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Threading a .670 muzzle for 5/8-24


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Better late than never, I suppose. I'm photographically challenged but think I got one pic up/downloaded. I've ran 40 rounds through it and so far, so fantastic! I don't normally run a 7.62x39 and it'

Oops, sorry!  

I definitely went the bubba route. I used the Dinzag directions to remove and later re-install the fsb. After the fsb removal, I bolted a cross slide vise to a vertical board and put an angle grind

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  • 2 weeks later...

very informative - i've been itching to bring my .670" bbl diameter down for 5/8 x 24 -

i will now get an adjustable die and just thread it. tiny shoulder on my '09 muzzle.

i went another route for my FSB - but the old sleeve is still on, pending muzzle treatment -

++ on the FSC30 as i am in CA and no flash hiders "allowed" -

thanx for informing, esp. RED333 & way to DIY the cheek pad DrThunder88!

 

matt - w/pic for ideas/inspiration

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Edited by matt s
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Hey Matt,

 

Do you have a magazine lock on your rifle? If you do, you are completely allowed to have a flash hider. You only would not be able to have one if you had a semi-automatic centerfire rifle with a detachable magazine. I assume you do have one since you have a pistol grip. So if you want a flash hider, do it up! What part of NorCal do you live in?

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I definitely went the bubba route. I used the Dinzag directions to remove and later re-install the fsb. After the fsb removal, I bolted a cross slide vise to a vertical board and put an angle grinder in the vise. This allows the grinder to be lowered more "precisely". Then I routed a groove on a board and log to hold the barrel down. I screwed the board over the barrel tight, but where I could still rotate the barrel. I turned on the grinder and slowly lowered it while rotating the barrel, taking off a few thousands at a time till I got the diameter I needed for the die. Then I used an alignment tool (tat) from CSS to cut the threads. Somehow it worked and and I'm happy with it. I think I got lucky and would not recommend this route, but I had the longer barrel and could cut it down if it didn't work.

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Well, after a rough start, I got my .660 / .670 barrel threaded to 5/8 - 24. The M60 FH fits perfect and looks great.

 

photo2.jpg

 

photo1.jpg

 

A big thanks to everyone on this thread, especially those who answered my questions.

 

For anyone doing this for the first time, I can't emphasize enough how important it is to back out at least 2 or 3 times the distance every time you thread forward in order to break off the chips and clean out the threads. Also use lots of cutting fluid, I used Ballistol, and it worked great. Personally I didn't like threading the barrel in a horizontal position, and put the rifle butt on the floor and used some scrap lumber and screws to secure it to the side of my bench. This way I was able to keep it from moving (my little vice wasn't up to the task and my big vise is broken at the moment), was able to push down while I was getting it started, and the wood didn't scratch the rifle at all.

 

My threading tool came with a little built-in screw set into the gap and I turned it all the way in to adjust it to the biggest diameter it would go. I didn't have to tighten it for a second pass, the M60 FH went on fine.

 

She's almost done, just waiting on the scope, should be here tomorrow. I'll post pics soon.

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After reading this topic. I decided to thread my .670 barrel to 5/8-24. I used a 5/8-24 die with the TAT tool and screwed on the muzzle break on top of the TAT to make sure it was aligned. Everthing seamed good so i took off the TAT after 4 threads. I finished threading and put on the brake but noticed my muzzle brake was slightly slanting to one side. I think somewhere after the 4 threads something went wrong. I was wondering if anyone had the same problem and also if anyone knew how to fix this

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Well, after a rough start, I got my .660 / .670 barrel threaded to 5/8 - 24. The M60 FH fits perfect and looks great.

 

photo2.jpg

 

photo1.jpg

 

A big thanks to everyone on this thread, especially those who answered my questions.

 

For anyone doing this for the first time, I can't emphasize enough how important it is to back out at least 2 or 3 times the distance every time you thread forward in order to break off the chips and clean out the threads. Also use lots of cutting fluid, I used Ballistol, and it worked great. Personally I didn't like threading the barrel in a horizontal position, and put the rifle butt on the floor and used some scrap lumber and screws to secure it to the side of my bench. This way I was able to keep it from moving (my little vice wasn't up to the task and my big vise is broken at the moment), was able to push down while I was getting it started, and the wood didn't scratch the rifle at all.

 

My threading tool came with a little built-in screw set into the gap and I turned it all the way in to adjust it to the biggest diameter it would go. I didn't have to tighten it for a second pass, the M60 FH went on fine.

 

She's almost done, just waiting on the scope, should be here tomorrow. I'll post pics soon.

 

So in conclusion would you say threading a .670 barrel to 5/8x24 without trimming down barrel is easily done or risky business?

 

Before i try. I was wondering if it was possible to rethread threads? If not i guess im going to have to move back my front sight block forward again and go with the SGM clamp on muzzle brake route. Im sure that would fix the problem. Too bad they didnt make a 74 style clamp on brake

 

If your not able to correct it i just so happen to have a new SGM TACTICAL Bolt on brake for sale, $100 shipped or we might even be able to work out a deal on those threading tools if your interested032.gif

Edited by THE VILLAIN
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Hey Matt,

 

Do you have a magazine lock on your rifle? If you do, you are completely allowed to have a flash hider. You only would not be able to have one if you had a semi-automatic centerfire rifle with a detachable magazine. I assume you do have one since you have a pistol grip. So if you want a flash hider, do it up! What part of NorCal do you live in?

 

Yes - mag lock installed - new picture isn't close-up, but you can see the shroud bolted onto the bottom of the trigger guard.

your info makes this thread even happier for me - thanx.

I live in Amador County, kinda on the way to Tahoe. Looks like you are up in the beautiful NW corner. i worked there for some time and really loved it. Go Lazlo.

 

Sorry I can't figure out how to quote - matt

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Edited by matt s
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  • 4 weeks later...

So in conclusion would you say threading a .670 barrel to 5/8x24 without trimming down barrel is easily done or risky business?

 

I'm wondering the same thing...?

Don't really want to thread my barrel for 17x1 and have to bore my FH out and tap that for 17x1. I'd much prefer to thread my .670 barrel for 5/8-24 and be done with it.

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What I discovered is if you have the older style 0.670 bbl with the taper at the muzzle and the "cap" on the sight (which covers the taper), then you can thread to 5/8 x 24 without turning the bbl down. If you have the new style with the straight bbl and front sight that goes all the way to the end - don't try it!!!nonono.gif I did and only ended up dulling the teeth on the die and making a shiny, making it useless! I also just made a shiny ring on the muzzle. I ordered a bbl trim kit from Dinzag and it was on my doorstep 3 days later (thanks Brian!) I also had to get a new die. Ah well an expensive lesson learned! Would have been cheaper to go the gunsmith route!

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  • 2 weeks later...

OK so I gave this a try...threading my own .670 barrel for 5/8-24. Got all the goods from CNC Warrior including cutting fluid. Everything was going great until about 5 threads in (after the taper)...I started to encounter a lot of resistance because of the increase in material to cut and eventually my die chipped apart and became pretty much useless. The good news is I got about 5 or 6 solid threads in and my FH goes on nicely and I'm going to have it tack welded in place.

 

Because my barrel currently has about half the threads (half the thread depth/length along the barrel) that the flashhider itself has, the flashhider can't screw all the way on it's full depth of threads. So there is space between the ID "entrance" of the FH and the crown of the barrel, approximately 1/4" (another 1/4" the FH could screw onto the barrel if I had more threads on it). Could this cause any negative affects, like say on accuracy? I'd think if my barrel is crowned well (it will be when my Dinzag tools show up) and the threads on the gun are straight then whatever happens in the space would be uniform and then not affect accuracy noticeably.

Edited by ColoradoKLR650
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I take that ^ back, my die didn't completely fall apart on my first attempt. Althought I thought it was toast I gave it another try today with extra fluid and got a extra five threads for about 10 or 11 threads total! I was so stoked and could have kept going...I wasn't encountering the sort of resistance that broke the die my first attempt. I think I just didn't clean the chips away often enough or use enough fluid that first attempt so eventually the resistance made my effort turn to breaking the die instead of cutting away barrel material. This time I simply used to compressed air to blow the chips away after every 3 or so cuts forward then added more fluid. What a difference! I'd say more was more in this case.

 

So to anyone thinking about attempting to thread their .67x barrel for 5/8x24 themselves, I'd say give it a shot. I'm a straight bubba and I did it! According to the micrometer I have access to at work, my barrel past the taper was actually .678! I measured it like 6 or 7 times and reset the zero on it a few of those times as well. Then again I could still believe that this was inaccurate and my barrel isn't quite that close to .68 but seeing that was surprising none the less. Pics are forthcoming.

Edited by ColoradoKLR650
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I take that ^ back, my die didn't completely fall apart on my first attempt. Althought I thought it was toast I gave it another try today with extra fluid and got a extra five threads for about 10 or 11 threads total! I was so stoked and could have kept going...I wasn't encountering the sort of resistance that broke the die my first attempt. I think I just didn't clean the chips away often enough or use enough fluid that first attempt so eventually the resistance made my effort turn to breaking the die instead of cutting away barrel material. This time I simply used to compressed air to blow the chips away after every 3 or so cuts forward then added more fluid. What a difference! I'd say more was more in this case.

 

So to anyone thinking about attempting to thread their .67x barrel for 5/8x24 themselves, I'd say give it a shot. I'm a straight bubba and I did it! According to the micrometer I have access to at work, my barrel past the taper was actually .678! I measured it like 6 or 7 times and reset the zero on it a few of those times as well. Then again I could still believe that this was inaccurate and my barrel isn't quite that close to .68 but seeing that was surprising none the less. Pics are forthcoming.

 

Good job! What break are you going with?

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I went with an AAC Blackout Flash-hider. I'm sort of a prepper and believe that a FH is more tactically sound than a muzzle brake given many tactical realities (for example: ambushes are best at night...most firefights occur within 100 yards [i.e. long range accuracy isn't quite that important in that situation])...and the Blackout got the best reviews even in directly comparisons (with the Smith Vortex, A2 birdcage, etc.). I'm still considering a brake and am stuck between an AAC Blackout muzzle brake or AAC Breakout but I can't find any info on the differences between the two...both are suppose to be muzzle breaks but I think one or both is a compromise between FH and brake. I'm still also considering a FSC30 or PRC from PWS.

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Also, I'd add that during my threading procedure I never once let off on the adjustment screw of the die. In other words, I kept the die adjusted to it's max diameter the entire time...it barely fit in the die holder, I had to tap it in with a small hammer. This also meant that my TAT was never actually held stationary in the die, it spun freely the whole time. I saw no disadvantage to that and it worked out for me in the end. I also kept the barrel end of the TAT oiled well because I didn't want it fouling up the rifling or crown.

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I agree the FSB was a B to remove. After I removed the pins with a drill press, it wouldn't even budge in any direction. I ended up cutting it with a dremel length-wise along the bottom, being sure to avoid cutting into the barrel. Then I was able to remove it by expanding it with a flathead screwdriver. With how far back my FSB needed to be re-located for my FH, I couldn't even re-use the second pin cut-out. And frankly, I didn't feel like dealing with pins anymore...so I just put the FSB in position and had a guy put a tack weld on both ends of the bottom side of my FSB where the cut is. It looks bubba, no doubt, but with my new paint job it's hardly noticeable other than that my FSB has no pins in it. I may still put one pin in just to make sure it doesn't go flying if both of the welds give but I'm not too worried about it.

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