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Bolt stop not locking at the end of the mag


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#1 Carny

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Posted 12 July 2012 - 08:11 AM

As the title says, I've had some issues with the bolt stop not engaging properly at the end of the mag.  Anybody got any ideas?

Checked all the mags.  All the tabs are in the right place.  Have around 1k rounds through the rifle.  Tested at 80 degrees (roundabout) with GG.

#2 TheBios42

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Posted 12 July 2012 - 08:47 AM

Have you opened the receivers to look at the bolt catch to see any ware?

#3 aaps59

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Posted 12 July 2012 - 09:11 AM

Does this happen on semi as well? I have experienced this with some of my mags as well, but I figured it was just because of mag cool down after a full auto mag dump. It led me to fire at opposing teams without me knowing there was nothing coming out haha

#4 akiraspeedstar

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Posted 12 July 2012 - 11:40 AM

The bolt catch operates similar to my old Tokyo Marui SOPMOD, the bb follower hits a lever, which hits another lever, which then hits a lever in the lower receiver.

so itd either be the mags levers being caught up by debris or possibly something in the bolt catch on the receiver. If its not debris then itd probably be some damage/wear to the bolt catch system.

#5 greatwatermelon

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Posted 12 July 2012 - 12:48 PM

Oil could be making the bolt catch a lil' sticky.

#6 BoobieM4H

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Posted 12 July 2012 - 01:09 PM

Your bolt is probably worn out where the bolt catch engages..check to see if its rounded corner on bolt..if it is its due to the bolt catch not moving far enough up to engage the bolt. The bolt catch catches about 2mm on the bolt face..which is not a lot of material..

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#7 kullwarrior

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Posted 12 July 2012 - 02:12 PM

 akiraspeedstar, on 12 July 2012 - 11:40 AM, said:

The bolt catch operates similar to my old Tokyo Marui SOPMOD, the bb follower hits a lever, which hits another lever, which then hits a lever in the lower receiver.

so itd either be the mags levers being caught up by debris or possibly something in the bolt catch on the receiver. If its not debris then itd probably be some damage/wear to the bolt catch system.

ERRR WRONG.
BB follower hits a lever -> Lever on magazine raised -> Hits bolt catch -> Bolt catch raised -> hits bolt carrier -> cause bolt carrier to lock back

Essentially this is how every GBBR operates....AR-15 is the same except the follower hits the bolt catch directly.

 TheBios42, on 12 July 2012 - 08:47 AM, said:

Have you opened the receivers to look at the bolt catch to see any ware?

No that won't be the case, WRONG! (I actually had the same issue, bolt catch has stronger steel than bolt carrier FYI)

 BoobieM4H, on 12 July 2012 - 01:09 PM, said:

Your bolt is probably worn out where the bolt catch engages..check to see if its rounded corner on bolt..if it is its due to the bolt catch not moving far enough up to engage the bolt. The bolt catch catches about 2mm on the bolt face..which is not a lot of material..

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#8 niko_gpsy

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Posted 12 July 2012 - 02:33 PM

I would agree that the section on the front of the bolt that the bolt catch engages may have been worn out.

#9 akiraspeedstar

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Posted 12 July 2012 - 02:46 PM

Ill take a look at it again, but from what Ive seen the mags lever hits a lever in the lower receiver which then raises the bolt catch. So I forgot to mention the bolt catch, also I swear I saw two levers in the magazine, one activating the other.

Considering that he doesnt have many BBs through his gun I didnt expect the bolt catch or bolt to be worn yet to that point.

#10 BoobieM4H

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Posted 12 July 2012 - 02:50 PM

 akiraspeedstar, on 12 July 2012 - 02:46 PM, said:

Ill take a look at it again, but from what Ive seen the mags lever hits a lever in the lower receiver which then raises the bolt catch. So I forgot to mention the bolt catch, also I swear I saw two levers in the magazine, one activating the other.

Considering that he doesnt have many BBs through his gun I didnt expect the bolt catch or bolt to be worn yet to that point.
Bolt catch has a little arm that extends from it that is pushed up from one of the cam levers inside the mag

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#11 R_King91303

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Posted 12 July 2012 - 03:51 PM

 akiraspeedstar, on 12 July 2012 - 02:46 PM, said:

Ill take a look at it again, but from what Ive seen the mags lever hits a lever in the lower receiver which then raises the bolt catch. So I forgot to mention the bolt catch, also I swear I saw two levers in the magazine, one activating the other.

Considering that he doesnt have many BBs through his gun I didnt expect the bolt catch or bolt to be worn yet to that point.

There are two "arms" in the magazine. When the BB follower comes into contact with the first arm, it pushes its "hand" down onto the second arm. This second arm then pushes its hand up and engages something to stop the bolt. By removing the second arm, you will disable the bolt stop function so you don't have to hold on to the bolt release to dry fire.


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#12 BoobieM4H

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Posted 12 July 2012 - 04:06 PM

 R_King91303, on 12 July 2012 - 03:51 PM, said:


There are two "arms" in the magazine. When the BB follower comes into contact with the first arm, it pushes its "hand" down onto the second arm. This second arm then pushes its hand up and engages something to stop the bolt. By removing the second arm, you will disable the bolt stop function so you don't have to hold on to the bolt release to dry fire.


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Any lever inside the mag can be removed to disable bolt catch function. If I were to want to disable it I would remove the lever that is moved by the bb follower..and leave the lever that pushes up on bolt catch in..removing the lever that pushes the bolt catch would leave a gap (hole) there and would be an ideal place for debris to go into.

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#13 BoobieM4H

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Posted 12 July 2012 - 04:08 PM

So not to confuse folks my "levers" are the same as R_kings "arms" :)

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#14 Carny

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Posted 12 July 2012 - 07:40 PM

Fixed it, I think.  Agreed, there's not a lot of material there to catch the bolt.  

The bolt catch was catching on the alignment face (little piece in front of it that reinforces the bolt catch), so I smoothed and polished both surfaces.  Got it to move smoother into the positive (upwards) position.  Noticed a little rounding of the edge of the bolt, so cut into the face of the bolt as little as I could and made sure the corner was flat and 90 deg.  I didn't polish the surface for fear of making it too sensitive again.  I think it was catching, then throwing the bolt on the return from recoil.

Worked on test on 2 diff mags.  I'll see if it's reliable.

BTW, there are 2 levers inside the mag.  One transfers the bb follower's motion to the second, second transfers motion to the bolt catch lower plate (part of the bolt catch).

Can do pictures tomorrow if it'll help.

Edited by Carny, 12 July 2012 - 07:43 PM.


#15 BoobieM4H

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Posted 12 July 2012 - 07:55 PM

 Carny, on 12 July 2012 - 07:40 PM, said:

Fixed it, I think.  Agreed, there's not a lot of material there to catch the bolt.  

The bolt catch was catching on the alignment face (little piece in front of it that reinforces the bolt catch), so I smoothed and polished both surfaces.  Got it to move smoother into the positive (upwards) position.  Noticed a little rounding of the edge of the bolt, so cut into the face of the bolt as little as I could and made sure the corner was flat and 90 deg.  I didn't polish the surface for fear of making it too sensitive again.  I think it was catching, then throwing the bolt on the return from recoil.

Worked on test on 2 diff mags.  I'll see if it's reliable.

BTW, there are 2 levers inside the mag.  One transfers the bb follower's motion to the second, second transfers motion to the bolt catch lower plate (part of the bolt catch).

Can do pictures tomorrow if it'll help.

I had to square off the bolt face because it rounded it off when I first got the gun..it'll probably be on on going thing with grinding/filing it square.

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#16 R_King91303

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Posted 12 July 2012 - 09:29 PM

 BoobieM4H, on 12 July 2012 - 04:06 PM, said:

Any lever inside the mag can be removed to disable bolt catch function. If I were to want to disable it I would remove the lever that is moved by the bb follower..and leave the lever that pushes up on bolt catch in..removing the lever that pushes the bolt catch would leave a gap (hole) there and would be an ideal place for debris to go into.

True that the BB follower arm can be removed and eliminate the gap that would be created (in addition to the BB follower itself also being removed). However, no matter how slim the mathematical odds are, with the recoil and general jostling of the gun it would still be possible for the arm to pop up and engage the bolt stop. IMO, removing the  bolt stop arm would be the most certain way to prevent unintentional engagement for the purposes of dry firing demonstration.


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#17 BoobieM4H

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Posted 12 July 2012 - 09:52 PM

 R_King91303, on 12 July 2012 - 09:29 PM, said:


True that the BB follower arm can be removed and eliminate the gap that would be created (in addition to the BB follower itself also being removed). However, no matter how slim the mathematical odds are, with the recoil and general jostling of the gun it would still be possible for the arm to pop up and engage the bolt stop. IMO, removing the  bolt stop arm would be the most certain way to prevent unintentional engagement for the purposes of dry firing demonstration.


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The bolt catch is held in place by a detent pin with a spring behind it..that's why the bolt catch "clicks" when engaged/disengaged. I don't think the bolt catch will just jump up.

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#18 Jakeedaman21

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Posted 13 July 2012 - 07:13 AM

Mine tends to have a mind of its own, but that's because of the heavy B.A.D. Lever hanging on it.

#19 Epitaph

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Posted 16 July 2012 - 05:05 PM

My LM4 as well as a team mates suffered from the same problem over the weekend. Both rifles have had about the same number of rounds through - under 600 I would guess.. very disappointed with the way the stop is designed. I do not want to have to grind down my bolt carrier every 500-600 rounds just so the thing will catch on an empty mag, that's just ridiculous. I'm looking into doing Boobie's mod to see if that'll be a more permanent solution.

Edited by Epitaph, 16 July 2012 - 05:06 PM.


#20 TheSneak

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Posted 19 July 2012 - 02:10 PM

I had a completely different issue at first, but it then developed into this problem.

At first I was having issues with the bolt locking back when the mag was still full, almost consistently every two rounds. But only 2 of my 3 mags were behaving like this. These were the PMAGs I bought at the same time as my rifle. Upon further investigation, I noticed the springs are slightly weaker in those mags. But that still didn't explain why the bolt locked back when it wasn't supposed to.

So I took the mags in to the shop I bought them from, they tested them in their display model without any issues. I then went home and tried to replicate the behavior, but couldn't. Instead, the mags weren't causing the bolt to lock back at all, just as everyone else here described. So I opened the gun up and inspected everything, not really knowing what I was looking for. Lubed everything up, mostly the lever that locks the bolt back, thinking it was the issue. No results.

Took the gun back to the shop. They decide to replace the bolt because of some unusual wear and mushrooming at the front of the bolt. I test the gun in the shop, works great. They say that because of the high heat in our region, it could be effecting the way the gun functions. Now I am hoping that the problem doesn't come back. Will test this weekend or next hopefully.

Only used Green Gas, bought with gun. No mods whatsoever. Bone Stock.
Bought: July 10th 2012.
Took mags to shop on 16th.
Took back gun on 17th.
Got gun back on 18th.




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