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Posted: 1/8/2023 4:46:14 PM EDT
So I have plenty of 5.56's and decided to see if I could turn mine into a 300 blackout.
 Handguard was easy, 2 torx screws.  The long barrel nut was kind of strange, but I kept going. The gas black is set in place with 2 roll pins that came out easy.  Trigger pin for size comparison.  Also the barrel was milled very differently than any ar-15 barrel I have ever seen. Here is some of the strange milling.  Never seen a gas block with a hole on the top.  The gas block was on so tight I had to remove the barrel nut and gas tube first, then had to hammer the it off with a gunsmith hammer.     Everything seemed to be going smoothly until I went to install the barrel nut. Apparently since they went with an unusual gas block setup they didn't need the barrel nut to have a normal inside diameter, so they didn't. The inside diameter is barely larger than .750. So now I'm stuck with some decisions.   So here is my problem, I was going to buy a new barrel nut that would fit over the barrel and inside the handguard, but I can't find one, The outside diameter is 1 5/16" and most companies don't list there barrel nut OD. And it's definitely not a standard size. My only other options are mill the barrel down or mill the inside of the nut I have. Some pics of receiver    
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Posted: 1/8/2023 4:55:44 PM EDT
[#1]
Think you shoulda picked a different gun for this project
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Posted: 1/8/2023 5:06:17 PM EDT
[#2]
I can always put it back together, I was just curious if it could be done.
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Posted: 1/8/2023 5:09:12 PM EDT
[#3]
Call the original manufacturer and see if they offer barrels in the caliber you want.
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Posted: 1/8/2023 5:17:25 PM EDT
[#4]
They don't and I have been in contact with them.
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Posted: 1/8/2023 5:23:11 PM EDT
[#5]
Quote HistoryQuoted: They don't and I have been in contact with them. Can you find a barrel company willing to re-chamber, drill out and re-rifle the original barrel? |
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Posted: 1/8/2023 5:30:24 PM EDT
[#6]
That seems like a lot of work and money when I can just mill down a hump on the barrel I have.
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Posted: 1/13/2023 12:49:59 PM EDT
[#7]
Even if you could buy a spare FM barrel nut, you can’t bore it out any more than those two, giant “o-ring groove” depths allow. Turning the blackout barrel to match the FM barrel profile forward of the barrel extension is an easy operation if you have access to a lathe. Not sure if you need to do that before milling those flats into the taper, maybe not. Plenty of cheap blackout barrels to try that on.
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Posted: 1/13/2023 11:48:24 PM EDT
[#8]
Their barrels use a taper lock system on the barrel nut. Heres a few videos under the hood/video on features/improvements they tried to make.
 The NEW GEN 2 MIKE15 (How it works) Next video is long but super informative  Failed To Load Title |
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Posted: 1/14/2023 3:58:51 PM EDT
[#9]
Does the taper on the 300 barrel match the original barrel?
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Posted: 1/14/2023 5:36:05 PM EDT
[#10]
almost certainly not
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Posted: 1/14/2023 7:02:53 PM EDT
[#11]
Geez this disassembly process almost makes me want to buy one. Looks like some heavy duty stuff
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Posted: 1/15/2023 12:52:46 AM EDT
[#12]
That's what I thought too. I am impressed by it
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Posted: 1/15/2023 4:27:38 AM EDT
[#13]
You could just call the company and ask their engineers. I mean you've totally blown your warranty, hell they might find it interesting and help.
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Posted: 2/4/2023 3:41:24 PM EDT
[#14]
Hopefully, they'll offer the 9" pistol in 300BLK.
Otherwise, I'm tempted to buy the 223 version and have a barrel made. Would make a nifty SBR with a SIG folding & telescoping stock, and be shorter, lighter, and less expensive than an MCX. Hope this stays out of archive. |
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Posted: 4/2/2023 2:14:30 PM EDT
[#15]
BTT.
Going to check about a custom barrel. |
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Posted: 4/4/2023 10:29:35 PM EDT
[#16]
This is easier then you think. I have done a few with 7.5 inch barrels and one with a 5 inch barrel in 7.62x39. You just need to machine down the diameter of the gas block shoulder on the barrel, I just used my bench grinder just rolled the barrel in the opposite direction of the grinding wheel for a few minutes. This works really well, then the barrel will pass right through the barrel nut. If your doing a rifle length build no need to cut the handguard. If doing a pistol lenth build the 11.5 inch uppers handguard can be cut down enough to run a 8 inch barrel and put a suppressor on it to do a 7.5 in barrel the 9 inch uppers handguard can be cut down. I am not a gunsmith jus/a firearm enthusiast that taught myself how to do all my own work. I am doing another This weekend for a friend. Here's Pick of my 7.5 inch 7.62x39 foxtrot mike upper.
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Posted: 4/11/2023 9:17:54 PM EDT
[#17]
Quote HistoryQuoted: This is easier then you think. I have done a few with 7.5 inch barrels and one with a 5 inch barrel in 7.62x39. You just need to machine down the diameter of the gas block shoulder on the barrel, I just used my bench grinder just rolled the barrel in the opposite direction of the grinding wheel for a few minutes. This works really well, then the barrel will pass right through the barrel nut. If your doing a rifle length build no need to cut the handguard. If doing a pistol lenth build the 11.5 inch uppers handguard can be cut down enough to run a 8 inch barrel and put a suppressor on it to do a 7.5 in barrel the 9 inch uppers handguard can be cut down. I am not a gunsmith jus/a firearm enthusiast that taught myself how to do all my own work. I am doing another This weekend for a friend. Here's Pick of my 7.5 inch 7.62x39 foxtrot mike upper.https://photos.app.goo.gl/h9ckPieJZzt1umwW6  Attached File |
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Posted: 4/15/2023 10:32:06 AM EDT
[#18]
Quote HistoryQuoted: This is easier then you think. I have done a few with 7.5 inch barrels and one with a 5 inch barrel in 7.62x39. You just need to machine down the diameter of the gas block shoulder on the barrel, I just used my bench grinder just rolled the barrel in the opposite direction of the grinding wheel for a few minutes. This works really well, then the barrel will pass right through the barrel nut. If your doing a rifle length build no need to cut the handguard. If doing a pistol lenth build the 11.5 inch uppers handguard can be cut down enough to run a 8 inch barrel and put a suppressor on it to do a 7.5 in barrel the 9 inch uppers handguard can be cut down. I am not a gunsmith jus/a firearm enthusiast that taught myself how to do all my own work. I am doing another This weekend for a friend. Here's Pick of my 7.5 inch 7.62x39 foxtrot mike upper.https://photos.app.goo.gl/h9ckPieJZzt1umwW6 What about the taper at the chamber end? Also, what gas blocks have you used? |
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Posted: 4/15/2023 6:22:35 PM EDT
[#19]
Quote HistoryQuoted: This is easier then you think. I have done a few with 7.5 inch barrels and one with a 5 inch barrel in 7.62x39. You just need to machine down the diameter of the gas block shoulder on the barrel, I just used my bench grinder just rolled the barrel in the opposite direction of the grinding wheel for a few minutes. This works really well, then the barrel will pass right through the barrel nut. If your doing a rifle length build no need to cut the handguard. If doing a pistol lenth build the 11.5 inch uppers handguard can be cut down enough to run a 8 inch barrel and put a suppressor on it to do a 7.5 in barrel the 9 inch uppers handguard can be cut down. I am not a gunsmith jus/a firearm enthusiast that taught myself how to do all my own work. I am doing another This weekend for a friend. Here's Pick of my 7.5 inch 7.62x39 foxtrot mike upper.https://photos.app.goo.gl/h9ckPieJZzt1umwW6 @snaketac Question 1: Would a different (ie pencil) barrel profile be better or worse than the standard Gvt profile barrels you’re reprofiling? Question 2: I’m assuming you swapped the bolt out to run 7.62x39, could you do say…5.45 and use the new Mike 102 lowers for a 5.45 AR that uses -74 mags? Probably with mods to lower if some sort but doable? Question 3: with a light tough and dremel, how doable would this be? To do the barrel reprofiling for say .300BO? |
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Posted: 4/21/2023 6:44:35 PM EDT
[#20]
Quote HistoryQuoted: What about the taper at the chamber end? Also, what gas blocks have you used? The taper on the barrel nut I assume is what you mean and that's! non-issue, it still tightens down like a standard barrel nut on a regular barrel. As for gas blocks I've used a few different micro blocks that attach with set screws. If you go with an adjustable one just make sure it's no taller than a standard micro gas block so it doesn't interfere with the op rod. |
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Posted: 4/21/2023 7:00:42 PM EDT
[#21]
Quote HistoryQuoted: @snaketac Question 1: Would a different (ie pencil) barrel profile be better or worse than the standard Gvt profile barrels you’re reprofiling? Question 2: I’m assuming you swapped the bolt out to run 7.62x39, could you do say…5.45 and use the new Mike 102 lowers for a 5.45 AR that uses -74 mags? Probably with mods to lower if some sort but doable? Question 3: with a light tough and dremel, how doable would this be? To do the barrel reprofiling for say .300BO? 1. I don't think a pencil barrel would make any difference, from what I've seen all barrels have to high of a shoulder behind the gas block. 2. If 5.45 bolt fits in a standard AR15 carrier it will fit in the FM carrier. I don't now about the mike 102 lowers, I thought about buying one to see if I could get it to take standard AK mags , but I'm gonna just wait for their 7.62 3. A 300BO would be just as easy as any other barrel. I was going to do that next but I built a rattler instead. Good luck with your project. Tim... |
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Posted: 4/30/2023 9:46:16 PM EDT
[#22]
Quote HistoryQuoted: The taper on the barrel nut I assume is what you mean and that's! non-issue, it still tightens down like a standard barrel nut on a regular barrel. As for gas blocks I've used a few different micro blocks that attach with set screws. If you go with an adjustable one just make sure it's no taller than a standard micro gas block so it doesn't interfere with the op rod. Does this mean it tightens down on the collar, not just the taper if it's smaller? |
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Posted: 5/1/2023 7:14:15 AM EDT
[#23]
Quote HistoryQuoted: Does this mean it tightens down on the collar, not just the taper if it's smaller? Yes, exactly!! |
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Posted: 5/2/2023 8:24:24 PM EDT
[#24]
Quote HistoryQuoted: Yes, exactly!! Quote HistoryQuoted: Quoted: Does this mean it tightens down on the collar, not just the taper if it's smaller? Yes, exactly!! Awesome! This makes things SO much easier... Thanks! |
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Posted: 5/15/2023 9:00:17 PM EDT
[#25]
I see different charging handle locations on the same length uppers.
The idea of a 7.5" 300 BLK is very appealing. |
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Posted: 5/16/2023 7:27:41 AM EDT
[#26]
If you start with the 9" upper you can cut the handguard short enough to run a 6.5" 300BO barrel.
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Posted: 5/16/2023 8:17:41 PM EDT
[#27]
Quote HistoryQuoted: If you start with the 9" upper you can cut the handguard short enough to run a 6.5" 300BO barrel. My OCD wouldn't tolerate any cuts into slots. Already have 6" and 8" 300 BLK SBRs. The folding stock on a FM-15 would be the big advantage for fitting in a bag. I figure 9" with folder would be real close to my 6" PDW. The new ammo from SIG should be pretty good in a 7.5" as it was designed for 6.75". Someday... ETA: I see it now! The fixed gas 9" slots line up... Thanks! |
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Posted: 7/30/2023 11:41:42 AM EDT
[#28]
BTT
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