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Posted: 4/25/2010 7:19:37 PM EDT
I am having issues with the bolt catch not engaging after the last shot, any help would be appreciated.
I am going to try a heavier buffer this week, as soon as it comes in. Otherwise, I am out of ideas. Since I have it more often with higher pressure loads, could the bolt be bouncing off completely compressed buffer spring cause the bolt carrier to return to battery too fast? Could the high pressure of the 5.56 load be leaking more through a hole in the gas block/gas tube connection causing shorter stroking? Rifle Details:
Edit: I forgot to mention that I am also running a Magpul BAD which I have read might affect the bolt catch |
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Why is it loose? Do you have it installed correctly. Will it catch on an empty mag? I only mean to say that there is no friction in its movement, It is not loose like wiggling all over. It works every time when I pull the bolt back by hand on an empty mag. |
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A couple of things you mentioned could have me running in different directions since they could all be related to your problem.
I am going to assume that the weapon is assembled correctly, the gas tube does not bind on the carrier key, all of the bolt gas rings are staggered, etc. Multiple things can cause the bolt catch to fail to lock. I am sure you already have looked at these, but I am going to pretend like I am starting from scratch. The most common cause of this failure is the Magazine––insure this is not the cause before moving on. Magazines have to be in perfect order to make a MAD extended bolt catch work. Undergassing, Short stroking, and Overgassing can all cause this failure. Sticking, bent, or loose bolt catch lever can cause it also. SInce this is a newly assembled weapon, have you physically checked the bold catch's little nub actually is long enough to engage with a magazine follower? Remove the upper receiver, put a magazine in the well, and insure the catch is long enough to engage the magazine follower. The small residual carbon leak on the gas block. How small is it? Are we talking barely perceptable after numerous rounds being fired, or leaves a nice clearly visible spot of black carbon after only a few rounds? The former is permissible, the later would require correction––but unless it was a pretty substancial leak, it should not be causing this problem by itself. The loose bolt catch; do you mean that it moves freely up and down, without binding, or does it physically wobble from side to side? Former permissible, later would require correction. Nothing wrong with the bolt face? Pull the charging handle all the way to the rear, look in the ejection port and make sure the bolt face can travel to the rear far enough––at least 1/4 inch behind the bolt catch, or about even with the rear of the ejection port hole. Manually lock the bolt catch and look in through the ejection port, does it engage correctly, not tipped forward? Does the bolt catch have the little protrusion that is engaged by the magazine? Magpul BAD; it can make a small problem worse. The additional weight and momentum required to move the extended bolt catch can exacerbate an existing problem. If the weapon and magazines were operating correctly, the MAD should work––just slightly off and the MAD can make the problem more pronounced. You can try it without the MAD, and if it works, fine? But, I think that is only fixing a symptom of the problem and not the real problem. What bolt carrier do you have? Full auto, or semi––there is a weight difference. Buffer: In looking at your parts, you state you have a standard buffer, you mean a carbine buffer (which is required for your set-up) correct? It has to be a carbine buffer, I dont know how you could get a standard rifle buffer in there. Which carbine buffer? H, H2, H3? Does the recoil feel more pronounced? Buffer bottoming out hard in the extension tube? Are there any tattle-tale marks on the urethane end of the buffer, indicating it bottoming out hard? It should just barely kiss the receiver extension. If the answer is yes to those, I think your diagnosis to go to a heavier buffer is correct. You seem pretty sure that you are not undergassing and I think your assumption that your buffer is bouncing the bolt back too fast is correct. The Magpul BAD is probably contributing to this as the magazine follower cannot push the catch, and the additional weight of the MAD, up fast enough. Hope that helps |
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The BAD lever is the likely culprit.... it slows the catch down a bit.
If you really like the BAD, try running a heavier buffer to slow things down a bit. If that DOESN'T work, remove the BAD and try it. The BAD is a nifty device, but it does cause this problem for a lot of people... |
| i would recommend the spikes st-t2 buffer, its a great product. It should slow the action enough to allow the bolt catch to move. as said, the weight and leverage of the bad will slow down the lever movement. Or you install a stronger spring in the bolt catch. That should work too. |
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i would recommend the spikes st-t2 buffer, its a great product. It should slow the action enough to allow the bolt catch to move. as said, the weight and leverage of the bad will slow down the lever movement. Or you install a stronger spring in the bolt catch. That should work too. I am way ahead of you... my ST-T2 should be delivered today. I will report back... |
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Possible that the BAD lever is causing your problem. Take it off and see if the problem persists, if the problem goes away and you want to keep the BAD change the Bolt Catch. What bolt catch would work? I don't think that would fix this. I think I would have to slow down the rearward travel of the bolt carrier to give the bolt catch more time to engage. |
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Or you install a stronger spring in the bolt catch. That should work too. I confess to being a noob, but wouldn't a stronger bolt catch spring give it more force to counteract the magazine spring, and, therefore, slower or less likely to rise and catch the bolt on the last round? |
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I am going to assume that the weapon is assembled correctly, the gas tube does not bind on the carrier key, all of the bolt gas rings are staggered, etc. All assumptions are correct. Quoted:
The most common cause of this failure is the Magazine––insure this is not the cause before moving on. Magazines have to be in perfect order to make a MAD extended bolt catch work. I did have some issues with my PMAGs rubbing against the bolt catch ramp. I dremeled the mags about 1/32" and now there is no engagement issues. I have this issue with all mags though. Polymer, steel, aluminum, 20rd, 30rd. Quoted:
Sticking, bent, or loose bolt catch lever can cause it also. SInce this is a newly assembled weapon, have you physically checked the bold catch's little nub actually is long enough to engage with a magazine follower? Remove the upper receiver, put a magazine in the well, and insure the catch is long enough to engage the magazine follower. All function tests work fine with an empty mag. Quoted:
The small residual carbon leak on the gas block. How small is it? Are we talking barely perceptable after numerous rounds being fired, or leaves a nice clearly visible spot of black carbon after only a few rounds? The former is permissible, the later would require correction––but unless it was a pretty substancial leak, it should not be causing this problem by itself. It was enough to notice only when I took off the hand guard, but it did not get all over the hand guard. It extends about 4" behind the gas block. I have an extra gas block roll pin I am going to replace the existing one with to see if that seals it up. Quoted:
The loose bolt catch; do you mean that it moves freely up and down, without binding, or does it physically wobble from side to side? Former permissible, later would require correction. It moves freely, it is not wobbly. I guess "loose" is a confusing word for this. Sorry. Quoted:
Nothing wrong with the bolt face? No. It is a brand new BCM MP HP bolt. It looks good. I do get some brass flakes there from extraction (also indicating overgassing). I clean it religiously. Quoted:
Pull the charging handle all the way to the rear, look in the ejection port and make sure the bolt face can travel to the rear far enough––at least 1/4 inch behind the bolt catch, or about even with the rear of the ejection port hole. Manually lock the bolt catch and look in through the ejection port, does it engage correctly, not tipped forward? Does the bolt catch have the little protrusion that is engaged by the magazine? As I said, all function tests pass just fine. The bolt does lock back when live firing some of the time. Quoted:
Magpul BAD; it can make a small problem worse. The additional weight and momentum required to move the extended bolt catch can exacerbate an existing problem. If the weapon and magazines were operating correctly, the MAD should work––just slightly off and the MAD can make the problem more pronounced. You can try it without the MAD, and if it works, fine? But, I think that is only fixing a symptom of the problem and not the real problem. I think this is very likely the issue. The MAD is making a small gas problem more apparent. Quoted:
What bolt carrier do you have? Full auto, or semi––there is a weight difference. BCM M16 (full auto) Quoted:
Buffer: In looking at your parts, you state you have a standard buffer, you mean a carbine buffer (which is required for your set-up) correct? It has to be a carbine buffer, I dont know how you could get a standard rifle buffer in there. Which carbine buffer? H, H2, H3? Does the recoil feel more pronounced? I have the BCM standard carbine buffer, not H1/2/3. http://www.bravocompanyusa.com/Carbine-Buffer-p/buffer%20carbine.htm I am installing the spikes buffer today. Quoted:
Buffer bottoming out hard in the extension tube? How could I tell this? Recoil is very light. Much lighter than a standard carbine length M4gery with A2 flash hider (mine uses the PWS FSC556) Quoted:
Are there any tattle-tale marks on the urethane end of the buffer, indicating it bottoming out hard? It should just barely kiss the receiver extension. If the answer is yes to those, I think your diagnosis to go to a heavier buffer is correct. I have not looked for that, I will check the old buffer when I put in the new one. Quoted:
You seem pretty sure that you are not undergassing and I think your assumption that your buffer is bouncing the bolt back too fast is correct. The Magpul BAD is probably contributing to this as the magazine follower cannot push the catch, and the additional weight of the MAD, up fast enough. Hope that helps Thanks! |
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Or you install a stronger spring in the bolt catch. That should work too. I confess to being a noob, but wouldn't a stronger bolt catch spring give it more force to counteract the magazine spring, and, therefore, slower or less likely to rise and catch the bolt on the last round? You are completely correct. A stronger mag spring would help. A stronger bolt catch spring would hurt the issue. Some people cut a few coils off of the bolt catch spring to help this issue. However, I am not to that point yet. Thanks! |
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