Help...FTFeed and double feed
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Old 04-09-2011, 10:22 PM   #1
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Default Help...FTFeed and double feed

Today I shot in a local match, and while I shot well my rifle did not cooperate. The rifle is a DPMS Sweet sixteen with bull barrel and M4 feed ramp. Shooting 55 grain PMC Bronze. I have had the rifle almost 2 years and it has about 700 rounds down range. When I first got the rifle it had a slight problem feeding but I thought it was a mag problem b/c it went away when I started using PMAGS. Today it failed to load about 25 times. I shot about 80-100 rounds today, but the rifle was broken down last night and cleaned and lubed to death, with REM Oil. I even sprayed it down during the lunch break after my first FTF episod( i say episod b/c it failed on 6 of 15 shots, and double fed twice). On the next stage it failed to feed twice. So for the last stage I borrowed a G.I. mag from a friend to rule out the mag as the issue and yet again it failed which is shown in the video(at least I shot the stage clean). As you can see by the end of the day it was doing it almost every time My only thoughts are that this has to be some type of gas issue, but my knowledge of the AR doesn't extend much beyond my capabilites to break it down, clean and lube. I've got a month before the next match and I've got to get this issue resolved or I might just lose it.

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Old 04-09-2011, 11:01 PM   #2
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I didn't watch the video, I am on an aircard and it takes forever to download.

But it sounds like it is short stroking, on you. Which could be a sign of not enough gas pressure getting through your return tube, or that your Buffer spring is too stiff (which could also be a problem of your buffer itself being "too heavy" for the resulting gas pressure).

How many rounds do you have through the upper in question? And have you ever taken a pipe cleaner to your gas tube to clean it out?

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Old 04-09-2011, 11:09 PM   #3
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Originally Posted by Dillinger View Post
I didn't watch the video, I am on an aircard and it takes forever to download.

But it sounds like it is short stroking, on you. Which could be a sign of not enough gas pressure getting through your return tube, or that your Buffer spring is too stiff (which could also be a problem of your buffer itself being "too heavy" for the resulting gas pressure).

How many rounds do you have through the upper in question? And have you ever taken a pipe cleaner to your gas tube to clean it out?
I have about 700 rounds down range, and no I have not taken a pipe cleaner into the gas tube, but you can bet your ass i'll have one before the night is done. Since I have never done that,(dont know why i haven't even thought to do that) is there anything I should look out for when I cleaning it.
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Old 04-09-2011, 11:18 PM   #4
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JWHIRL,

Yes sir you certainly have some issues. Obviously it is very hard to diagnose problems over the web. But one thing I would advise not being prejudiced. But Rem Oil is not a good lube for the AR Rifle System. It is too light in consistency. There are many good products for the AR Rifle. Some being Breakfree (Be sure to shake before using!) G-96 which Rock River Arms uses exclusively for lubricant other than Hoppes Solvent for cleaning. The Mobile #1 Synthetic formula mentioned here on the forum and many other good lubes. But not Rem Oil!
Anyway you could have a definite gas problem from what I saw. A couple of suggestions and please feel free to PM me if you like. Of course if we do find what it is we will share it with the other members of the forum for educational purposes. So without getting into too long of reply here lets get started.

First lets not presume the barrowed mag was flawless.

#1. Get some good Lube for the rifle, bolt and carrier. The Bolt and Carrier Group specifically should look a little wet when lubed.
#2. Disassemble your Bolt and Carrier Group for cleaning. Be sure the carbon is removed from the tail shaft of the Bolt.
#3. Check the gas rings for wear, roll over or damage by visual and feel.
#4. After your Bolt and Carrier Group has been cleaned and reassembled.
Pull your Bolt "Out" to it's full extended position in the Carrier. Like it would need to be if you were going to assemble it in the receiver.
Now, set the Bolt and Carrier in the vertical position upright with the Bolt Face setting upright on a flat surface. If the weight of the Bolt Carrier alone causes the Carrier to fall down and close on the Bolt. Replace your gas rings. This is the Armorers test! And could cause your problem. Please PM me to discuss this more in detail if you choose. I will be glad to give you my TX if you would rather talk in person about it.

03

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Old 04-10-2011, 02:29 PM   #5
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Wow that sucks huh.. Did you buy it nib? If it has done it since new I wonder if you have an assembly issue like the gas port and gas block/sight not correctly aligned ?

I have an older BM upper I got second hand and has a similar problem, It has some errosion on the front sight where the tube goes in and allows gas to leak by. I noticed it when I pulled the hand guards off and can see the black carbon stains where the gas is escaping.

I hope you get it resolved, I snap if I had one with a 25% failure rate

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Old 04-10-2011, 02:47 PM   #6
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I have about 700 rounds down range, and no I have not taken a pipe cleaner into the gas tube, but you can bet your ass i'll have one before the night is done. Since I have never done that,(dont know why i haven't even thought to do that) is there anything I should look out for when I cleaning it.
700 rounds is definitely not enough to have clogged the gas tube to the point of failure. If you had 1700, that might be something to check.

Basically clean with the pipe cleaner and see how grimy/gritty it is, repeat until the pipe cleaner comes back the same color.

I am leaning towards the weight of your buffer and/or the buffer spring, unless you have an initial assembly issue as stated above.

Check your BCG group as instructed by sniper above, but I am going to be surprised if your rings are shot already after 700 rounds.

Do you have a buddy with an AR that you can try your upper on his lower and see if the samehing happens??
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Old 04-10-2011, 03:28 PM   #7
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im in agreement with sniper.

rem oil is little better than sewing machine 3in1 oil or wd40. its more fit for use as a light machine oil on bicycle chains and fishing reels. rem oil shouldnt be used on firearms in my opinion.

compound that with possibly slightly worn or out of spec gas rings with the extra friction from improper lube and you got FTF.

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Old 04-11-2011, 01:38 AM   #8
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Quote:
Originally Posted by Dillinger View Post
700 rounds is definitely not enough to have clogged the gas tube to the point of failure. If you had 1700, that might be something to check.

Basically clean with the pipe cleaner and see how grimy/gritty it is, repeat until the pipe cleaner comes back the same color.

I am leaning towards the weight of your buffer and/or the buffer spring, unless you have an initial assembly issue as stated above.

Check your BCG group as instructed by sniper above, but I am going to be surprised if your rings are shot already after 700 rounds.

Do you have a buddy with an AR that you can try your upper on his lower and see if the samehing happens??
JD, if it is indeed a buffer weight or spring problem, do you think the buffer is too heavy or too light.
I cleaned the gas tube today, and it was pretty clean so that probably isn't the issue I was hoping it was that simple). I am going to take it out tomorrow and see if the new lube is any better. I am also going to try to get a lower from a friend to see if it runs any better.
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Old 04-11-2011, 01:56 AM   #9
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Quote:
Originally Posted by jwhirl413 View Post
JD, if it is indeed a buffer weight or spring problem, do you think the buffer is too heavy or too light.
I cleaned the gas tube today, and it was pretty clean so that probably isn't the issue I was hoping it was that simple). I am going to take it out tomorrow and see if the new lube is any better. I am also going to try to get a lower from a friend to see if it runs any better.
My initial "over the interwebz, off the top of my head" thought is that your buffer may be too heavy. The gas pressure isn't high enough to compress the spring fully to get the BCG well behind the round with the force to feed out of the mag.

Since you tried different mags, and you have the more lowered, more flared M4 feed ramps, I have to think that when your BCG comes back, it's not coming back with the umph needed.

The sweet sixteen has the mid length gas recovery system, of which I am not personally a fan, but that is just me. In theory a shorter return path for gas harnessed closer to the initial explosion of the round in a confined space should lead to BETTER chances for full cycling. But we have seen alot of problems with both accuracy and cycling with the mid length models, but I can't honestly tell you the last time I worked on a DPMS.

They are usually pretty darn good.

I am curious to see what your upper would do on a different lower. One that has a different stock configuration, and presumably, a different weight buffer and spring.

Please keep us informed as I am most curious.

JD
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Old 04-11-2011, 01:53 PM   #10
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Default think i figured it out...i'm an idiot

Well I guess this makes me feel better about the gun, and while not 100% because I haven't tested it, I'm pretty sure I have found the problem. I did not realize that I needed a smaller buffer with a collapsible stock, and JD talking about the buffer and spring got me thinking about it. While I feel like a moron, I'll be changing the stock back out, take it to the range to see how it works, and if all goes right, i'll re-install the collapsible stock when the new buffer gets here. Feel free to point and snicker. I am.

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