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Posted: 11/1/2025 9:59:16 AM EDT
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Here goes, I picked-up a Colt 9mm Carbine Model 6951. The price was SUPER CHEAP. But there are/were some issues. 1 - The Butt Stock is NOT Colt (looking for an actual Colt) 2 - PG is MagPul not Colt 3 - No-Name Carry Handle instead of the MagPul MBUS rear Sight. 4 - Missing FCG I corrected # 2, 3 & 4 All of that is Great, BUT the real problem is that the previous owner BUGGERED UP the Threads for the Flash Hider. The Flash Hider only screws on about .100" and he stacked 3 Crush Washers for the FH to butt against. What is the Thread Pitch on the Colt 9mm ? How do I fix this ? Any help would be GREATLY appreciated ! |
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Found this neat little chart. Do not know if it is accurate. Silencer Central flash hider thread pitch The chart shows 1/2” – 36 for the Colt 9 mm. |
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Originally Posted By jdtbone: Found this neat little chart. Do not know if it is accurate. Silencer Central flash hider thread pitch The chart shows 1/2” – 36 for the Colt 9 mm. Correct^^^ I didn't know this when I bought my NIB colt 9mm carbine. Had to buy a new piston for my can. Could be he has the wrong FH on it. A 1/2x28 piston & FH will thread about 3 turns before getting too tight on each other due to thread pitch. Get the correct 1/2x36 9mm FH and see if that fixes it. Colt (and a few others ) do the x36 so you don't put a 556 FH on the end for safety. |
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Originally Posted By Postal0311: Thread pattern is likely 1/2-36. Correct. All Colt 9mm carbines are and have been 1/2-36. I have had 2. |
"According to Argonne National Laboratory, it takes 100 pounds of battery in an EV to go a distance achieved by only one pound of gasoline in an ICE vehicle"
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Thanks' to everyone for the Thread Pitch info. Any suggestions as to how to fix the BUGGERED UP Threads on the Barrel Barrel Thread Pic I was thinking of sending it to JT and have him Cut (14.7-15"), Thread & P&W the FH. But, I would like to keep it as original as possible. I am looking for an actual Colt Carbine stock to replace the Aluminum Bushmaster I put on it (temporary/trade stock). |
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I can't see the pic even after logging in no big deal. I'd find out if the threads can be cleaned up before tossing money into a chop & pin. there are a few ways to clean up the threads all pretty cheap. You can use a file made for it. No ham fisting. Run it on a lathe with just a clean up pass. Maybe a die no idea if that 1/2x36 die is made or if it is inexpensive. Then buy a new correct FH the old one is probably either wrong or screwed up along with the muzzle threads. You might even be able to just screw a correct FH onto the muzzle. No idea see my 1st sentence! On a side note my teenage son loves ours and when ever we shoot 9mm pcc semi's he always grabs the Colt. |
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Also try a steel haired brush to clean up the burrs. The problem with pin and weld is if you want to run a suppressor later on (very great option with PCCs) it gets complicated unless you had the foresight to pin and weld a suppressor ready FH, of which most are proprietary unless its a 3-lug or such. |
"According to Argonne National Laboratory, it takes 100 pounds of battery in an EV to go a distance achieved by only one pound of gasoline in an ICE vehicle"
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Thank you to everyone for your ideas/suggestions. HUGE SHOUT-OUT & THANKS to gurn-blanston I have wanted a 9mm Colt AR for so long, but never pulled the trigger(I don't know why). This one came up and I didn't even think about it. Plus it cost less then a PSA DOE Upper. A No-Brainer |
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I would not worry about the grip. I would probably try running a clean up die on the threads and get the correct flash hider. I put a shorter barrel on mine with a 3lug. |
" Don't cry, nobody shoots Glocks anymore."
"But the new Admin. is a Master in IDPA"
"MASTER in IDPA..."
"is like C Class in IPSC!"
"But the new Admin. is a Master in IDPA"
"MASTER in IDPA..."
"is like C Class in IPSC!"
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OK , this is to finish out this Colt 9mm 6951. I ordered a reasonably priced (cheap) 1/2X36 UNS Tap & Die Set off amazon for $15.99. Chased the Barrel Threads with the Die, and it worked GREAT. A new Colt 9mm FH screwed on perfectly. Then I touched up the threads with a little Cold Blue. So now this Carbine is back to original configuration. I want to thank everyone for their suggestions. |
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Just a couple of tips from a guy who built a 9mm AR a while back from a Colt SMG parts kit. Make sure it has the spacer in the buffer tube. 9mm Colt ARs have a pretty violent action since they are blowback and the bolt hammers the bolt hold open catch. The 9mm AR doesn't need that much travel so installing the spacer (if missing) can help. Also, stainless hammer and trigger pins. You may or may not have a ramped bolt but either way stainless pins are the way to go. Colt changed the pins to stainless a long time ago because the violent action was breaking hammer pins. Enjoy that 9 mil. I absolutely love mine. Runs perfectly (which was somewhat of a miracle). Only issue I've had was magazine related. Last round nose up jam. |
'They who can give up essential liberty to purchase a little temporary safety, deserve neither liberty nor safety.'
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Originally Posted By Yorge9003: Also, stainless hammer and trigger pins. You may or may not have a ramped bolt but either way stainless pins are the way to go. Colt changed the pins to stainless a long time ago because the violent action was breaking hammer pins. No need for stainless pins, Use M16 hammer, but cut the tail off the hammer up to about where the auto lug would reside. What happens is when the bolt ride over hammer, the geometry push tail of hammer into the disconnector, and the hammer tries to lift at the hammer pin. ** 9mm here since mid-2003 |
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Originally Posted by Yorge9003: Make sure it has the spacer in the buffer tube. Funny thing, when I disassembled for inspection, the Buffer Spacer was installed Backwards. Don't know if that could cause problems, but I corrected it. Originally Posted by SBR7_11: No need for stainless pins, Use M16 hammer, but cut the tail off the hammer up to about where the auto lug would reside. What happens is when the bolt ride over hammer, the geometry push tail of hammer into the disconnector, and the hammer tries to lift at the hammer pin. I have a Colt Notched Hammer it it now. Will replace it with a Non-Notched Hammer. It has the original Bolt, not sure if it's Ramped or not. I will check. Thanks for all the suggestions. |
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Originally Posted By SBR7_11: No need for stainless pins, Use M16 hammer, but cut the tail off the hammer up to about where the auto lug would reside. What happens is when the bolt ride over hammer, the geometry push tail of hammer into the disconnector, and the hammer tries to lift at the hammer pin. ** 9mm here since mid-2003 Went and looked at my clone right after reading your reply and sure as hell it looks like the tail end of my hammer has been smashing in to the disconnector. Im running a Schmid FCG with an M-16 profile hammer and the original non ramped Colt bolt. Ive run it configured like factory (obviously minus select fire) and never had any issues but I can see where that constant smashing could break pins over time. I assume Colt used stainless pins as a band aid since a cut down hammer would interfere with having a sear catch on the hammer. Im going to cut the tail down a little and replace the disco. Affer next time at the range Ill take a look and see if it looks like its not hitting so hard any more. Thanks! I never thought of that since I never had any problems. Well, not yet. Lol! I just ran with stainless pins and never looked back. |
'They who can give up essential liberty to purchase a little temporary safety, deserve neither liberty nor safety.'
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Originally Posted By 1NAVYCHIEF-RET: OK , this is to finish out this Colt 9mm 6951. I ordered a reasonably priced (cheap) 1/2X36 UNS Tap & Die Set off amazon for $15.99. Chased the Barrel Threads with the Die, and it worked GREAT. A new Colt 9mm FH screwed on perfectly. Then I touched up the threads with a little Cold Blue. So now this Carbine is back to original configuration. I want to thank everyone for their suggestions. Sounds good! Glad the threads chased out OK and the previous owner didn't horse the flash hider on to the point more threads were ruined. 
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I'm getting down to the last box, the others have all been destroyed...
I'm getting down to the last box, the others have all been destroyed...
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Originally Posted By 1NAVYCHIEF-RET: Many Thanks to Yorge9003 & SBR7_11 for your info/suggestions. It does have SS Trigger & Hammer Pins. Currently looking for a true COLT M16 style Hammer that I could use (minus the Sear Notch). I just want to keep all the parts as much Colt as possible. When I got my SMG parts kit it came with the factory Colt tri-burst trigger group made by Schmid for Colt. (so my clone is technically an RO639 but I like to imagine its the RO635 because full auto is cooler) Obviously I wasn't going to run that so I got a new Schmid FCG. For a long, long time Schmid was the OEM manufacturer of Colts FCGs, both select fire and semi. At some point Colt dropped them and started using what appears to be investment cast parts from like India or something. I dont know if you remember but Colt had a huge recall because of issues with those parts. They are the hammers and triggers marked with just a number and some dots or something and IMHO they are garbage. If you want the hammer to have Colt markings you will need to find an older one. You can always get a Colt M-16 "C" marked hammer from Apex Gun Parts and grind the sear hook off. Last time I was on their web site they had late 70s Colt M-16 hammers in stock. Personally I would buy a new Schmid "Gun Nuts" GI fire control group. Its high quality and since Schmid was the OEM for Colt for many years it would still be considered "correct". The FCG comes in a cool little package that looks like a snack bag (like a bag of peaNUTS) and has USGI spec parts and springs. The disconnector is very well ground. Not stamped out like so many are. Being a GI trigger group its heavy but I find it feels pretty good. It has run flawlessly in my 9mm. I have that trigger group in my 635 clone, my M-16A2 clone and my GWOT M4 clone and they all feel pretty good for a single stage GI trigger group. Just use your stainless pins and after firing it a few times check and see if the tail of the hammer is smashing in to the disco and shave it down like SBR7_11 suggested earlier in the thread. If you go with Schmid get the "Gun Nuts GI fire control group". They have two other versions. One is cheaper but thats for gunsmith to do final grinding and polishing of the engagement surfaces and the other is a "Sporter" with the notched hammer that you do not want to use. I think the Schmid FCG is available at Optics Planet. After having written this novel (sorry, I get carried away) if you just want an M-16 style hammer and dont care who made it I probably have one sitting in my parts bin that I will send you for free. Also, I read your spacer was installed backwards. All I see that doing would be compressing the recoil spring a little more but since you put it back right its a non issue. |
'They who can give up essential liberty to purchase a little temporary safety, deserve neither liberty nor safety.'
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The bottom of the bolt contour is very important. The standard Colt 9 mm bolt does not have the same contour as the carrier used in a 5.56X45 upper. Without the ramped contour similar to the 5.56 carrier, the original style 9 mm bolt has a 90 degree angle from the bottom of the bolt to the firing pin. Because the 9mm bolt doesn’t have the ramp it pushes on the hammer, to cock the hammer, closer to the hammer pin. That puts more stress on the pin, but does slow the cyclic rate. That extra stress is why the hammer pins in the 9mm guns tend to snap in the center. It is my understanding that recent manufactured 9mm bolts now has a similar sloped ramp for the hammer like that of the rifle caliber bolt carriers. Scott |
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I use a CMC pcc trigger in my colt uses the two piece pins to hold the cassette in place the hammer doesn’t touch them. No issues at all with it. @3.5lbs single stage |
" Don't cry, nobody shoots Glocks anymore."
"But the new Admin. is a Master in IDPA"
"MASTER in IDPA..."
"is like C Class in IPSC!"
"But the new Admin. is a Master in IDPA"
"MASTER in IDPA..."
"is like C Class in IPSC!"
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