View Full Version : Buffer Retaining Pin....Is this ok??
I can not make another turn without hitting the pin....is this going to hold up?? thanks
http://i1117.photobucket.com/albums/k585/tropics1977/DSC06594.jpg
http://i1117.photobucket.com/albums/k585/tropics1977/DSC06592.jpg
http://i1117.photobucket.com/albums/k585/tropics1977/DSC06593.jpg
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Boy! Looks like it is barely caught but it will probably be fine. I'd keep my eye on it but it is a low stressed part that is only used when you open the gun.
Just curious, what make Buffer Tube and Lower are you using?
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As long as that pin can't jump out (which obviously it has not) I think you're fine.
:D
As in you should be glad that it just barely made it!
:D
It is a Bcm tube and a cmmg lower....I have another one with the same setup but it covers alot more of the pin.....I have not used this lower much.....i grabbed the pin with some pliers and tried to pull it out and i dont think its going to come out, but i wanted to get some other opinions
It is a Bcm tube and a cmmg lower....I have another one with the same setup but it covers alot more of the pin.....I have not used this lower much.....i grabbed the pin with some pliers and tried to pull it out and i dont think its going to come out, but i wanted to get some other opinions
Yeah I built one like that once. That little pin is under some pressure. If it could come out physically it would have already.
If you are mangling your pin enough to make it deformed enough to come out of that hole then you got bigger issues than the buffer tube my friend.
And just some advice (I'm not as high speed as most around here but I try) do a good job staking that castle nut in 2 places to keep the tube from turning.
:p
KrampusArms
04-19-12, 23:40
OP. THAT is exactly how much my pin is retained as well. I also have a CMMG lower, with the same brand Milspec extension. Your timing is perfect as I was searching for threads on this exact issue. I also was concerned about my pin popping out, & as we know that would equal a horrific stoppage.
I have a question for the forum brain. Could this be an indication of the me & the OPs lower being out of spec?
SpankMonkey
04-20-12, 00:20
OP. THAT is exactly how much my pin is retained as well. I also have a CMMG lower, with the same brand Milspec extension. Your timing is perfect as I was searching for threads on this exact issue. I also was concerned about my pin popping out, & as we know that would equal a horrific stoppage.
I have a question for the forum brain. Could this be an indication of the me & the OPs lower being out of spec?
Yes.. The tube or the lower. My money would be on the lower.
If truly paranoid about it (which no one seems to be) you can take a round jewelers file and notch the lip of the RE to allow that one more turn and more coverage of the retaining pin.
Downside is that the top of the RE may protrude too far out of the 'collar' on the forward side which can interfere with upper to lower fit.
If it does, that too can be dressed off with a standard half round file after marking where things need to go away.
Just a matter of several test fits before locking everything down.
Without seeing it in person, I find that to be unsat. I would not be comfortable with that little purchase on the pin. If you try that RE in another lower, what do you get? If you try another RE in that lower, what do you get?
Eurodriver
04-20-12, 06:18
Without seeing it in person, I find that to be unsat. I would not be comfortable with that little purchase on the pin. If you try that RE in another lower, what do you get? If you try another RE in that lower, what do you get?
Blah blah blah, here I am agreeing with Rob again.
My RE almost butts up to the "tit" itself. I would be worried with hard use, that would possibly shimmy itself loose.
I would not feel comfortable with the retaining pin as is. I would do as GT said and file a little of the buffer tube until there is more contact with the pin. I have had to repair several rifles when the pin came loose. Thankfully it was in training. Believe me it's a pain in the ass to get them out.
Ok....I have a different Bcm Extension that i put in the lower.....it works alot better.....but i put the newer tube that was in it in a noveske lower and it worked fine also..........i have a friend who owns a machine shop and i am going to get him to turn a little off the new one......it doesnt need much as i can make another full turn but it butts up to the tit
Ok....to Krampus....I hit my tube with a bastard file and made another turn....it was very easy to do and took all of 2 minutes....and i KNOW it isnt coming out now.
EHilderbrand
04-20-12, 11:34
I've had similar concerns. Glad to also see this topic as I have ran in to this with several different brands, actually.
This is after fililing it a little and going another turn....
http://i1117.photobucket.com/albums/k585/tropics1977/DSC06604.jpg
http://i1117.photobucket.com/albums/k585/tropics1977/DSC06602.jpg
Whatever you do, don't do this:
http://i210.photobucket.com/albums/bb201/trixiebud/grind.jpg?t=1300216557
KrampusArms
04-20-12, 14:14
Tropics that is much better. Wow. Im going to have to get a castle nut wrench so I can do the same.
Ash, WTF happened there?! Did the guy sawzaw the whole thing???
Tropics that is much better. Wow. Im going to have to get a castle nut wrench so I can do the same.
Ash, WTF happened there?! Did the guy sawzaw the whole thing???
I was going to take it to a friends machine shop but i had a file handy and decided to try it and i was surprised how fast and easy the file shaved it down......on a side note i was scared that the upper part of the tube would protrude out past the lower and prevent the upper from closing.....but on mine it didnt.
If it did, the same file would have reconciled the issue.
Tropics that is much better. Wow. Im going to have to get a castle nut wrench so I can do the same.
Ash, WTF happened there?! Did the guy sawzaw the whole thing???
Some tard on TOS didn't understand that the RE is supposed to retain the pin via compression so he filed a notch into it and then realized it was too long for the upper to close so he filed the excess material off the end.:suicide2:
EDIT: markm made this thread about it here last year. This incident reminded me of it: https://www.m4carbine.net/showthread.php?t=76598
That's the correct fix and also pretty funny in the face of the folks who freak out over Dremel'd feed ramps. :D
KrampusArms
04-20-12, 20:34
That was a job gone horribly wrong. Thanks for the link.
My particular extension required the slightest circular notch. It took a few delicate swipes with the file. It turned one more revolution, & now theres no way in hell this retainer is popping out.
Is there any chance of the buffer slamming into the retainer on the return cycle? How far is the buffer compressed into the extension when the upper is closed?
you should feel the back of the carrier push off of the buffer when you pin the receivers back together.
This seems to happen from time to time.
That bottom lip is supposed to protrude something like .060"
I had the exact same issue with a RE from another excellent mfg.
After i verifed proper fit with another RE, the MFG sent a new one out and I returned the defective unit in the same box.
Units with minimal engagement should be returned.
I was concerned that filing some off and going another turn would make the tube shorter and the bolt might not lock after the last round or it might not cycle properly.
KrampusArms
04-20-12, 22:54
I was concerned that filing some off and going another turn would make the tube shorter and the bolt might not lock after the last round or it might not cycle properly.
I sure hope not.
good on the left, crap on the right.
http://i13.photobucket.com/albums/a264/artweaker/Troubleshooting/ColtOAILREfront.jpg
http://i13.photobucket.com/albums/a264/artweaker/Troubleshooting/ColtLREtiminglip.jpg
Got calipers?
Simple fix, just remove castle nut (this can be done with channel locks and some sort of leather / towel so you do not mar it) screw the tube in one rotation and your gtg. I wouldn't continue use as is though.
I just had an SW MP-15 come through with the same issue. The buffer retaining pin was held only with a hair and a hope of contact with the RE. Another full revolution of the RE and the pin dragged. I hit it with a file to give it some clearance it is GTG.
DPMSTacticool
04-29-12, 14:04
I had a buffer tube much like yours that barley sat on the retaining pin. After about 200 rounds the little bit of buffer holding the pin down broke and the pin lodged itself in the bolt carrier and I had a hell of a time getting it out. If you depress the pin fully and then rotate the buffer tube one more time you should be fine, if not I suggest filing a little off of the buffer tube until you can twist it enough to hold the pin more securely.
Hope this helps.
Suwannee Tim
04-29-12, 14:45
......After about 200 rounds the little bit of buffer holding the pin down broke and the pin lodged itself in the bolt carrier and I had a hell of a time getting it out.........
This part is "unimportant", the rifle will work just fine without it but you certainly don't want loose parts rattling around in the works.
This is completely off topic but can I get you DPMS to expound on your choice of user name?
DPMSTacticool
04-29-12, 18:43
This is completely off topic but can I get you DPMS to expound on your choice of user name?[/QUOTE]
Haha I figured everyone on this website hates two things DPMS and Tacticool mall ninjas, so in my limited knowledge decided to put two negatives together in hopes it would create a positive.:ph34r:
KrampusArms
04-29-12, 18:49
Is there any issue to turning the tube one more revolution? Could this produce short stroking symptoms? What is the minimal clearance necessary between the bolt & bolt stop?
What I'm trying to say is can the receiver extension be threaded to far in, that it would mess up your cycling/hold open?
Suwannee Tim
04-29-12, 19:10
....two negatives together in hopes it would create a positive....
Very clever.:D
Back to the buffer tube, you could just trim the length as needed. Ideally you would use a lathe but if none is available you could use a belt sander or a file. A big file will do the trick, you need to hold the extension rigidly and firmly as in a vise so you can lean into the file. One of the requirements of taking off quantities of metal with a file is you need to lean into it with some force and give smooth, forceful strokes.
Usually not. Like others, I've had to file an RE before. With your bolt locked back, keep pressure on the bolt catch and, while looking inside the ejection port, see how much further you can pull the bolt back. About 1/4" is normal, I wouldn't want anything less than probably an 1/8".
Is there any issue to turning the tube one more revolution? Could this produce short stroking symptoms? What is the minimal clearance necessary between the bolt & bolt stop?
What I'm trying to say is can the receiver extension be threaded to far in, that it would mess up your cycling/hold open?
Very clever.:D
Back to the buffer tube, you could just trim the length as needed. Ideally you would use a lathe but if none is available you could use a belt sander or a file. A big file will do the trick, you need to hold the extension rigidly and firmly as in a vise so you can lean into the file. One of the requirements of taking off quantities of metal with a file is you need to lean into it with some force and give smooth, forceful strokes.
Or you could simply file a NOTCH like was originally suggested. :)
Or you could just install an LMT RE that takes the guesswork out of it for you. Screw it in until the built in notch engages retaining pin. No guesswork required.
Suwannee Tim
04-30-12, 15:28
Or you could simply file a NOTCH like was originally suggested. :)
I thought the consensus was the notch was bad form. I ain't too proud to save a little work.
Thinking on it a little more and considering Murphy's Law, just as soon as you file a notch you or someone else will try to remove the RE forgetting or not knowing about the notch and booger up the RE, pin and maybe even the lower. Better to trim the entire RE than file a notch.
I couldn't imagine why, the end result is the same either way. I am not sure I would be so quick to call any lower or RE defective if this problem were to present itself. I would attribute it to tolerance stacking.
I can't imagine that the thread roller or tap is engaging every RE and every lower at the same place every time on every piece at every manufacturer. So there are going to be some differences in where the threads start which will result in slight differences and once in a blue moon, a problem like this.
If this level of quality control like this existed in firearms, screws would be tightened by the number of turns and not torque.
I think you'll be okay with it. Just check it out frequently after you fire.
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