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Posted: 1/25/2014 9:15:51 AM EST
[Last Edit: 1/25/2014 9:16:53 AM EST by rncbinc]
I didn't know where this build fit in so I will put it here. I was getting bored waiting for ATF paperwork on my other projects so I went looking for something to do. I recently purchased an AT-4 spent shell to hang on my office wall o' swag and I thought it would make a cool sub-caliber rifle. I remember training on one back when I was in the Corps and thought it would be a fun project. Here is what I have so far:
I have a few questions. Does anyone know if you can just buy the 9mm back end shown in the training manuals? If no, does any one have blueprints for the 9mm trainer module? If no, I will have to build one from scratch. Thanks in advance for any assistance or ideas.

Link Posted: 1/26/2014 5:47:22 PM EST
[Last Edit: 1/26/2014 5:48:42 PM EST by agb104983]
No, the firing machanisms are not for sale anywhere that I'm aware of. I think there's at least one legally owned AT4 9mm trainer that an ordnance dealer was selling awhile back. But other than that, nothing. I've always wanted to own/make one so I'll be following this thread closely. I even have a bit of the special 9mm tracer ammo used in the AT4's to match the trajectory of an AT4 projectile. I probably have around 5 different types of AT4 tubes in my ordnance collection.
Link Posted: 1/26/2014 5:54:24 PM EST
[Last Edit: 1/26/2014 5:54:54 PM EST by agb104983]
If I remember correctly, the tube itself and trigger mechanism are different on the 9mm trainers compared to the standard AT4 tubes. But if you are making your own breach piece/gun from the start, this shouldn't be an issue.
Link Posted: 1/27/2014 7:00:05 AM EST
Yes, I think I will have to make my own breech loading 9 mm. I am going to use a simple AR15 barrel and rotating lock for the breach, like the real trainer. I took apart the firing mechanism and it looks like they used a simple 45/45 to get the horizontal movement to vertical to hit the firing primer on the missile. I think something like a spring loaded firing pin and armature would work. I'll post up pictures when I get the basic idea down.
Link Posted: 1/27/2014 8:46:50 AM EST
I have a spent tube that I bought years ago. Always thought eventually I would set it up to fire model rockets. Just never have gotten around to it.
Link Posted: 1/27/2014 9:26:27 AM EST
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By rncbinc:
Yes, I think I will have to make my own breech loading 9 mm. I am going to use a simple AR15 barrel and rotating lock for the breach, like the real trainer. I took apart the firing mechanism and it looks like they used a simple 45/45 to get the horizontal movement to vertical to hit the firing primer on the missile. I think something like a spring loaded firing pin and armature would work. I'll post up pictures when I get the basic idea down.
View Quote



Sounds great. Keep me updated and I'll try to help anyway I can.
Link Posted: 1/27/2014 1:33:56 PM EST
Just some NFA questions perhaps you have looked into. If you used a sub caliber device (not a the signaling device sub caliber launcher for the M72 see link below) wouldn't the tube need to be registered as a destructive device like a 37 mm flare launcher and a beehive round? Otherwise would the sub-caliber device be an aow if it doesn't meet the emergency signalling device standard?

http://www.ar15.com/forums/t_6_2/383605_My_new_Rocket_Launcher__M72_LAW_with_M190_adapter.html
Link Posted: 1/27/2014 1:47:15 PM EST
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By mliann22:
Just some NFA questions perhaps you have looked into. If you used a sub caliber device (not a the signaling device sub caliber launcher for the M72 see link below) wouldn't the tube need to be registered as a destructive device like a 37 mm flare launcher and a beehive round? Otherwise would the sub-caliber device be an aow if it doesn't meet the emergency signalling device standard?

http://www.ar15.com/forums/t_6_2/383605_My_new_Rocket_Launcher__M72_LAW_with_M190_adapter.html
View Quote



I'm guessing that assuming a barrel length over 16 inches(not sure if the tube would count as the barrel length or if the actual 9mm barrel inside the tube has to be over 16 inches) and an overall length over 26 inches, the AT4 would be classified as a rifle. You can build a rifle without ATF approval.
Link Posted: 1/28/2014 3:49:29 AM EST
I have clicked the subscribe button. OP, don't let me down.
Link Posted: 1/28/2014 5:30:39 AM EST
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By therex:
I have clicked the subscribe button. OP, don't let me down.
View Quote


Indeed! Excellent project. I once shot more of those trainers than I can imagine, had a guy behind me just reloading after every shot burning up all the excess 9mm. Good times, I love the hollow pop noise it makes. Shooting a real one was more fun though. Good luck OP, I look forward to seeing your progress!
Link Posted: 1/28/2014 8:25:33 AM EST
Yes, the barrel inside the tube will be 16" AR15 9mm carbine barrel, so it would be a rifle length. The tube is just the "stock and trigger" I suppose you could use it w/o the tube, but then it is more like a pistol, both can be made w/o BAFTE issues. Either way, I believe it is legal to build and own w/o special registration but I would check your local laws too. I am LEO in a gun friendly state so there will be no problems for me except finding good 9mm tracer to shoot. I think the AT-4 9mm were sub-sonic to match the trajectory of the missile. Nice to have, but not necessary for shooting card board cutouts of tanks.
Link Posted: 1/28/2014 9:19:54 AM EST
TAG!!!!!!
Link Posted: 1/28/2014 4:19:20 PM EST
Sweet, tagged for updates.
Link Posted: 1/30/2014 6:44:47 AM EST
Ok, I have basic concept for the 9mm. The firing bolt will be inserted into the breach and rotated 90 deg. to the lock position. The shooter will cock, aim, depress the safety and fire the gun. After I disassembled the firing mechanism I found out that the mechanism has about 1.5" of travel from cocked to fired. I am going to use a bar and armature attached to the firing mechanism tube and hidden under the removable end where to 2 bolts and safety pin are. The idea is to have the force from the firing mechanism drive a sear and sear carrier assembly to the rear while compressing a firing pin spring. Once the assembly reaches the end of it's travel the sear will trip, releasing the firing pin. That of course with strike the primer firing the gun. Lock time should be les than 1/2 second Here is a rough drawing of the idea with the front disk and missile tube omitted. What do you all think? Also a member brought up the bore-sight issue. I think adjustment screws on the forward barrel disk will give me enough room to get the sights and gun shooting on target at about 100 yards.

Link Posted: 2/1/2014 4:53:19 AM EST
Here are a couple of photos of the firing pin mechanism removed. Simple but effective use of the spring energy seems to be the key here.



Link Posted: 2/1/2014 3:02:42 PM EST
Very cool. I'm keeping a close eye on this.
Link Posted: 2/2/2014 6:44:06 AM EST
Originally Posted By rncbinc:
I didn't know where this build fit in so I will put it here. I was getting bored waiting for ATF paperwork on my other projects so I went looking for something to do. I recently purchased an AT-4 spent shell to hang on my office wall o' swag and I thought it would make a cool sub-caliber rifle. I remember training on one back when I was in the Corps and thought it would be a fun project. Here is what I have so far:
I have a few questions. Does anyone know if you can just buy the 9mm back end shown in the training manuals? If no, does any one have blueprints for the 9mm trainer module? If no, I will have to build one from scratch. Thanks in advance for any assistance or ideas.

http://i861.photobucket.com/albums/ab177/rncbinc/IMG_2699_zps27088f11.jpg
View Quote


I believe we met yesterday. I was with a guy looking at some paintball stuff.
Link Posted: 2/3/2014 5:02:11 AM EST
Yes we did, you gents had some interesting stories, I hope your friend has success in his new project. I will shoot you all an email when we get a range day set for the next machinegun shoot.
Link Posted: 2/8/2014 11:13:04 AM EST
Today I worked a little on the 3D model for the barrel side of the gun. I think it will be simple but effective. A standard barrel nut will hold the barrel in place.



Link Posted: 2/8/2014 12:44:27 PM EST
If you build these, I think there would be a small market for them.
Link Posted: 2/8/2014 12:59:15 PM EST
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By jagdkommando:
If you build these, I think there would be a small market for them.
View Quote


Not worth the investment for getting the licenses required unless he already has one. That said, I'd buy one,
Link Posted: 2/8/2014 3:26:35 PM EST
theres a place in California that sell the bolts, I saw them listed as an unknown bolt for 50 bucks, I knew what it was but never bothered to email them. i'd have to do some digging to find them. I think it was dealers warehouse or some shit but i'm not 100% on that.
Link Posted: 2/9/2014 9:33:20 AM EST
That would be an awesome find! Post it up if you can.
Link Posted: 2/9/2014 9:44:17 AM EST
I found a Dealers Warehouse Gun Shop in Modesto CA....but no AT4 parts on their list in the web sight. How long ago was it, maybe they sold them or took them down cause no one wanted them. I will call them.
Link Posted: 2/9/2014 9:27:25 PM EST
I don't really remember who had them but I do recall the place was in California. What companies other than dealers warehouse and northridge deal in gun parts in Cali? iIRC the firm was in SoCal, it may be a wild goose chase but I vividly remember seeing them in their miscellaneous parts section. I tried finding the company but had no luck, I do remember they would have an obscure ad in shotgun news once in a while.
Link Posted: 2/10/2014 8:11:50 AM EST
So I think I have settled on a one piece receiver design and a two piece bolt carrier. I will draw up a simple bolt face later, but here is how is will look. It looks like production of the prototype is going to run around $500 including the purchase of a 9mm barrel, so not to bad.


Link Posted: 2/10/2014 10:43:05 AM EST
Looks great!!!
Link Posted: 2/11/2014 6:26:59 AM EST
Today I took apart the rear cone. If you soak it in hot water for 10 minutes it will loosen the glue and you can remove it without damage. I took some measurements of the cone and came up with these adaptations. I think it is starting to look more like a factory M287 unit except for the trigger arm. More pictures of course.







Link Posted: 2/11/2014 6:34:41 AM EST
Tagging because this is a kickass project.
Link Posted: 2/11/2014 12:30:48 PM EST
I also worked out smoothing out the bolt. I will have to send a lot of the work out to a CNC shop so I will be doing 5 of each part. PM if you want to get in on the project.



Link Posted: 2/12/2014 8:04:54 AM EST
Where can one find an AT4 tube?
Link Posted: 2/12/2014 8:30:21 AM EST
once this is built, can you post the completed design or offer to sell them for 10 bucks? I would LOVE to have an AT4 simulator AOW that I could take to the range, It would live in its own pelican case (OD green, obligatory stickers obviously), and I would scare the SHIT out of people at the range...
Link Posted: 2/12/2014 8:49:05 AM EST
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By RaptorFuel:
Where can one find an AT4 tube?
View Quote


Gunbroker, the EE, Ebay etc... they pop up fairly frequently, unfortunately the airsoft kids have made their cost skyrocket.
Link Posted: 2/12/2014 9:25:50 AM EST
I need 1 or 2 more people to jump in and I can start ordering parts! I am almost done with the design, all I have left are the small pieces in the bolt. I also ordered an AR15 9mm extractor. I think I will just copy the AR15 9mm bolt face to match up with the AR15 9mm barrel. I am calling mine a "single shot bolt action rifle" because the barrel is at least 16" long and when you attach it to the "stock" tube it is well over 26" long so I don't think it necessary to get the $5 stamp LOL. You can bet the guys at your local range will get a kick out of it for sure. I'm going to put reactive target mix, the sensitive stuff, behind cardboard cut outs of tanks and shoot tracers at them till the go boom! Just one more station to add to the annual pumpkin shoot.
Link Posted: 2/12/2014 9:51:25 AM EST
This is pretty awesome. I loved shooting the trainers in the Army. I've had a tube for the longest time and wanted something like this. Keep up the awesome work!
Link Posted: 2/14/2014 5:51:27 AM EST
once this is built, can you post the completed design or offer to sell them for 10 bucks? I would LOVE to have an AT4 simulator AOW that I could take to the range, It would live in its own pelican case (OD green, obligatory stickers obviously), and I would scare the SHIT out of people at the range
View Quote


Once I have it all done, I will send you the DXF. if you have access to CNC it will be an easy weekend project.
Link Posted: 2/14/2014 8:07:23 AM EST
how in the hell would you ship one??? put a lable on the side of it and a few stamps and walk into the post ofice??
Link Posted: 2/14/2014 8:28:05 AM EST
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By Slug-O:
how in the hell would you ship one??? put a lable on the side of it and a few stamps and walk into the post ofice??
View Quote


Ship an AT4 tube or ship the parts he's making?
Link Posted: 2/14/2014 8:53:47 AM EST
Same way it got to me, UPS in a big brown box.
Link Posted: 2/14/2014 1:14:03 PM EST
I have a "mint" AT4 tube and a friend wanted it. A few stamps should do it, right???
Link Posted: 2/14/2014 5:40:43 PM EST
[Last Edit: 2/14/2014 5:53:21 PM EST by agb104983]
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By Slug-O:
I have a "mint" AT4 tube and a friend wanted it. A few stamps should do it, right???
View Quote

Pretty much. I've either shipped or had shipped to me everything from demilled missile tubes, to spent AT4's, to inert bazooka rockets.
Link Posted: 2/22/2014 8:27:11 AM EST
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By rncbinc:
Yes we did, you gents had some interesting stories, I hope your friend has success in his new project. I will shoot you all an email when we get a range day set for the next machinegun shoot.
View Quote

Your sailboat story trumped mine
I'll keep you updated on the project.
This one looks like it will be fun too.
Link Posted: 2/23/2014 4:25:09 AM EST
[Last Edit: 2/23/2014 9:47:08 AM EST by rncbinc]
No doubt about that. I just ordered some material to turn out a prototype before I order the CNC parts. No point shelling out 2.5K for parts(5 sets) if you don't if the design works. The first one will differ only in that it fits into the bell in stead of replacing the bell. 3" 6061 aluminum round is much cheaper then 6" 6061 aluminum round. So by next week I will get into the shop and start the machining processes. I will also be testing the springs and other small pre-manufactured parts for serviceability. I will post photo's of the process for all those who are interested.
Link Posted: 2/23/2014 6:28:56 AM EST
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By rncbinc:
No doubt about that. I just ordered some material to turn out a prototype before I order the CNC parts. No point shelling out 2.5K for parts(5 sets) if you don't if the design works. The first one will differ only in that it fits into the bell in stead of replacing the bell. 3" 6160 aluminum round is much cheaper then 6" 6160 aluminum round. So by next week I will get into the shop and start the machining processes. I will also be testing the springs and other small pre-manufactured parts for serviceability. I will post photo's of the process for all those who are interested.
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Sounds good. Has the final design changed from the "inside the bell action" pictured in the CAD drawings towards the top of the page to something else?
Link Posted: 2/23/2014 9:51:42 AM EST
No changes to the final CNC plan, it will still be a total replacement of the rear bell with one that has the barrel nut threads and breech machined into it. I like the idea of not having to modify the existing rear bell so I can convert the tube back to a totally safe "wall hanger" with 3 screws.
Link Posted: 2/23/2014 4:28:12 PM EST
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By rncbinc:
No changes to the final CNC plan, it will still be a total replacement of the rear bell with one that has the barrel nut threads and breech machined into it. I like the idea of not having to modify the existing rear bell so I can convert the tube back to a totally safe "wall hanger" with 3 screws.
View Quote

Ahhhh, I see it now. Definately makes sense.
Link Posted: 2/26/2014 9:45:01 AM EST
Today I worked out the bolt face and bolt face detent that holds the round in place while outside the breach. I was going to use an AR15 9mm extractor but it did not fit in the plan...oh well, more spare parts for my tool box. The detent will be a small ball-nose spring plunger that threads into the bolt face. McMaster-Carr #3408A61. Most the springs will be from McMaster-Carr so finding a replacement if one breaks is easy.



Link Posted: 2/27/2014 12:13:53 PM EST
My prototype materials arrived today and I had a chance to get into the shop, stupid heat unit went out so it was a bit chilly(20 deg.) till my portable heaters kicked in. Anyway, I finished the lathe portion of the receiver bell. The hardest part was the threaded recess, if I were doing one again I would make the barrel threads forward of the bell end but since the is the prototype and the CNC guys will do all the hard work on the short run of parts I will leave it to print. Lots of good pics:





















Link Posted: 2/27/2014 12:16:07 PM EST
Tag for info and for being AGB's roommate and randomly running into this thread.
Link Posted: 2/27/2014 12:52:07 PM EST
Great progress!
Link Posted: 3/8/2014 4:54:08 AM EST
[Last Edit: 3/8/2014 5:03:53 AM EST by rncbinc]
I got a few parts made yesterday. These will be 2 of the 3 parts needed for the trigger bar that connects the firing mechanism on the AT4 to the trigger on the 9mm receiver. I am waiting on the bar stock to come in for the vertical piece and I am also waiting for the new firing pin and firing pin spring to come in. I opted for a pre-manufactured part in stead of designing my own. I chose one from a small pistol with similar design and shape as my original design idea. The cost is the same in the end but I don't have to worry about heat treating the part myself. I made 6 of each part so I would have some spares. I am probably over engineering the pieces but I want it to last. I just need to decide on weather or not I am going to use screws to assemble the parts or just hi-force silver solder. At 80,000 lbs. breaking force for the solder, I don't see them coming undone any time soon and all the pieces have a shoulder surface to take the horizontal load force. The last pic is a reference drawing with the trigger bar assembly in blue/black as it enters the receiver. It will have a return spring on the long portion and a pin through the bar providing a bearing surface for the spring. I was thinking I may need to reduce the size of the ends from 0.250 to 0.187 to provide more strength in the vertical transfer bar. Any thoughts from the mechanical engineers out there?





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