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Posted: 8/4/2022 7:29:36 PM EDT
[#1]
If you plan on getting rid of the URX4, I'll take it. I've been looking to replace my Aero handguard on my 18" 6.5 build
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Posted: 8/4/2022 7:33:59 PM EDT
[#2]
Quote HistoryQuoted: If you plan on getting rid of the URX4, I'll take it. I've been looking to replace my Aero handguard on my 18" 6.5 build Definitely don't want to get rid of the URX4. I just had it and a receiver set cerakoted. I just need a barrel with a smaller diameter towards the rear. |
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Posted: 8/6/2022 4:49:10 AM EDT
[#3]
i just went and measured an AR-10 barrel extension. 1.19". so 1.18" is in the ball-park for normal AR-10.
nvm. I think I don't understand the SR-25 URX4 mounting system. |
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Posted: 8/6/2022 11:27:01 AM EDT
[#4]
The shank diameter of the X-Caliber barrels are 1.150". I don't know if that is enough of a difference though.
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Posted: 8/9/2022 10:32:38 AM EDT
[#5]
The Criterion Hybrid fits just fine, in 6.5 CM.
Edit: looks like their 308 hybrid 16” also has a rifle length gas system. However, looking at both the hybrid and ADM barrel profiles, I’m surprised that the URX4 didn’t fit on the ADM profile. Both the ADM and Hybrid seem to be the diameter of the barrel extension, at the base of the barrel, which the URX 4 threads should clear easily because the threads are a larger diameter than the OD of the receiver extension. 6.5 CM, 16”, rifle length gas |
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Posted: 8/9/2022 10:44:28 AM EDT
[#6]
Quoted: I purchased a URX4 and ADM/Criterion 16" barrel for an AR10 build. Unfortunately, the URX4 will not fit over the end of the barrel near the extension, due to the barrel diameter. Does anyone have any recommendations for a 16" barrel with a rifle length gas system? The diameter of the barrel at the rear of the ADM/Criterion is approximately 1.18". Are you sure you don’t have an SR15 URX4? The inner diameter of the SR25 URX4 threads should be ~1.37” if I remember right, just like normal large frame AR handguard barrel nut threads. That gives plenty of space for 1.18” barrel thickness. |
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Posted: 8/9/2022 10:45:19 AM EDT
[#7]
Quote HistoryQuoted: The Criterion Hybrid fits just fine, in 6.5 CM. Edit: looks like their 308 hybrid 16” also has a rifle length gas system. However, looking at both the hybrid and ADM barrel profiles, I’m surprised that the URX4 didn’t fit on the ADM profile. Both the ADM and Hybrid seem to be the diameter of the barrel extension, at the base of the barrel, which the URX 4 threads should clear easily because the threads are a larger diameter than the OD of the receiver extension. 6.5 CM, 16”, rifle length gas https://i.ibb.co/88NXFMw/7-CA7-CCA2-1604-458-C-8-FF2-F4-CCA1-B95325.jpg Nice stick. Is that a Wilson Combat receiver set? How do you like it? Did you use their lpk? Working on a similar build. |
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Posted: 8/9/2022 10:53:41 AM EDT
[#8]
Quote HistoryQuoted: Nice stick. Is that a Wilson Combat receiver set? How do you like it? Did you use their lpk? Working on a similar build. Thanks. Yup, and the upper is their “lightweight” version. I used their LPK and a JP high pressure FMOS BCG. Though I’m sure their BCG is good quality like the rest of their stuff. I did swap the safety for a Badger Ordnance and put in a Geissele SSA-E trigger. I have no complaints with the Wilson setup. It is a good value, especially if you can do a mil or similar discount. I previously had an LMT MARS-H lower but it just wasn’t worth the price. I really don’t need full AMBI, and the AMBI bolt catch actually interfered and wouldn’t work with non-LMT uppers. Very happy to have switched to the Wilson. Fit and finish were wonderful and everything went together swimmingly. Plus, it saves a decent chunk of weight over the LMT without feeling like a flimsy ultralight build. |
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Posted: 8/9/2022 11:15:13 AM EDT
[#9]
Quote HistoryQuoted: Are you sure you don’t have an SR15 URX4? The inner diameter of the SR25 URX4 threads should be ~1.37” if I remember right, just like normal large frame AR handguard barrel nut threads. That gives plenty of space for 1.18” barrel thickness. This. Does the URX4 thread onto the upper receiver without the barrel installed? |
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Posted: 8/9/2022 11:34:11 AM EDT
[#10]
Quote HistoryQuoted: Are you sure you don’t have an SR15 URX4? The inner diameter of the SR25 URX4 threads should be ~1.37” if I remember right, just like normal large frame AR handguard barrel nut threads. That gives plenty of space for 1.18” barrel thickness. It’s definitely the SR25 version. P/N 31887. It’s not the threads that are the issue. There is a lip past the threads, where the QD mount is, that is hanging up in the rear of the barrel. The handguard threads onto the upper fine with the barrel not present. ETA: Here’s a photo showing the lip I am referencing.  Attached File |
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Posted: 8/9/2022 12:04:01 PM EDT
[#11]
Quote HistoryQuoted: It’s definitely the SR25 version. P/N 31887. It’s not the threads that are the issue. There is a lip past the threads, where the QD mount is, that is hanging up in the rear of the barrel. The handguard threads onto the upper fine with the barrel not present. ETA: Here’s a photo showing the lip I am referencing. https://www.ar15.com/media/mediaFiles/414212/6FC31693-9B5F-4D49-9573-595F7F475DFB_jpe-2482833.JPG Ahh. I wish I could easily take mine off to measure my barrel and inside the handguard. All I can say is the hybrid profile barrel fits in my URX4. Criterion shows that their 6.5 and 308 Hybrid profile barrels have the same external dimensions. Your URX4 would need to have clearance for a 1.200” outer diameter in front of the receiver extension, which my URX4 does. But if the ADM is only 1.18” and it still doesn’t fit, then I think something may be off with your URX4.  Do you have a way to measure that barrel nut lip inner diameter? |
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Posted: 8/9/2022 1:22:44 PM EDT
[#12]
Quote HistoryQuoted: Ahh. I wish I could easily take mine off to measure my barrel and inside the handguard. All I can say is the hybrid profile barrel fits in my URX4. Criterion shows that their 6.5 and 308 Hybrid profile barrels have the same external dimensions. Your URX4 would need to have clearance for a 1.200” outer diameter in front of the receiver extension, which my URX4 does. But if the ADM is only 1.18” and it still doesn’t fit, then I think something may be off with your URX4. https://criterionbarrels.com/wp-content/uploads/2019/08/AR10-HYR-1536x227.jpg Do you have a way to measure that barrel nut lip inner diameter? Unfortunately, I don’t. I sent an email to KAC to see what their thoughts are. ADM confirmed that my measurements were consistent with their barrels. |
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Posted: 8/9/2022 2:16:34 PM EDT
[#13]
Quote HistoryQuoted: Unfortunately, I don’t. I sent an email to KAC to see what their thoughts are. ADM confirmed that my measurements were consistent with their barrels. Best of luck. Worst case, I bet you could get that inner section bored out a thousandth of an inch or whatever is necessary. |
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Posted: 8/9/2022 2:16:46 PM EDT
[#14]
Maybe without the receiver you could vertically insert the barrel from the threaded end of the rail. Use some Dykem or mark the tapered portion of the barrel forward of the shank with a Sharpie. Twist the barrel, measure at the interference marks with calipers. Not entirely accurate, but might give you a better idea of the dimensional differences.
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Posted: 8/9/2022 8:09:15 PM EDT
[#15]
I think SR25 barrels are thinner just in front of the receiver. I’ve seen URX 3.1 barrel nuts having to be skimmed for non KAC barrels to fit. Wonder if the same applies to URX4. @unclemoak calls it out on his site.
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Posted: 8/10/2022 12:13:20 AM EDT
[#16]
Quote HistoryQuoted: I think SR25 barrels are thinner just in front of the receiver. I've seen URX 3.1 barrel nuts having to be skimmed for non KAC barrels to fit. Wonder if the same applies to URX4. @unclemoak calls it out on his site. it is an issue with URX 2/3, but I haven't seen it with a URX 4 though. Seems a little odd to me and maybe worth digging a little deeper on what the root cause of the issue is. |
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Posted: 8/12/2022 2:41:48 PM EDT
[#17]
I received a response from KAC. They stated the inside of the handguard in that area should be 1.2" +/- .02" in diameter.
They also stated they cannot guarantee function with other manufacturers parts. It looks like I may have to have the barrel or handguard machined to work. |
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