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Posted: 1/27/2024 4:47:27 PM EDT
[Last Edit: 556sniper]
My 14.5 Mod 2 carbine with p/w nt4 mams shit the bed today at a local shoot. I have had this gun for awhile both with and without the nt4 with no issues. Was running it unsuppressed today and gun was clean and properly lubed. I tried PMC xtac, Norma 556 fmj, Fiocchi 223 and IMI m193 and regular m193 all which used to cycled perfectly before. Out of nowhere I got weak ejection then FTE's & FTF's then some light primer strikes to the point now where it wont fire. Running KAC lower with factory HH buffer and spring. I do notice ALOT of carbon build up forward of the Mod 2 gas block and the outer locking ring which also extends up the barrel. Any of you guys run into an issue like this? Would like to explore avenues before trying to deal with KAC RMA service because its well out of warranty and I will probably have to bear all the costs of repair. Any input is greatly appriciated.
  
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Posted: 1/27/2024 4:56:52 PM EDT
[#1]
Their RMA service has been excellent in my experience. I wouldn't hesitate to reach out. Worst case, you get the RMA process going and if you get a fix here you don't have to use it.
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USA
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Posted: 1/27/2024 5:14:20 PM EDT
[#2]
Weld’s going to have to come out to service the gas system.
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Posted: 1/27/2024 6:09:01 PM EDT
[#3]
Can you tell if the castle nut is loose? An enterprising individual could fabricobble up a line wrench style tool to reach down in there and tighten it up.
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Posted: 1/27/2024 8:19:59 PM EDT
[#4]
Take a look at the BCG and ensure that the gas key is still properly secured and not obstructed before you disassemble the gas system.
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Posted: 1/27/2024 8:49:10 PM EDT
[#5]
Quote HistoryOriginally Posted By SecretSquirell: Can you tell if the castle nut is loose? An enterprising individual could fabricobble up a line wrench style tool to reach down in there and tighten it up. I know a guy who made a wrench to tighten a loose nut on a barrel with a pinned muzzle device. It can be done. |
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Posted: 1/27/2024 9:08:55 PM EDT
[#6]
Sounds like something acutely changed, like a broken gas key screw. Try a different BCG if you have one.
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Posted: 1/27/2024 9:10:41 PM EDT
[#7]
Quote HistoryOriginally Posted By Tejas1836: Sounds like something acutely changed, like a broken gas key screw. Try a different BCG if you have one. Thats my next move. I have a spare carrier and E3 bolt I will test out 2moro. |
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Posted: 1/27/2024 10:16:36 PM EDT
[#8]
Quote HistoryOriginally Posted By FRBaseball: Take a look at the BCG and ensure that the gas key is still properly secured and not obstructed before you disassemble the gas system. Fantastic advice. I had a gas key problem (broken gas key fasteners) with a sandcutter carrier on my CQB mod 2. KAC fixed it pretty quick and no cost to me. |
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Posted: 1/27/2024 11:43:39 PM EDT
[#9]
Quote HistoryOriginally Posted By KSPeacekeeper: Fantastic advice. I had a gas key problem (broken gas key fasteners) with a sandcutter carrier on my CQB mod 2. KAC fixed it pretty quick and no cost to me. Quote HistoryOriginally Posted By KSPeacekeeper: Originally Posted By FRBaseball: Take a look at the BCG and ensure that the gas key is still properly secured and not obstructed before you disassemble the gas system. Fantastic advice. I had a gas key problem (broken gas key fasteners) with a sandcutter carrier on my CQB mod 2. KAC fixed it pretty quick and no cost to me. Thank you for your input but upon visable inspection both gas key screws are their and are staked. Unless they have broken inside I see no evidence of any broken parts either. Its the standard non sandcutter carrier and the gas rings, firing pin all appear intact as well. Definitely going to test the upper with my spare carrier and bolt tommorow hopefully that will help determine whats wrong. |
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UT, USA
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Posted: 1/28/2024 12:36:43 AM EDT
[#10]
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Posted: 1/29/2024 5:31:28 PM EDT
[#11]
Quote HistoryOriginally Posted By ClangClang: [email protected] Just got an email from them my upper is over a year old so I will have to pay for all the repairs out of pocket! I'm ready to throw this goddamn upper in a lake. I've had nothing but issues with the mod 2 I've been trying to buy a field repair kit for 2 years! I'm really getting fucking pissed off and about it because it's a paperweight without these proprietary spare parts that I can never fucking buy! Anyone you guys in this KAC group have one you're willing to part with please IM me. |
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Posted: 1/29/2024 6:04:21 PM EDT
[#12]
First post: I have had this gun for awhile both with and without the nt4 with no issues.
Latest post: I've had nothing but issues with the mod 2 Which is it? And how is a FRK going to fix your cycling issues? |
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Posted: 1/29/2024 6:11:42 PM EDT
[Last Edit: 556sniper]
[#13]
Quote HistoryOriginally Posted By FRBaseball: First post: I have had this gun for awhile both with and without the nt4 with no issues. Latest post: I've had nothing but issues with the mod 2 Which is it? And how is a FRK going to fix your cycling issues? I ran it for a long time without issue. However I didn't want to write a crazy long email to KAC. But I have had small issues recently with the 14.5 here and there that have added up to it being unreliable. But this latest case it just stopped working. Yeah I get it, in my verbiage it can be confusing but sometimes we Overlook the little things here and there but then think back after something catastrophic has happened that yeah this thing did have problems and maybe wasn't GTG like I thought it was. I'll own that FRK will help because I have a spare KAC carrier and a spare KAC Bolt but I do not have a spare firing pin or any of the other parts to rebuild the existing Bolt if one of those parts ends up being the problem |
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Posted: 1/30/2024 6:09:46 AM EDT
[#14]
It looks to me like the gas block castle nut has backed off.
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Posted: 1/30/2024 7:47:02 AM EDT
[Last Edit: Tejas1836]
[#15]
Quote HistoryOriginally Posted By 556sniper: I ran it for a long time without issue. However I didn't want to write a crazy long email to KAC. But I have had small issues recently with the 14.5 here and there that have added up to it being unreliable. But this latest case it just stopped working. Yeah I get it, in my verbiage it can be confusing but sometimes we Overlook the little things here and there but then think back after something catastrophic has happened that yeah this thing did have problems and maybe wasn't GTG like I thought it was. I'll own that FRK will help because I have a spare KAC carrier and a spare KAC Bolt but I do not have a spare firing pin or any of the other parts to rebuild the existing Bolt if one of those parts ends up being the problem KAC BC is generic carrier. Have you tried a different one yet? @556sniper |
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USA
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Posted: 1/30/2024 5:06:27 PM EDT
[#16]
Snap a picture of the castle nut/block between the mlok slots
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Posted: 1/30/2024 8:12:48 PM EDT
[#17]
Stripped all the rattlecan off and scrubbed the hell out of everything. Haven't been able to shoot it with the spare bolt and carrier yet. Took some pics of the gas block area, not sure if the gap on the tube is normal or not.
 
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Posted: 1/30/2024 11:44:17 PM EDT
[#18]
If you tap on your gas tube inside the upper receiver, does it move?
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Posted: 1/31/2024 7:07:23 AM EDT
[#19]
Quote HistoryOriginally Posted By flg23: If you tap on your gas tube inside the upper receiver, does it move? It does not. Gas tube and all the other components seem to be tight with no movement or rattling. |
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USA
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Posted: 1/31/2024 7:24:42 AM EDT
[Last Edit: battlemidget]
[#20]
Can you trombone the upper?
Remove the upper, remove bcg and charging handle from upper, put your mouth on the barrel and with your free hand (use a rag if needed), block the chamber while fluting the gas tube with a finger so you can feel the air as you blow into the barrel (depending on muzzle device, either cup it with your hand or tape off the ports). Be sure to stop by your LGS and demonstrate your new skill. |
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Posted: 1/31/2024 8:00:47 AM EDT
[#21]
PM me if you need a field repair kit. I’m not thrilled about giving one up, but if it’s determined you need a part, I’ll help you out.
Regardless, it sounds like a gas problem. Isolate whether it’s the carrier or the upper, then narrow it down from there. I’ve seen bits of brass/primer work their way into gas keys before, and broken carrier key screws that you couldn’t visually tell were broken until applying torque to them. Point is, it may not be blatantly obvious, but these are simple machines and frankly there’s only a few components that can cause what has happened. |
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Posted: 1/31/2024 9:34:02 AM EDT
[Last Edit: 556sniper]
[#22]
Quote HistoryOriginally Posted By Marksman14: PM me if you need a field repair kit. I’m not thrilled about giving one up, but if it’s determined you need a part, I’ll help you out. Regardless, it sounds like a gas problem. Isolate whether it’s the carrier or the upper, then narrow it down from there. I’ve seen bits of brass/primer work their way into gas keys before, and broken carrier key screws that you couldn’t visually tell were broken until applying torque to them. Point is, it may not be blatantly obvious, but these are simple machines and frankly there’s only a few components that can cause what has happened. I appreciate your insight. Today I should finally get a chance to test fire it with my spare E3 bolt and carrier. I ended up spending the last couple days stripping the rattle can paint job off and completely scrubbing the inside and out to help in pinpointing a problem area. I'm hoping it's as simple as something I overlooked in my diagnosis. But I am appreciating all the help from you guys in this KAC group helped me get this sucker running again. |
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TX, USA
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Posted: 1/31/2024 2:47:32 PM EDT
[#23]
Interested in seeing if the other BCG solves your issue. I have one that I ran FA on pretty frequently to test cans and the gas block nut did back off which surprised me. Only took about 500 rounds on a brand new upper. Removed-locktite-reappled with correct torque spec. I didn't have the issue you have im just speaking to the fact that yes the mod 2 gas blocks will back off.
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FL, USA
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Posted: 1/31/2024 4:34:41 PM EDT
[#24]
Quote HistoryOriginally Posted By CSGroup: Interested in seeing if the other BCG solves your issue. I have one that I ran FA on pretty frequently to test cans and the gas block nut did back off which surprised me. Only took about 500 rounds on a brand new upper. Removed-locktite-reappled with correct torque spec. I didn't have the issue you have im just speaking to the fact that yes the mod 2 gas blocks will back off. The Mod 2 gas block nut will only back off is not properly installed. We have humans performing that task, and humans can make mistakes. We have literally thousands of full-auto Mod 2 gas system guns out in the world in the hands of professional forces at extremely high rounds counts that do not see any indication of loss of torque at the gas block. KAC will fix these issues if present. Likewise, the gas key on the AR carrier is a problem point, it takes very little to lose the gas seal at the key. We have seen issues in the past, especially with the increased pressure at the key as results from shorter gas systems. If you can check that with a "known good" carrier, you can isolate the problem. As with anything in the system, if it isn't right we will fix it. |
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TX, USA
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Posted: 1/31/2024 6:09:45 PM EDT
[#25]
I agree with you 100% Jack- my comment was not a knock on KAC at all. I was just pointing out that from the factory it is possible for a gas block nut to back off after extreme courses of fire. Most uppers are fine but it does happen. Personally once I have added locktite and reapplied the nut with proper torque specs I have never had one back off.
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Posted: 1/31/2024 8:13:03 PM EDT
[#26]
I Citrus stripped the rattle can paint and soaked the gas tube, gas key and buffer tube overnight in solvent. When I scraped out and banged the gas key area a big glob of carbon nestiness came out of it as well as some nastiness in the back of the buffer tube. I've replaced the factory spring with a white spring Co and Lube the hell out of everything with Wilson lightweight oil and used my spare carrier. I just left the range and it ran flawlessly with 4 different kinds of ammo. I then tried the original carrier and it too ran perfect. Looks like I was the asshole for not cleaning properly and the blame solely lies with the end user once again. Never would I think a carbon fouling booger blob in the gas key area would be the culprit. Still scratching my head over the light primer strikes but perhaps some crud was blowing back in the firing pin Channel. Nonetheless I'm extremely thankful for all those who chimed in help diagnose the problem.
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Posted: 1/31/2024 10:22:52 PM EDT
[#27]
It’s a wonder these gas keys don’t build up carbon blockages more often than they do.
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Posted: 2/1/2024 10:08:04 AM EDT
[#28]
Quote HistoryOriginally Posted By 556sniper: I Citrus stripped the rattle can paint and soaked the gas tube, gas key and buffer tube overnight in solvent. When I scraped out and banged the gas key area a big glob of carbon nestiness came out of it as well as some nastiness in the back of the buffer tube. I've replaced the factory spring with a white spring Co and Lube the hell out of everything with Wilson lightweight oil and used my spare carrier. I just left the range and it ran flawlessly with 4 different kinds of ammo. I then tried the original carrier and it too ran perfect. Looks like I was the asshole for not cleaning properly and the blame solely lies with the end user once again. Never would I think a carbon fouling booger blob in the gas key area would be the culprit. Still scratching my head over the light primer strikes but perhaps some crud was blowing back in the firing pin Channel. Nonetheless I'm extremely thankful for all those who chimed in help diagnose the problem. Glad it worked out! I'm glad it was something simple like that versus a parts breakage or something that would have required a trip to KAC and or removal of your perm'ed muzzle device. I'm not sure if this is what has helped me avoid situations like this, but I am very strategic with where I lube these things. Everything gets a light coat of oil for corrosion resistance, and any excess is largely wiped off. Then on any contact areas (BCG rails, cam pin, raised area on the bolt that rides in the carrier) I use a good amount of a thicker lube like cherry balmz, or lately, ALG very thin grease. Those stay put and dont wander around were I don't want them, IE in the firing pin channel (which I would assume some lube/carbon softened up and slowed down your firing pin), or somehow work its way into the gas key/tube area and again create a sludge. I've had great luck lubing like this and running my rifles to higher round counts without having to wipe anything down, add lube etc. |
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FL, USA
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Posted: 2/1/2024 10:36:53 AM EDT
[#29]
Quote HistoryOriginally Posted By 556sniper: I Citrus stripped the rattle can paint and soaked the gas tube, gas key and buffer tube overnight in solvent. When I scraped out and banged the gas key area a big glob of carbon nestiness came out of it as well as some nastiness in the back of the buffer tube. I've replaced the factory spring with a white spring Co and Lube the hell out of everything with Wilson lightweight oil and used my spare carrier. I just left the range and it ran flawlessly with 4 different kinds of ammo. I then tried the original carrier and it too ran perfect. Looks like I was the asshole for not cleaning properly and the blame solely lies with the end user once again. Never would I think a carbon fouling booger blob in the gas key area would be the culprit. Still scratching my head over the light primer strikes but perhaps some crud was blowing back in the firing pin Channel. Nonetheless I'm extremely thankful for all those who chimed in help diagnose the problem. For CLP, I highly recommend something from the MIL-PRF-63460F approved list. I have been very happy with the G96 product for this. |
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Posted: 2/2/2024 6:39:18 AM EDT
[#30]
Quote HistoryOriginally Posted By Jack_L: For CLP, I highly recommend something from the MIL-PRF-63460F approved list. I have been very happy with the G96 product for this. Good to know, I will switch over to the G96 CLP. Thanks Jack |
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MI, USA
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Posted: 2/5/2024 11:04:23 AM EDT
[Last Edit: DetroitSounds]
[#31]
Quote HistoryOriginally Posted By 556sniper: Good to know, I will switch over to the G96 CLP. Thanks Jack .02 - I had some sluggish performance a few years back in my mod 2 11.5 w/ sand cutter. I was using Cherry balm. Jack recommended G96, which I've been using since. I much prefer the standard carrier, and G96. Nothing but smooth sailing over the last 15k-20k rounds through the 11.5 & 14.5. That includes 1000 round days with no wiping or lubing to get to the finish line. Glad you got it worked out. |
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Posted: 2/9/2024 8:40:04 AM EDT
[#32]
Quote HistoryOriginally Posted By 556sniper: I Citrus stripped the rattle can paint and soaked the gas tube, gas key and buffer tube overnight in solvent. When I scraped out and banged the gas key area a big glob of carbon nestiness came out of it as well as some nastiness in the back of the buffer tube. I've replaced the factory spring with a white spring Co and Lube the hell out of everything with Wilson lightweight oil and used my spare carrier. I just left the range and it ran flawlessly with 4 different kinds of ammo. I then tried the original carrier and it too ran perfect. Looks like I was the asshole for not cleaning properly and the blame solely lies with the end user once again. Never would I think a carbon fouling booger blob in the gas key area would be the culprit. Still scratching my head over the light primer strikes but perhaps some crud was blowing back in the firing pin Channel. Nonetheless I'm extremely thankful for all those who chimed in help diagnose the problem. Glad you got it figured out. It sounds like the problem may have been some kind of blockage within the gas key. |
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VA, USA
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Posted: 2/9/2024 8:48:57 AM EDT
[Last Edit: thedownzero]
[#33]
Whew! Good thing, now you can continue to be proud of your KAC ownership and retain your avatar that advertises just that.
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Posted: 2/9/2024 11:54:27 AM EDT
[#34]
Quote HistoryOriginally Posted By thedownzero: Whew! Good thing, now you can continue to be proud of your KAC ownership and retain your avatar that advertises just that. Yeah man! Even if the Mod 2 had to go back to KAC I still would have retained my Fanboy status. I got pissy because of the possible pin and weld removal and frustration of aquiring a field repair kit. All my other KAC stuff runs like a top and are the pride of my fleet. Definitely wouldn't become a hater over something stupid like this, no decal scraping neccesary 🤣 |
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