after i get to the range this weekend. I had the same problem with my 5.45x39 ar. The primers were too tough for the rra spring, so I put a heavy spring in it, and it doesn't light strike anymore. Good luck man, I'd say try another upper and if it light strikes, replace the hammer spring. |
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