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Posted: 1/23/2021 5:06:18 PM EDT
[#1]
Is there a burr on the back of the bolt carrier?
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Posted: 1/23/2021 5:16:32 PM EDT
[#2]
Quote HistoryQuoted: Is there a burr on the back of the bolt carrier? darn, you must be right seems a little sharp. Is there any info on how to do this? My carrier is a KAC sandcutter and dont want to ruin it |
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Posted: 1/23/2021 6:49:32 PM EDT
[#3]
Do you have a pic that is in focus?
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Posted: 1/23/2021 7:17:56 PM EDT
[#4]
Quote HistoryQuoted: darn, you must be right seems a little sharp. Is there any info on how to do this? My carrier is a KAC sandcutter and dont want to ruin it Carefully file down the sharp spot with a hand file. Don't attack it with a Dremel or anything, that's probably way overkill. https://www.harborfreight.com/hand-tools/planes-sanders-files/files-rasps/8-inch-flat-file-96626.html Just a few light strokes, check it for smoothness, again if necessary until the burr is gone. |
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Posted: 1/23/2021 7:20:16 PM EDT
[#5]
here is the better pic :
https://i.postimg.cc/k4BpH0pH/20210123-181501.jpg do you think the buffer is ruined? or still good? what if i got a sand stone (https://www.harborfreight.com/combination-sharpening-stone-62852.html) used some light soap/water or gun oil and put it on the back of the carrier/ sand stone moved the the backside of the LIGHTLY in a figure eight motion across the stone until smooth. |
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Posted: 1/23/2021 7:31:03 PM EDT
[#6]
Quote HistoryQuoted: here is the better pic : https://i.postimg.cc/k4BpH0pH/20210123-181501.jpg do you think the buffer is ruined? or still good? what if i got a sand stone (https://www.harborfreight.com/combination-sharpening-stone-62852.html) used some light soap/water or gun oil and put it on the back of the carrier/ sand stone moved the the backside of the LIGHTLY in a figure eight motion across the stone until smooth. The buffer will be fine. Those scratches will wear out eventually. I would not do anything to the buffer. A stone would work on the back of the carrier, but I would do it the way I suggested above, just filing out the burr, because ideally you want to smooth the burr out but you really don't want to remove any more material from the carrier than necessary. So using a stone on the whole surface may be more than you need. |
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Posted: 1/23/2021 7:32:19 PM EDT
[#7]
Can you post a pic of the back of the carrier? The 2nd pic of the buffer is much more clear.
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Posted: 1/23/2021 7:42:38 PM EDT
[#8]
Quote HistoryQuoted: Can you post a pic of the back of the carrier? The 2nd pic of the buffer is much more clear. sure: back of carrier https://i.postimg.cc/VvjQGyS8/20210123-183955.jpg just for fun here is my new build:  upper Geissele (g stamped) upper reciever Knights 12inch RAS rail Knights vertical foregrip Knights qdc muzzle (thing cost 3xx$) Knights sand cutter carrier Knights 30mm scope mount Vortex razor 1:6 gen2e Vortex front and rear flip up lens covers/protectors BCM bolt, cam, fire pin. Daniel defense grip and rip charging handle Daniel defense gas block(pinned onto barrel) Daniel defense gas tube Daniel defense 12.5 556 barrel (cold forged) Lower: BCM lower Geisele lower parts kit with the martine bolt catch SBA 3 brace Geissele buffer tube, geissele spring, geissele h3 buffer Geissele SD3G combat trigger Magpul grip |
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Posted: 1/23/2021 7:56:37 PM EDT
[#9]
Quote HistoryQuoted: The buffer will be fine. Those scratches will wear out eventually. I would not do anything to the buffer. A stone would work on the back of the carrier, but I would do it the way I suggested above, just filing out the burr, because ideally you want to smooth the burr out but you really don't want to remove any more material from the carrier than necessary. So using a stone on the whole surface may be more than you need. the only reason i m considering using the stone over a file is that it is really hard to see where the burr is. if i use it over the stone in a flat/light manner, hopefully the sharp spot would rubb off before anything else does. with direct filing with a file, i risk removing metal in a spot that may not be the actual culprit |
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Posted: 1/23/2021 7:58:45 PM EDT
[#10]
I see a small ding on the carrier at about 4 o'clock (from perspective of carrier upright), and possibly some sharp edges on the slot at the bottom (6 o'clock). Is that where you feel the burr? I'd carefully file out just the burr.
I've got this set of needle files which I use all the time: https://www.harborfreight.com/12-piece-needle-file-set-468.html Patience and caution is your friend. |
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Posted: 1/23/2021 8:02:13 PM EDT
[#11]
Quote HistoryQuoted: the only reason i m considering using the stone over a file is that it is really hard to see where the burr is. if i use it over the stone in a flat/light manner, hopefully the sharp spot would rubb off before anything else does. with direct filing with a file, i risk removing metal in a spot that may not be the actual culprit You don't need to see it, you should be able to feel it. The spot that is the culprit should catch and be scratchy, especially if you run your fingernail around the edge of the carrier. The burr is probably only a few thousands, so you really don't want to remove much material at all. |
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Posted: 1/23/2021 8:07:52 PM EDT
[#12]
Quote HistoryQuoted: You don't need to see it, you should be able to feel it. The spot that is the culprit should catch and be scratchy, especially if you run your fingernail around the edge of the carrier. The burr is probably only a few thousands, so you really don't want to remove much material at all. good eye, the 4oclock ding seems smooth. i tested and it is the 6oclock area that is causing the scratches. just hard to tell from exactly where. here is the area in which i know is cuasing the scratches https://i.postimg.cc/X7bpV4k9/20210123-183955.jpg |
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Posted: 1/23/2021 8:25:01 PM EDT
[#13]
Quote HistoryQuoted: good eye, the 4oclock ding seems smooth. i tested and it is the 6oclock area that is causing the scratches. just hard to tell from exactly where. here is the area in which i know is cuasing the scratches https://i.postimg.cc/X7bpV4k9/20210123-183955.jpg I kinda suspected it was around the slot. What I would do is just file off the three edges of the slot to smooth them out. Removing just that much material and in that location will not affect the length of the carrier, which is the dimension you don't want to alter. I think needle files are a pretty good tool for this kind of job. |
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Posted: 1/23/2021 8:26:48 PM EDT
[#14]
Quote HistoryQuoted: I kinda suspected it was around the slot. What I would do is just file off the three edges of the slot to smooth them out. Removing just that much material and in that location will not affect the length of the carrier, which is the dimension you don't want to alter. I think needle files are a pretty good tool for this kind of job. great idea. this is what i m going to do. what do you mean by the three sides? i m going to buy the needle files tomorrow and smooth it out. TY, greatful for people like you with good advice. |
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Posted: 1/23/2021 8:48:45 PM EDT
[#15]
Quote HistoryQuoted: great idea. this is what i m going to do. what do you mean by the three sides? i m going to buy the needle files tomorrow and smooth it out. TY, greatful for people like you with good advice. There are three edges to the slot, you basically just want to knock the corner off at the back so there are no sharp edges, round them off a little. |
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Posted: 1/23/2021 9:03:47 PM EDT
[#16]
 File where I marked in red. |
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Posted: 1/23/2021 9:17:56 PM EDT
[#17]
Quote Historyit feels a little pointy in this area too (blue). Can i hit that slightly too? 
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Posted: 1/23/2021 9:57:46 PM EDT
[#18]
Quote HistoryQuoted: it feels a little pointy in this area too (blue). Can i hit that slightly too? https://i.postimg.cc/zfQXgrZD/20210123-183955.jpg Yes, just round off that point a little. |
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Posted: 1/24/2021 12:20:55 PM EDT
[#19]
This is just my opinion, but that KAC carrier is worth a hell of a lot more than that buffer. I wouldn’t touch the carrier. Plus, the scratches go all the way to the very center of the buffer. The back of the carrier is open. It can’t move around enough to cause scratches all the way in the center of the buffer.
Test that out by removing the carrier and the buffer spring. Put the buffer in the receiver extension and push it back with the carrier. You shouldn’t be able to move the carrier around enough to create contact with the center of the buffer. Plus, keep in mind that the carrier slides along the bearing surfaces of the upper receiver, which will prevent the carrier from moving much at all. I don’t know what’s causing those scratches, but I’d bet it’s not the carrier. You could also try that carrier in another gun to see if it’s causing the same issue on a different buffer. |
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Posted: 1/24/2021 12:26:26 PM EDT
[#20]
Quote HistoryQuoted: This is just my opinion, but that KAC carrier is worth a hell of a lot more than that buffer. I wouldn’t touch the carrier. Plus, the scratches go all the way to the very center of the buffer. The back of the carrier is open. It can’t move around enough to cause scratches all the way in the center of the buffer. Test that out by removing the carrier and the buffer spring. Put the buffer in the receiver extension and push it back with the carrier. You shouldn’t be able to move the carrier around enough to create contact with the center of the buffer. Plus, keep in mind that the carrier slides along the bearing surfaces of the upper receiver, which will prevent the carrier from moving much at all. I don’t know what’s causing those scratches, but I’d bet it’s not the carrier. You could also try that carrier in another gun to see if it’s causing the same issue on a different buffer. I agree, those scratches don't seem consistent with the areas of the carrier that have been targeted. |
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Posted: 1/24/2021 2:15:16 PM EDT
[#21]
Quote HistoryQuoted: I agree, those scratches don't seem consistent with the areas of the carrier that have been targeted. Yes they do. The scratches to the center happen when the rifle is opened. As the upper tilts away from the lower the carrier rubs across the buffer. If there is a burr around the slot it would make scratches consistent with the pictures. Also if you look closely at the buffer a ring is being worn around the outer edge right where the slot in the carrier is. What else could it possibly be? Nothing but the back of the bolt carrier should be touching the buffer, right? |
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Posted: 1/24/2021 2:18:34 PM EDT
[#22]
Quote HistoryQuoted: This is just my opinion, but that KAC carrier is worth a hell of a lot more than that buffer. I wouldn’t touch the carrier. Plus, the scratches go all the way to the very center of the buffer. The back of the carrier is open. It can’t move around enough to cause scratches all the way in the center of the buffer. Test that out by removing the carrier and the buffer spring. Put the buffer in the receiver extension and push it back with the carrier. You shouldn’t be able to move the carrier around enough to create contact with the center of the buffer. Plus, keep in mind that the carrier slides along the bearing surfaces of the upper receiver, which will prevent the carrier from moving much at all. I don’t know what’s causing those scratches, but I’d bet it’s not the carrier. You could also try that carrier in another gun to see if it’s causing the same issue on a different buffer. As I said in my previous message, I think that the scratches to the center probably happen when the rifle is opened. Another thing to try to test whether it is the carrier by trying a different buffer in that rifle, you can get a cheap one for not much money. I don't think there is much risk of damaging the carrier with the tiny amount of filing that I suggested either. |
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Posted: 1/24/2021 3:56:37 PM EDT
[#23]
Quote HistoryQuoted: I agree, those scratches don't seem consistent with the areas of the carrier that have been targeted. scratches are from the carrier. i spun the buffer around on a fresh side and then open and closed the rifle. i was able to track down where on the carrier was causing the buffer to scratch by creating new scratches on the undisturbed side of the buffer.. if you look on the above photots, it was from the blue/red area that has been highlighted. |
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Posted: 1/24/2021 4:31:44 PM EDT
[#24]
Quote HistoryQuoted: scratches are from the carrier. i spun the buffer around on a fresh side and then open and closed the rifle. i was able to track down where on the carrier was causing the buffer to scratch by creating new scratches on the undisturbed side of the buffer.. if you look on the above photots, it was from the blue/red area that has been highlighted. I'm pretty sure if you can file off the burr and smooth up those sharp edges your problem will be solved. |
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Posted: 1/24/2021 4:32:54 PM EDT
[#25]
Quote HistoryQuoted: scratches are from the carrier. i spun the buffer around on a fresh side and then open and closed the rifle. i was able to track down where on the carrier was causing the buffer to scratch by creating new scratches on the undisturbed side of the buffer.. if you look on the above photots, it was from the blue/red area that has been highlighted. From opening the action? I can see that now. I was trying to figure out how that could happen from operation and it didn't add up. I see no harm in some 600 grit or finer and touching up the circumference. |
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Posted: 1/24/2021 4:44:37 PM EDT
[#26]
Don't forget that buffer moves (spins slightly) as it is in operation. So the scratches can appear in different places on the buffer face as well as occuring when the upper is opened.
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Posted: 1/24/2021 10:43:25 PM EDT
[#27]
Quote HistoryQuoted: As I said in my previous message, I think that the scratches to the center probably happen when the rifle is opened. Another thing to try to test whether it is the carrier by trying a different buffer in that rifle, you can get a cheap one for not much money. I don't think there is much risk of damaging the carrier with the tiny amount of filing that I suggested either. I missed that comment and didn’t even think about that. Good point. |
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Posted: 1/24/2021 11:55:20 PM EDT
[#28]
Quote HistoryQuoted: I missed that comment and didn’t even think about that. Good point. No problem, it took me a while thinking about it to figure it out myself. The initial post was a real head scratcher. |
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Posted: 1/25/2021 1:46:07 AM EDT
[#29]
The circular mark around the perimeter of the buffer is not normal. It looks like that the buffer is contacting the tip of the buffer retaining pin when it cycles forward. This should not happen when the upper and lower is assembled. Only when you pivot it open. Your carrier should stick out of the upper enough to push the buffer slightly back off of the retaining pin when you pivot it together.
I have seen this problem arise from time to time. It indicates that the hole drilled for the buffer retaining pin is out of spec. |
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Posted: 1/25/2021 2:15:33 AM EDT
[#30]
Quote HistoryQuoted: The circular mark around the perimeter of the buffer is not normal. It looks like that the buffer is contacting the tip of the buffer retaining pin when it cycles forward. This should not happen when the upper and lower is assembled. Only when you pivot it open. Your carrier should stick out of the upper enough to push the buffer slightly back off of the retaining pin when you pivot it together. I have seen this problem arise from time to time. It indicates that the hole drilled for the buffer retaining pin is out of spec. not sure what you mean by this. i am pretty sure all the marks seen on the buffer are from the carrier moving when the rifle is being opened and closed and not related to the cycling. the carrier was leaving marks on the outside and inside of the buffer. once the carrier moved, when rifle was being opening, it would start to scratch the buffer. the filing fixed it. |
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Posted: 1/25/2021 2:18:06 AM EDT
[#31]
looks like it is fixed now. i put in my bcm buffer and open and closed the rifle 10 times and i didnt see a single scratch.
i bought these files https://www.lowes.com/pd/Kobalt-8-in-Smooth-File-Set/999921002 and filed the edges that were rough (highlighted in blue/red in the photo posted before). The metal on the carrier is much harder then the metal on the files, so it took some time to file. I am honestly impressed by the metal on these carriers, the files can hardly scratch the carrier after several minutes of filing. Well all seems just fine now, ty to everyone who helped. Just ordered a new geissele buffer so i dont have to look at all these scratches. Plus i needed a h3 buffer and an h2 buffer and was tired of switching the buffer weights around. |
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Posted: 1/25/2021 2:45:17 AM EDT
[#32]
Quote HistoryQuoted: not sure what you mean by this. i am pretty sure all the marks seen on the buffer are from the carrier moving when the rifle is being opened and closed and not related to the cycling. the carrier was leaving marks on the outside and inside of the buffer. once the carrier moved, when rifle was being opening, it would start to scratch the buffer. the filing fixed it. I believe he is referring to what appears to be a slight peening around the perimeter of the buffer, which often happens from the buffer hitting the retainer upon return to battery as I tried to outline here  I have seen much worse and it likely isn't an issue |
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Posted: 1/25/2021 3:18:23 AM EDT
[#33]
I'm glad you got it. I was gonna help, but I wanted you to figure it out yourself.
 I figured the long scratches were coming from opening and closing. The perimeter marks can come from two different places. If the retaining pin hole is drilled too far to the rear, the carrier will fail to push the buffer off of the pin and the buffer will slam into the pin on every shot. In your case, it was probably from the burr on your carrier. And as was mentioned, the buffer will rotate in the extension causing the marks to appear along the whole edge if given enough shots. |
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Posted: 1/25/2021 3:34:44 AM EDT
[#34]
Quote HistoryQuoted: I'm glad you got it. I was gonna help, but I wanted you to figure it out yourself. I figured the long scratches were coming from opening and closing. The perimeter marks can come from two different places. If the retaining pin hole is drilled too far to the rear, the carrier will fail to push the buffer off of the pin and the buffer will slam into the pin on every shot. In your case, it was probably from the burr on your carrier. And as was mentioned, the buffer will rotate in the extension causing the marks to appear along the whole edge if given enough shots. i believe when i was closing/opening the the riffle, the carrier burr was clipping the buffer causing those perimeter scratches (also the scratches seem to be a few mm longer than the pin and thinner, so it doesnt line up that it came from the buffer hitting pin. i closed the rifle 3/4 of the way and peaked in, as best as i can tell, the carrier seems to give just enough pushback on the buffer to keep the tension off pin. |
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Posted: 1/25/2021 4:43:03 AM EDT
[#35]
Judging by the pic above, it looks like your pin hole is good and the buffer seems to be far enough foward to hit the carrier.
When the buffer is hitting the pin, it leaves more of a micro dent vs a scratch. And, if your carrier is pushing on the buffer when closed, there is no way for the buffer to hit the pin to leave a mark when cycled. |
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Posted: 1/25/2021 12:28:43 PM EDT
[#36]
Quote HistoryQuoted: not sure what you mean by this. i am pretty sure all the marks seen on the buffer are from the carrier moving when the rifle is being opened and closed and not related to the cycling. the carrier was leaving marks on the outside and inside of the buffer. once the carrier moved, when rifle was being opening, it would start to scratch the buffer. the filing fixed it. I'm not saying that you have this problem for sure. I'm saying that the marks on the perimeter of the buffer look suspicious. As another poster said- you will usually get 'micro-dents' on the face of the buffer. The fact that you do have scratches on the buffer from pivoting the rifle upper/lower together would indicate that there is some contact there, which is good.  |
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Posted: 1/25/2021 12:52:13 PM EDT
[#37]
Excellent pic showing the interface of the parts.
I think the op should now have a good understanding on how these parts play together. |
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Posted: 1/25/2021 2:36:17 PM EDT
[#38]
Quote HistoryQuoted: Excellent pic showing the interface of the parts. I think the op should now have a good understanding on how these parts play together. I agree, that pic illustrates exactly how those scratches could get on the buffer if there is a bur on the back of the carrier. |
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Posted: 1/25/2021 2:38:10 PM EDT
[#39]
Quote HistoryQuoted: looks like it is fixed now. i put in my bcm buffer and open and closed the rifle 10 times and i didnt see a single scratch. i bought these files https://www.lowes.com/pd/Kobalt-8-in-Smooth-File-Set/999921002 and filed the edges that were rough (highlighted in blue/red in the photo posted before). The metal on the carrier is much harder then the metal on the files, so it took some time to file. I am honestly impressed by the metal on these carriers, the files can hardly scratch the carrier after several minutes of filing. Well all seems just fine now, ty to everyone who helped. Just ordered a new geissele buffer so i dont have to look at all these scratches. Plus i needed a h3 buffer and an h2 buffer and was tired of switching the buffer weights around. I'm glad your issue is resolved. I honestly wouldn't hessitate to use that buffer, but if you needed a different weight anyway, that's cool. |
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Posted: 1/25/2021 2:46:20 PM EDT
[#40]
Great thread, I need to add some files to my tool set.
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