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Posted: 2/16/2026 3:57:34 PM EDT
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Does anyone have a picture of the 556 QDC CRS with the short collar installed and the suppressor mounted onto a rifle? If the shorter collar is used, is there a gap with non-cerakoted metal showing, either between the suppressor and the collar, or at the bottom end of the collar? I am asking as with 11.5" CQB the 556 QDC CRS doesn't appear to have enough clearance when mounted, so will have to shim or go with the replacement short collar from KAC, and am trying to decide between the two. |
| I went with the non-shroud collar. It's shorter at the bottom of the collar, not the top. The locking ring/threads are in the same location on both the collar and non-collar versions. The only difference is that after you put the silencer on the mount and tighten it down, you might see just a bit of the QDC interface at the rear of the silencer vs. the shroud version which provides a bit more coverage. |
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Originally Posted By Foundation: Does anyone have a picture of the 556 QDC CRS with the short collar installed and the suppressor mounted onto a rifle? If the shorter collar is used, is there a gap with non-cerakoted metal showing, either between the suppressor and the collar, or at the bottom end of the collar? I am asking as with 11.5" CQB the 556 QDC CRS doesn't appear to have enough clearance when mounted, so will have to shim or go with the replacement short collar from KAC, and am trying to decide between the two. Short collar with MCQ (would fit same as CRS) on Mod 2 CQB. Attached File Attached File Attached File Attached File |
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Glad you posted here, I’m currently in the same boat. I have a pending CRS-1 that I plan on swapping onto my Mod2 CQB that has worn a legacy QDC CQB for its entire life. There used to be a massive thread on this, and if I recall correctly there was some consternation over shimming vs changing collars. If it wasn’t for that thread, I would have just shimmed it and been done with it. I’ve never tried a shroud, but I’m open to trying one for mirage mitigation if I throw it on the 16”. Was some sort of consensus reached on a “better” option? Plan right now is to just use an accu-washer. The shroud isn’t enough of a factor to sway me one way or another. |
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Originally Posted By TNW: Glad you posted here, I’m currently in the same boat. I have a pending CRS-1 that I plan on swapping onto my Mod2 CQB that has worn a legacy QDC CQB for its entire life. There used to be a massive thread on this, and if I recall correctly there was some consternation over shimming vs changing collars. If it wasn’t for that thread, I would have just shimmed it and been done with it. I’ve never tried a shroud, but I’m open to trying one for mirage mitigation if I throw it on the 16”. Was some sort of consensus reached on a “better” option? Plan right now is to just use an accu-washer. The shroud isn’t enough of a factor to sway me one way or another. Shimming creates some tolerance stacking (probably minimal though), so IMO the “better” solution is to swap collars. KAC used to provide a free short collar with photo evidence of no clearance with the long collar, but not sure if they still do that or not. |
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Originally Posted By mdavis: Shimming creates some tolerance stacking (probably minimal though), so IMO the “better” solution is to swap collars. KAC used to provide a free short collar with photo evidence of no clearance with the long collar, but not sure if they still do that or not. Originally Posted By mdavis: Originally Posted By TNW: Glad you posted here, I’m currently in the same boat. I have a pending CRS-1 that I plan on swapping onto my Mod2 CQB that has worn a legacy QDC CQB for its entire life. There used to be a massive thread on this, and if I recall correctly there was some consternation over shimming vs changing collars. If it wasn’t for that thread, I would have just shimmed it and been done with it. I’ve never tried a shroud, but I’m open to trying one for mirage mitigation if I throw it on the 16”. Was some sort of consensus reached on a “better” option? Plan right now is to just use an accu-washer. The shroud isn’t enough of a factor to sway me one way or another. Shimming creates some tolerance stacking (probably minimal though), so IMO the “better” solution is to swap collars. KAC used to provide a free short collar with photo evidence of no clearance with the long collar, but not sure if they still do that or not. I have it on good authority that in a few months KAC will be releasing muzzle devices that will push the index pin a little further forward to solve this problem for people that don’t want switch to a tabbed upper receiver and URX6 combination. The new muzzle devices can be installed on Mod 2 guns and allow for the use of current generation suppressors with shroud compatible collars, all without extra shimming. |
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Originally Posted By mdavis: Shimming creates some tolerance stacking (probably minimal though), so IMO the “better” solution is to swap collars. KAC used to provide a free short collar with photo evidence of no clearance with the long collar, but not sure if they still do that or not. Originally Posted By mdavis: Shimming creates some tolerance stacking (probably minimal though), so IMO the “better” solution is to swap collars. KAC used to provide a free short collar with photo evidence of no clearance with the long collar, but not sure if they still do that or not. Originally Posted By agnisco: I have it on good authority that in a few months KAC will be releasing muzzle devices that will push the index pin a little further forward to solve this problem for people that don’t want switch to a tabbed upper receiver and URX6 combination. The new muzzle devices can be installed on Mod 2 guns and allow for the use of current generation suppressors with shroud compatible collars, all without extra shimming. Thanks for the responses. My intent with the accu-washer was to mitigate the tolerance stacking - one seems better than several. My main concern was it requiring too thick of a shim for my liking, even if only one. It could be turd word, but I was tracking that the replacement collars were no longer free. A good step one would have been confirming this with someone who actually knows, so I’ll reach out tomorrow. If I could get my hands on a URX6 or FF RAS5, I’d also be happy with those. This is a notched upper. Doesn’t seem like those are available though. |
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Originally Posted By TNW: Thanks for the responses. My intent with the accu-washer was to mitigate the tolerance stacking - one seems better than several. My main concern was it requiring too thick of a shim for my liking, even if only one. It could be turd word, but I was tracking that the replacement collars were no longer free. A good step one would have been confirming this with someone who actually knows, so I’ll reach out tomorrow. If I could get my hands on a URX6 or FF RAS5, I’d also be happy with those. This is a notched upper. Doesn’t seem like those are available though. RAS5 would have the same issue (length is the same as URX4 I recall). URX6 would work though. |
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Originally Posted By TNW: Thanks for the responses. My intent with the accu-washer was to mitigate the tolerance stacking - one seems better than several. My main concern was it requiring too thick of a shim for my liking, even if only one. It could be turd word, but I was tracking that the replacement collars were no longer free. A good step one would have been confirming this with someone who actually knows, so I’ll reach out tomorrow. If I could get my hands on a URX6 or FF RAS5, I’d also be happy with those. This is a notched upper. Doesn’t seem like those are available though. If you have a CQB upper then they're still doing those for free. They're only charging if you have like a MK18 or other non-KAC upper. |
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Originally Posted By mdavis: I went with the non-shroud collar. It's shorter at the bottom of the collar, not the top. The locking ring/threads are in the same location on both the collar and non-collar versions. The only difference is that after you put the silencer on the mount and tighten it down, you might see just a bit of the QDC interface at the rear of the silencer vs. the shroud version which provides a bit more coverage. Thank you for responding and providing this information. |
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Originally Posted By agnisco: Short collar with MCQ (would fit same as CRS) on Mod 2 CQB. https://www.ar15.com/media/mediaFiles/133944/IMG_2267_jpeg-3714992.JPG https://www.ar15.com/media/mediaFiles/133944/IMG_2268_jpeg-3714994.JPG https://www.ar15.com/media/mediaFiles/133944/IMG_2269_jpeg-3714995.JPG https://www.ar15.com/media/mediaFiles/133944/IMG_2270_jpeg-3714996.JPG Originally Posted By agnisco: Originally Posted By Foundation: Does anyone have a picture of the 556 QDC CRS with the short collar installed and the suppressor mounted onto a rifle? If the shorter collar is used, is there a gap with non-cerakoted metal showing, either between the suppressor and the collar, or at the bottom end of the collar? I am asking as with 11.5" CQB the 556 QDC CRS doesn't appear to have enough clearance when mounted, so will have to shim or go with the replacement short collar from KAC, and am trying to decide between the two. Short collar with MCQ (would fit same as CRS) on Mod 2 CQB. https://www.ar15.com/media/mediaFiles/133944/IMG_2267_jpeg-3714992.JPG https://www.ar15.com/media/mediaFiles/133944/IMG_2268_jpeg-3714994.JPG https://www.ar15.com/media/mediaFiles/133944/IMG_2269_jpeg-3714995.JPG https://www.ar15.com/media/mediaFiles/133944/IMG_2270_jpeg-3714996.JPG Thank you for providing these photographs. Looks good. I think I will go with the shorter collar. |
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Originally Posted By agnisco: I have it on good authority that in a few months KAC will be releasing muzzle devices that will push the index pin a little further forward to solve this problem for people that don’t want switch to a tabbed upper receiver and URX6 combination. The new muzzle devices can be installed on Mod 2 guns and allow for the use of current generation suppressors with shroud compatible collars, all without extra shimming. And here is a terrible link to a pic I got of the MD in question from the KAC discord.... 
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Well I spoke with the good folks at KAC on the phone/over email today about options, they were very helpful. Ultimately decided on sending it in for a URX6 replacement as they’re out of short collars for my can, and I didn’t want to risk voiding the warranty on the CRS based on the amount of shims that they said could/would be required. There was no ETA given/available on the new MDs. They got me RMA information quickly, and I got it in the mail tonight. Should arrive Monday, and they said 10 working days. Received really good service today. One understandable thing that I was unaware of, is that they will not work on guns that have non-KAC components. I have a Radian Raptor charging handle and DD chrome carrier. Honestly not even sure where the OEMs are at this point. They decided they would replace the handguard, but they will not perform a function check or anything. In the future, I’ll be keeping my OEM parts separate - or just leave them OEM because they’re great anyways. I just like the easy to clean carrier and feel/vents of the Raptor SD. |
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Originally Posted By TNW: Well I spoke with the good folks at KAC on the phone/over email today about options, they were very helpful. Ultimately decided on sending it in for a URX6 replacement as they’re out of short collars for my can, and I didn’t want to risk voiding the warranty on the CRS based on the amount of shims that they said could/would be required. There was no ETA given/available on the new MDs. They got me RMA information quickly, and I got it in the mail tonight. Should arrive Monday, and they said 10 working days. Received really good service today. One understandable thing that I was unaware of, is that they will not work on guns that have non-KAC components. I have a Radian Raptor charging handle and DD chrome carrier. Honestly not even sure where the OEMs are at this point. They decided they would replace the handguard, but they will not perform a function check or anything. In the future, I’ll be keeping my OEM parts separate - or just leave them OEM because they’re great anyways. I just like the easy to clean carrier and feel/vents of the Raptor SD. Interesting. I took the advice of another fellow KAC enthusiast from the MCQ thread and reached out to KAC customer service as well. Just finished up the emails back and forth today. They asked for serial of the rifle and suppressor and sent me a form to fill in to send me a short collar. They said it would be at no cost but did not indicate a lead time. Thy also explained the short collar and MCQ-1 will not work with the shroud, p/n 118957. They explained the URX6 option as well if I wanted to use the MCQ-1 with shroud on the Mod 2 11.5" but referred me to the list of KAC dealers to get the work done and explained I would have to pay for that. So are you saying they issued a RMA and you are sending it back to KAC mother ship for the URX6 rail swap? |
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Originally Posted By ChandlerKJ: Interesting. I took the advice of another fellow KAC enthusiast from the MCQ thread and reached out to KAC customer service as well. Just finished up the emails back and forth today. They asked for serial of the rifle and suppressor and sent me a form to fill in to send me a short collar. They said it would be at no cost but did not indicate a lead time. Thy also explained the short collar and MCQ-1 will not work with the shroud, p/n 118957. They explained the URX6 option as well if I wanted to use the MCQ-1 with shroud on the Mod 2 11.5" but referred me to the list of KAC dealers to get the work done and explained I would have to pay for that. So are you saying they issued a RMA and you are sending it back to KAC mother ship for the URX6 rail swap? That’s correct. It will run about $450. The short collar would have been nice and easy, but as mentioned, it’s looking like it will be a while. |
| Got my rifle back from KAC today, and they really hooked it up. I gave it a quick wipe before sending, but what I got back is pristine. The URX6 and CRS fit perfectly, the FH no longer has carbon caked on it, and they included shims with the URX4 return. All in all, they exceeded expectations. With the new bolt I feel like I basically have a KS3 upper now. It looks like a brand new gun. |
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Originally Posted By TNW: Got my rifle back from KAC today, and they really hooked it up. I gave it a quick wipe before sending, but what I got back is pristine. The URX6 and CRS fit perfectly, the FH no longer has carbon caked on it, and they included shims with the URX4 return. All in all, they exceeded expectations. With the new bolt I feel like I basically have a KS3 upper now. It looks like a brand new gun. It is a KS-3 upper now. |
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Originally Posted By TNW: Got my rifle back from KAC today, and they really hooked it up. I gave it a quick wipe before sending, but what I got back is pristine. The URX6 and CRS fit perfectly, the FH no longer has carbon caked on it, and they included shims with the URX4 return. All in all, they exceeded expectations. With the new bolt I feel like I basically have a KS3 upper now. It looks like a brand new gun. Impossible. KAC has terrible customer service and hates you. 
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Originally Posted By TNW: Got my rifle back from KAC today, and they really hooked it up. I gave it a quick wipe before sending, but what I got back is pristine. The URX6 and CRS fit perfectly, the FH no longer has carbon caked on it, and they included shims with the URX4 return. All in all, they exceeded expectations. With the new bolt I feel like I basically have a KS3 upper now. It looks like a brand new gun. That’s great to hear. KAC directed me to their dealer list if I decided to choose the URX6 option but were clear that would be on me to pay for. I opted for the collar swap and they sent a form to fill out to initiate that process. I’m sure it will ship when they get sufficient stock lined up. Sounds like you literally got the white glove treatment! |
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