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Posted: 3/19/2021 5:28:05 PM EDT
I'm putting this build article in A2 Builds because my upper receiver is an AR15/M16 upper. It's really just a proof of concept project. It will have a modified Ruger Mini 14 long stroke gas system with an FN SCAR style cocking lever. I'm not sure whether or not this will all work out but I'm going to give it a try. Here a pic of my AR15 bolt carrier [my bolt parts have arrived yet], the Mini 14 gas piston, and the Mini 14 recoil spring. I got the gas piston and recoil spring from Numrich Arms and they're supposed to be genuine Ruger parts.
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Posted: 3/19/2021 5:32:12 PM EDT
[#1]
AR Stoner Heavy 16" Carbine Barrel
Here's a pic of my heavy AR Stoner 16" carbine barrel with a 1/7" twist. 
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Posted: 3/19/2021 5:36:31 PM EDT
[#2]
Here's my M16A2 upper receiver which will be used on this project.
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Posted: 3/19/2021 5:42:52 PM EDT
[#3]
Here are some pix of a BRN-180 lowers. I'll be using this from my lower. I've got on back order a BRN180 upper assembly but there's no ETA for them. That was why I decided to launch this project. The BRN180 is a Brownells project which uses an upper similar to an AR180. The AR180 had a short stroke gas system and a folding stock.
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Posted: 3/19/2021 7:16:06 PM EDT
[#4]
Subbed.
In for updates. I like where this is going |
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Posted: 3/19/2021 8:34:15 PM EDT
[#5]
This is a pic of the FN SCAR's charging handle. It's mounted on the rifle on the forearm just under the Picatinny rail. It's ambidextrous and can be mounted for either right handed and left handed shooters. On the FN SCAR it attaches directly to the bolt carrier. Mine will attached directly to the operating rod in a similar position and also be ambidextrous. This design is vastly superior to the charging handle on the M16/AR15 which IMHO has one of the most poorly designed charging handles ever put on a rifle!
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Posted: 3/19/2021 9:04:27 PM EDT
[#6]
Here's a BRN180 set up as an SBR, I think. It's got a folding stock and is set up with an AR15 lower. The BRN180 upper assembly can be set up either on an AR15 lower or a BRN180 lower.
Photo courtesy Recoilweb 
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Posted: 3/20/2021 9:20:32 AM EDT
[#7]
That thing looks pretty cool.^^^
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Posted: 3/20/2021 9:41:43 AM EDT
[#8]
Ost
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Posted: 3/20/2021 12:13:24 PM EDT
[#9]
My bolt carrier, an AR15 unit I bought off of GunBroker. I've got to saw it in two and machine off the back end. For those of you not familiar with the AR180 series it used a rectangular shortened bolt carrier and it had the cam pin rotated off to the left side.
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Posted: 3/20/2021 12:50:48 PM EDT
[#10]
Just off the UPS truck! My 304L stainless steel .750"x12 bar stock from OnLine Metals. This will be the rifle's operating rod. I've got to machine it down and drill holes in both ends for the recoil spring relief and for the gas piston on the other end. It'll attached to the top of the bolt carrier.
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Posted: 3/20/2021 1:47:48 PM EDT
[#11]
Tag!
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Posted: 3/20/2021 5:19:13 PM EDT
[#12]
Here I've sawed the suitcase handle off the top of my A2 Upper. I'm going to make it into an A4 [sort of]. In the second pic I've got it set up in the mill. The job was harder than I thought it would be. The pin bosses were almost wider then my vice jaws so the setup wasn't very rigid and kept wanting to move on me after I started the milling. However I finally got 'er done! The third pic shows the completed job.
  
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Posted: 3/20/2021 9:07:56 PM EDT
[#13]
More Mill Work
Here I'm opening up the hole for my operating rod. This was a more difficult setup then when I milled off the top of the receiver. My operating rod is going to be square like the one on the FN SCAR. So I had to bore out the X shaped hole for the gas tube in the front of the receiver and then I've got to open up the hole further with square files. I could have probably opened it up more with the 5/16 end mill but I didn't trust myself not to go too far into the walls. 
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Posted: 3/20/2021 9:33:47 PM EDT
[#14]
Opening up rectangular hole
Here I'm opening up the rectangular hole with my square files. This will give you an idea. This is slow and tedious work! I'm worried because of the narrow dimensions in the top of the receiver there isn't going to be much wall thickness when I drill out my holes for the recoil spring and the gas piston relief. This was also why I selected the Ruger Mini 14 recoil spring and it's gas piston. Both are around .375" OD. 
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Posted: 3/20/2021 9:42:53 PM EDT
[#15]
OST!
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Posted: 3/21/2021 6:11:42 AM EDT
[#16]
Quote HistoryQuoted: Here I've sawed the suitcase handle off the top of my A2 Upper. I'm going to make it into an A4 [sort of]. In the second pic I've got it set up in the mill. The job was harder than I thought it would be. The pin bosses were almost wider then my vice jaws so the setup wasn't very rigid and kept wanting to move on me after I started the milling. However I finally got 'er done! The third pic shows the completed job. https://i.imgur.com/3Efh9w1.jpg https://i.imgur.com/wjfFji3.jpg https://i.imgur.com/uX32RIu.jpg |
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Posted: 3/21/2021 7:54:35 AM EDT
[#17]
You put this in the A2 forum and the chop off the carry handle?
Please move this to the piston forum! |
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Posted: 3/21/2021 10:15:48 AM EDT
[#18]
OP, you do realize there are two bolt carriers on the market that locate the recoil springs in the receiver, correct?
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Posted: 3/21/2021 6:42:14 PM EDT
[#19]
BackBencher Posted: "OP, you do realize there are two bolt carriers on the market that locate the recoil springs in the receiver, correct?"
No, I didn't! Who are they? I wasn't trying to reinvent the wheel here. |
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Posted: 3/21/2021 10:36:42 PM EDT
[#20]
Will have to look em up. And there are drop in short stroke pistons as well, some that use bolt on bolt bosses instead of the gas key.
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Posted: 3/22/2021 12:23:27 AM EDT
[#21]
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Posted: 3/22/2021 12:24:36 AM EDT
[#22]
Tag... |
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Posted: 3/22/2021 5:20:35 AM EDT
[#23]
I looked up the Evolution Weapon Systems with a Google search. Looks like they've got a pretty neat product. However it uses the regular AR15 gas impingement system which I was trying to avoid because I have some issues with it. My project rifle will have a modified long stroke Ruger Mini 14 gas system with a FN SCAR style cocking lever. I'm still working on my rectangular hole in the front of the receiver for the operating rod. It's slow going because I'm having to do it by hand with a square file.
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Posted: 3/22/2021 8:07:46 AM EDT
[#24]
There are some short stroke gas piston systems that drop in, at least one of which just replaces the gas key. One is perhaps longer stroke than the others, as it claims to be a long stroke piston.
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Posted: 3/22/2021 1:57:27 PM EDT
[#25]
Good luck with the project, and thanks for sharing pics. I've wanted to build something similar, but haven't gotten around to it.
The ZM Weapons LR-300 was similar, but with an extended gas key and recoil spring above the barrel if i understand correctly. |
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Posted: 3/22/2021 3:40:16 PM EDT
[#26]
AR15/M16 Bolt Parts Arrive
Just got my AR15/M16 bolt parts from Midway USA. These included the bolt, firing pin, cotter pin, and the cam pin. Everything fit together perfectly and it rotates in and out of battery. I've still got to whack off the rear end of the bolt carrier. If you look carefully you can see a shiny spot just behind the cotter pin hole where I attempted to saw the carrier in two. This was an utter failure and so was my hack saw! I should have known better. I'll have to whack it off with my die grinder and a cut off wheel. And then I'll have to machine off the back end square with a carbide mill cutter. 
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Posted: 3/23/2021 11:47:01 AM EDT
[#27]
Or...you could have bought this.
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Posted: 3/23/2021 4:14:05 PM EDT
[#28]
Acetal Rod
Just got this from MSC, a 1"x48" acetal rod. I need it to make a buffer for the lower receiver. I was hoping to get delrin and this is the closest thing to delrin I could find. It seems to be too hard, I think. There's a .375"x .250" deep flat bottomed hole at the back of my lower receiver. I'm pretty sure the Brownells engineers put it there for relief for the rear of the firing pin when the sawed off bolt carrier bottoms out. I plan to make it a .250" thick as a buffer with a relief for the firing pin. If it's too hard it will shatter. But the material also needs to be machinable which I'm pretty sure this is. Not all polymers machine well. Also included in my shipment was my 1/4" carbide end mills which I need to machine off the back of my bolt carrier and also put the driver pocket in the top of the bolt carrier.  " />
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Posted: 3/23/2021 4:24:29 PM EDT
[#29]
[color=#0000ff]Dex223 Posted:Or...you could have bought this and a link to the LR300 bolt carrier sold by Gun Parts Corp [Numrich Arms].[/color]
I would have had I known it to be available before I ordered my AR15 bolt carrier. I had to look up the LR300. I noted it has a folding stock hence the need for the shortened [non AR15/M16 type bolt carrier] bolt carrier. But if I had bought it I'd still have to machine off a good portion of the back end. I'm worried about getting enough bolt carrier travel in the receiver. It will be shortened by about .250" by the buffer at the back of the receiver. |
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Posted: 3/24/2021 8:04:34 PM EDT
[#30]
Rectangular Hole Completed
I finally got my rectangular hole in the front of the upper receiver finished. This was a real tedious and time consuming job! Next op is to bob the rear of my bolt carrier and then I have to machine it off square and then machine the driver slot in the rear on the top. 
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Posted: 3/24/2021 8:29:44 PM EDT
[#31]
Bolt Carrier Key Dismounted
I've dismounted my bolt carrier key since it won't be needed in the new prototype. Fortunately the screws weren't staked down at the factory. The carrier key on an AR15/M16 is what keeps the bolt carrier aligned at 1200 and keeps it from rotating. I'll be putting in a new driver slot where the carrier key used to be and the operating rod will have a boss sticking down to engage it. And it will keep the bolt carrier aligned during firing. 
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Posted: 3/24/2021 8:36:04 PM EDT
[#32]
Following
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Posted: 3/24/2021 9:19:15 PM EDT
[#33]
OST
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Posted: 3/24/2021 10:46:03 PM EDT
[#34]
Bolt Carrier Work
The first pic is my Dotco die grinder. It's air powered not electric and it's got a .0625x4.00" cutoff wheel. In the second pic I'm cutting the bolt carrier in two. It didn't take long at all!  
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Posted: 3/24/2021 11:20:57 PM EDT
[#35]
Quote HistoryQuoted: Acetal Rod Just got this from MSC, a 1"x48" acetal rod. I need it to make a buffer for the lower receiver. I was hoping to get delrin and this is the closest thing to delrin I could find. It seems to be too hard, I think. There's a .375"x .250" deep flat bottomed hole at the back of my lower receiver. I'm pretty sure the Brownells engineers put it there for relief for the rear of the firing pin when the sawed off bolt carrier bottoms out. I plan to make it a .250" thick as a buffer with a relief for the firing pin. If it's too hard it will shatter. But the material also needs to be machinable which I'm pretty sure this is. Not all polymers machine well. Also included in my shipment was my 1/4" carbide end mills which I need to machine off the back of my bolt carrier and also put the driver pocket in the top of the bolt carrier. https://i.imgur.com/FwUPMuz.jpg" target="_blank">https://i.imgur.com/FwUPMuz.jpg For Delrin, you can go to McMaster-Carr, and if you only need a small amount, can get 1' lengths. McMaster-Carr |
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Posted: 3/24/2021 11:29:50 PM EDT
[#36]
More Bolt Carrier Work
In the next pic I've just bobbed the bolt carrier in two. In the next pic I've got the front half of the carrier set up in my Index mill in my V-block getting the back end machined flat.  
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Posted: 3/25/2021 7:37:08 AM EDT
[#37]
Dex223 sent me a link to McMaster-Carr to a page with Delrin-Acetal 1" rods. The add stated that they were poor at impact resistance. This is the problem with my acetal rod I got from MSC. I'm pretty sure it will saw, drill and turn well but it's impact resistance is questionable. One of the guys on 1911 Forum sent me a link to a Urethane site. I think this is what I probably need. It's more like the buffer mattrial on the AR15/M16 buffer, I think. However I may have trouble machining it. Fortunately the buffer I've designed for my project will be easy to swap out.
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Posted: 3/25/2021 8:06:19 AM EDT
[#38]
Cool Stuff !
Like the 'outside the box' builds. |
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Posted: 3/27/2021 4:28:31 AM EDT
[#39]
Back of the Bolt Carrier Machined Off
Here I've machined off the back of the bolt carrier flat. I wonder if it's now too short or not. The bolt needs some mass to effectively strip the cartridges out of the magazine. However I'm making a new operating rod which will add some mass to the system. Next step is to machine the driver keyway in the top of the carrier. 
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Posted: 3/27/2021 6:27:47 AM EDT
[#40]
On Machining the Driver Keyway
I'm now working on my driver keyway in the top of the bolt carrier. The driver will be machined into the bottom of my 304L stainless operating rod. According to my scientific calculations [done with a Mitutoyo 6" dial caliper] an AR15/M16 carrier key is approximately .408" wide. The carrier key slot in the top of the A2 Upper is approximately .418" wide giving .010" of slop between the two. So now I have to decide how wide and how long to make my driver keyway. I'm using the same .250" carbide cutter to cut the keyway as I used to machine off the back end of the carrier. |
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Posted: 3/27/2021 6:37:54 AM EDT
[#41]
OST
Cool project! |
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Posted: 3/27/2021 9:55:41 AM EDT
[#42]
OP, on the subject of BCG mass, the severely undergassed 27" bbl rifle I built runs fine w/ no weights in the buffer and a lightweight steel carrier. While tuning it, I had noticeably better feeding from a curved Magpul mag vs a straight Magpul 20 rnder.
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Posted: 3/27/2021 9:28:03 PM EDT
[#43]
Backbencher wrote: OP, on the subject of BCG mass, the severely undergassed 27" bbl rifle I built runs fine w/ no weights in the buffer and a lightweight steel carrier.
Gas volume was another question I had. I noticed my gas vent hole on my AR Stoner carbine barrel only had about a 1/16" [.0625"] hole. I can't recall what the size on my M1A or LR308 was. I know they were bigger the .0625". Since I'm doing away with the direct impingement gas system and going to a modified long stroke Ruger Mini 14 gas piston system I was wondering if I'll need to open up the vent hole. Fortunately I can always do that later if it needs to be done. Here I've finished cutting the driver keyway. I decided to make a .416" slot. Those are the .416" gage blocks inserted into the keyway. In the second pic you can see how I've cut out the driver keyway. I made the surfaces flat so I didn't have to round off the ends of the driver. I went down .175" from the flat under the carrier key. I almost broke thru so on the next one I'll only go down .150".  
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Posted: 3/28/2021 6:56:37 AM EDT
[#44]
More on Gas Port Size
I just checked out my Ruger Mini 14 Gas Piston Pipe and Gas Port Bushing. Both have what looks to be [not a scientific measurement] 3/32" [.0937"]] vent holes. I have yet to strip down my Mini 14's gas block to see what sized vent hole it has on it's barrel. Later I'll check out the vent holes in Piston Pipe and Gas Bushing with Number Drills to get a better idea as to what the actual hole diameters are. 
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Posted: 3/28/2021 7:07:44 AM EDT
[#45]
Modified Bolt Carrier Reassembled
I've reassembled the bolt carrier with it's AR15/M15 parts. If you look carefully you can see on the forward construction slot where the cutter almost broke thru into the bolt relief! 
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Posted: 6/1/2021 10:05:20 PM EDT
[#46]
Ready to see more.
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Posted: 6/2/2021 1:55:22 AM EDT
[#47]
This is coming along nicely. Good shit OP
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