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Threading a .670 muzzle for 5/8-24


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I finally knocked my .308's FSB off and found that I have a 0.670" diameter underneath it. I've read Dinzag's tutorial on the subject, which says:

...0.630” lends itself to being threaded for 5/8-24 threads and 0.670” lends itself to being threaded for 17x1 threads.

 

But, if you'll excuse what reads like a child's temper tantrum, I don't want 17x1mm muzzle threads. I want a Battlecomp like Jim Digriz. I'd at least prefer the option to use any of the many, varied muzzle devices made for the 5/8-24 threads.

 

So here's the question, is the conventional wisdom that a 0.670" muzzle cannot be threaded in 5/8-24 just a guideline, or is it a sure thing that I'm going to screw something up if I try it?

 

I don't have access to a lathe, nor can I be arsed to hire the job out to a gunsmith. Paying for shop time to remove two hundredths of an inch from the barrel's radius just seems profane. If 0.670" is fatally wide, can I draw file some shallow flats on the muzzle, gradually connecting them to form a polygonal profile roughly approximating a circle of the correct diameter? I envision draw filing at 12 o'clock, 6 o'clock, 9 o'clock, and 6 o'clock before rotating the barrel 45 degrees and continuing the same pattern. If I use the same number of strokes each time, I imagine the end result will be close enough to circular that the die, indexed to the barrel via TAT, will round off the vertices.

Edited by DrThunder88
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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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The engineer in me says to get it done on a lathe, your taking off .040 of material and it needs to be straight. How ever I do wonder if you did do the file routine and then used the thread alignment tool, might work. The other consideration is the cost of making a mistake and either having to cut the barrel down or replace it, really out weighs the cost of getting done on the lathe in the first place.

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Dinzag also has bbl trimmers that you chuck in a hand drill for turning down the bbl under his tools section. To get everything you need (it's 3 parts) costs ~$140. Too bad he doesn't rent the tools anymore b/c this is what I wanted to do. I couldn't justify spending the extra $140 since I already dropped ~$70 on the threading tools for a one time job. I ended up installing his AK74 style break that he reams to 17x1 and couldn't be happier. It cuts way down on recoil, but does seem to increase the flash - which I didn't think possible big_smile.gif He does also offer a phantom hider reamed to 17x1, but I was more concerned w/ recoil reduction.

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Cool. Thanks for the replies so far! Mine's an '08, so the transition point may be in there somewhere.

 

I got the FSB boxed up and ready to be shipped to Dinzag for reaming, so one way or another I'm going to get this thing threaded! It's funny, now I kind of like the look of the rifle with the plain, unadorned muzzle end.

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Alright, mine is a 09 and is .670.

I did get it threaded 5/8 x 24, it was tough, but did some reading

and have some training in a machine shop work.

Used cutting oil and the threads came out fine.

I picked up my die from CNC worrier, it is an adjustable die and

I opended it up a bit and it started fine.

Did not have to recut smaller, my brake fit great.

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Informative thread. I too am going to add a brake and since my 308 is an 09 suspect it is .670. I don't want the expense of buying a barrel trimmer but do want to go 5/8 24 because that's what the brake I want is threaded for. I was originally going to use a JP Eliminator but am not sure if I'm secure enough in my manhood to handle the ridicule I'd get from everyone who saw it. Currently I'm leaning toward their "Large Profile" Tactical Compensator. It's supposed to be as effective as the Eliminator but with more conventional looks. There's a neat video on their website showing the Eliminator being fired one handed on a full auto M16. Yes, it's just a 5.56 but 30 rounds of auto fire with almost no recoil is still impressive.

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Now y'all tell me that a 5/8 die works on a .67 bbl haha.gif . Now I'm stuck with one threaded for 17x1unhappy.gif Gives me an excuse to buy another one and outfit it differently. Maybe I'll make the 17x1 into a classic style with wood handguards since it has the 74 break, and the next one a more modern setup.

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I was originally going to use a JP Eliminator but am not sure if I'm secure enough in my manhood to handle the ridicule I'd get from everyone who saw it.

I am still waiting on the "Big Chubby" jokes.nothing.gif

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I was originally going to use a JP Eliminator but am not sure if I'm secure enough in my manhood to handle the ridicule I'd get from everyone who saw it. Currently I'm leaning toward their "Large Profile" Tactical Compensator. It's supposed to be as effective as the Eliminator but with more conventional looks. There's a neat video on their website showing the Eliminator being fired one handed on a full auto M16. Yes, it's just a 5.56 but 30 rounds of auto fire with almost no recoil is still impressive.

 

Very impressive, just wonder how bad the side wash is? The one I have now really vents to the sides.

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Some of the ones that best take the thump off the shooter's shoulder have a tendency to put the thump back in his or her (or the person to the side's) face. I imagine the effect is magnified with shorter barrels too.

 

I was originally going to use a JP Eliminator but am not sure if I'm secure enough in my manhood to handle the ridicule I'd get from everyone who saw it.

Manly, unmanly...you're the guy with the gun.

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I was originally going to use a JP Eliminator but am not sure if I'm secure enough in my manhood to handle the ridicule I'd get from everyone who saw it.

I am still waiting on the "Big Chubby" jokes.nothing.gif

 

Well, they certainly are BIG, but I wouldn't exactly call them "Chubby".

 

Uh, you were talking about your avatar, not your brake, right?

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I was originally going to use a JP Eliminator but am not sure if I'm secure enough in my manhood to handle the ridicule I'd get from everyone who saw it. Currently I'm leaning toward their "Large Profile" Tactical Compensator. It's supposed to be as effective as the Eliminator but with more conventional looks. There's a neat video on their website showing the Eliminator being fired one handed on a full auto M16. Yes, it's just a 5.56 but 30 rounds of auto fire with almost no recoil is still impressive.

 

Very impressive, just wonder how bad the side wash is? The one I have now really vents to the sides.

 

I've never used a brake before but would bet it would be substantial on a 308. Maybe not to you, but to people standing to the sides. Of course this could be beneficial in getting you more room at the range. big_smile.gif I looked closely at the video for the Eliminator and didn't notice any caps or clothing getting blown around. Of course that might be different with the Tactical.

 

Some of the ones that best take the thump off the shooter's shoulder have a tendency to put the thump back in his or her (or the person to the side's) face. I imagine the effect is magnified with shorter barrels too.

 

I was originally going to use a JP Eliminator but am not sure if I'm secure enough in my manhood to handle the ridicule I'd get from everyone who saw it.

Manly, unmanly...you're the guy with the gun.

 

I'm good to go since I have a long barreled 308. I hope. And actually I was semi-kidding about the ridicule. I'm not sure if I would care for the Eliminator myself. I'd have to see it on my 308 first and then it would be a little late to change my mind. It certainly is a bit different.

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I was going to keep and move back my FSB. Dinzag says it will be moved about .58 back if you use the front hole in the block and the rear hole in the barrel, then drill a new rear hole. So, I assume that would leave about .58 available for threading? That would be great as the JP tech said they recommend .600. Looks like I may be ordering a brake soon.

 

BTW, my nephew owns a machine shop and I asked him if it would be possible to CNC the threads instead of trimming the barrel down and then using a die. He said he didn't see why not as long as it fit in the machine. I've sent measurements and am awaiting a reply. If it works, then my total cost might be just the cost of the brake.biggrin.png

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Rats, let me try this again...

 

Okay, so the block moves back about 0.58". It loses the front of the shroud, which will probably be offset by the addition of a jam nut or crush washer. And with the taper at the muzzle, the threads probably won't be deep enough to engage for the first...I don't know, 0.125-0.25"? So, maybe just about half an inch of thread engagement, which is 12 threads. I don't know what the best practices for muzzle devices are, but it seems pretty good to me.

Edited by DrThunder88
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I was going to keep and move back my FSB. Dinzag says it will be moved about .58 back if you use the front hole in the block and the rear hole in the barrel, then drill a new rear hole. So, I assume that would leave about .58 available for threading? That would be great as the JP tech said they recommend .600. Looks like I may be ordering a brake soon.

 

BTW, my nephew owns a machine shop and I asked him if it would be possible to CNC the threads instead of trimming the barrel down and then using a die. He said he didn't see why not as long as it fit in the machine. I've sent measurements and am awaiting a reply. If it works, then my total cost might be just the cost of the brake.biggrin.png

 

Plus a 12 pack at least, gets hot running that CNC big_smile.gif

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Rats, let me try this again...

 

Okay, so the block moves back about 0.58". It loses the front of the shroud, which will probably be offset by the addition of a jam nut or crush washer. And with the taper at the muzzle, the threads probably won't be deep enough to engage for the first...I don't know, 0.125-0.25"? So, maybe just about half an inch of thread engagement, which is 12 threads. I don't know what the best practices for muzzle devices are, but it seems pretty good to me.

 

I didn't see any mention of length of barrel left for threading, sorry. I'm not going to use a jam nut. I figured I'd drill and tap a hole in the bottom of the brake for a set screw and use loctite. We can shave the brake to get it aligned correctly.

 

I was going to keep and move back my FSB. Dinzag says it will be moved about .58 back if you use the front hole in the block and the rear hole in the barrel, then drill a new rear hole. So, I assume that would leave about .58 available for threading? That would be great as the JP tech said they recommend .600. Looks like I may be ordering a brake soon.

 

BTW, my nephew owns a machine shop and I asked him if it would be possible to CNC the threads instead of trimming the barrel down and then using a die. He said he didn't see why not as long as it fit in the machine. I've sent measurements and am awaiting a reply. If it works, then my total cost might be just the cost of the brake.biggrin.png

 

Plus a 12 pack at least, gets hot running that CNC big_smile.gif

 

I'll buy the beer of course, but his shop has AC and the CNC is enclosed so things are looking good. I'll order the brake in a day or two.

 

The only problem I'm seeing now is that I'm in Iowa and he's in Oklahoma. Fortunately, I'm going to a wedding there next month. I probably won't take the 308 to the wedding though as I don't think it's necessary at this one.

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Rats, let me try this again...

 

Okay, so the block moves back about 0.58". It loses the front of the shroud, which will probably be offset by the addition of a jam nut or crush washer. And with the taper at the muzzle, the threads probably won't be deep enough to engage for the first...I don't know, 0.125-0.25"? So, maybe just about half an inch of thread engagement, which is 12 threads. I don't know what the best practices for muzzle devices are, but it seems pretty good to me.

 

I moved mine back myself. I "reamed"the back of the sight with a dremel grinding stone and measured with my calipers until the diameter was 0.001" bigger that the bbl. I know it's not precision work but it's just the front sight. Then I was able to move it back pretty easily with a ball peen hammer and aluminum block. My bbl wasn't tapered - the front block was all the way forward - I couldn't even mount a SGM tactical muzzle break. I think mine ended up with 14 threads. I will post pics of my process soon. Converting my 308 was fun and would gladly do it again. Maybe I'll get a 22" one to work on if I can get a good deal.

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Good news.... took my FSB off yesterday and it wasn't difficult. Barrel is .670. I don't have the lip at the front of the base which is fine by me.

 

Bad news.....JP doesn't have the Large Tactical Compensator w/.750 taper in stock. They do have it in stainless but that would be the only stainless on the gun so probably won't go that route. Sent them an e-mail and hope for a response tomorrow as to when they will be available. Time can get short in a hurry so I may have to go with something else. Figures. I find what I want and then may not get to use it.

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Stainless? That's what they make stove paint for! Apart from...well, never mind.

 

I got everything done! True to Red's post, it was a struggle to turn the die beyond the taper, requiring me to brace the rifle against the bench with my body weight despite the barrel being clamped tightly between two wooden blocks, but ferus interfectus est.

 

I also got my FSB back from Dinzag after less than a week when shipping time is considered! It too is in back in place and pinned in. Everything looks great!

 

Thanks for everyone's help!

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Stainless? That's what they make stove paint for! Apart from...well, never mind.

 

I got everything done! True to Red's post, it was a struggle to turn the die beyond the taper, requiring me to brace the rifle against the bench with my body weight despite the barrel being clamped tightly between two wooden blocks, but ferus interfectus est.

 

I also got my FSB back from Dinzag after less than a week when shipping time is considered! It too is in back in place and pinned in. Everything looks great!

 

Thanks for everyone's help!

 

Painting it would be more time/hassle but is an option. I wouldn't want to put it on and never get around to painting it though. I could go with a PWS FSC30 as an alternative. I figure I'll just turn the barrel to .670 where I need to move the sight block back to. The block doesn't seem to be overly thick any way. Yours have a lip up front? Mine didn't.

 

Glad yours worked out without having to shave the barrel down. That saved you lots of money.

 

It's gonna be a while before I get mine done but I will try to post pics at that time. I'm photographically challenged but the wife and daughter in law should be able to do it.

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