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Thread: Suppressor threading

  1. #1
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    Default Suppressor threading

    Mossberg 100 ATR 243 Needs to be threaded for a suppressor
    The suppressor is for 223 and needs a bit more clearance the thread is 14 x 1 M.
    On mounting the barrel in the lathe I have a .001 run out at the 4 jaw Indicated off the barrel external just out side the action as haven't taken the action off the barrel I think that is fine but I have a .030 run out half way down and .015 run out at the tail stock end the live center mounted in the bore as it will be re crowned so the bore is not center to the barrel apparently not uncommon so the barrel is not straight the question is. Do I place the barrel over two wooden V blocks and take .015 out of the bend or .030 out or just leave it as it is as it doesn't appear to be a problem ? Any suggestions please

  2. #2
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    Heh.

    You're just discovered that the outside of commercially produced rifle barrels are now not concentric with the bore - sometimes wildly not so. I've had barrels in my lathe that have been off half as much as you have there, sometimes more, sometimes less. That barrel is not bent, it just hasn't been turned true to the bore. It was probably put onto a barrel spinner and then had the finish of the barrel ground on a belt grinder, which leaves high/low spots. If you're not checking the barrel optically for straightness, don't assume from your readings that the barrel is bent.

    This is why, when I'm doing operations similar to what you're doing (and I want the results to be correct), I do the following:

    1. I mount the barrel through the headstock. I have a spider on the outboard end of the spindle, and the brass screws in the spider are timed up with the four jaws of my four-jaw chuck.

    2. I use #6 AWS bare copper wide on the jaws of my 4-jaw chuck to allow the barrel to pivot in the jaws.

    3. I use range rods and indicator rods in a barrel to get the barrel dialed in. I'm indicating off the rod, which is fit to the bore, so I'm dialing in effectively off the bore. You could use a test indicator with the tip inside the bore (the muzzle for what you're doing), but the next operation really needs the rods.

    4. With the longer rod in the barrel, I then dial in the far end of the rod to be as true as the rod where it just goes into the muzzle. This way, I know I have the last two inches of the bore to be straight and true. This takes some time, running the indicator up/down the rod, looking for the rod to be turning true. You'll have to adjust both the chuck and the spider to get it trued up. Typically, I get the rod just outside the muzzle dialed in first, then I move the indicator out to the end of the rod, then I get that trued up by adjusting the spider, then I'll have to come back to the muzzle and re-adjust the chuck, then the end of the rod and the spider again. It typically takes me 10+ minutes to get everything set up just the way I want it.

    Then I'll thread (or turn on a tenon and then chamber).

    Most mass produced barrels these days are no longer true to the bore. You cannot dial in off the outside profile of the barrel and expect proper results.

    OK, there's one more technique which you could use, and that's to make a brass dead center in your lathe so you can get the chamber end of the barrel true to the axis of rotation, than use the live center in the tailstock to hold the muzzle end. For this to work, you need to pull the action off the barrel.

    Edit: On lathes that are long through the headstock, or barrels that are too short for your headstock, what I do is make a barrel extension. I drill/thread the end of a 1.125" piece of round stock (eg, stressproof) to be like the rifle's receiver. For AR-15 barrels, I just bore out the barrel extension to be the OD of the barrel extension on the barrel, and I use a couple of small set screws. With this longer piece of steel added to the barrel, you can thread/chamber through the headstock of even very large lathes that are feet long.
    Last edited by wyop; 09-02-2019 at 09:37 PM.

  3. #3
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    Thanks for that WYOP I reset up this arvo and got it done thanks for your help it doesn't come as a surprise that mass produced barrels are not concentric with the bore my head stock is 11/22"ID X 22" long with out a chuck fitted so I would of had to of made an inboard spider on the LO spindle So just spun between centers

  4. #4
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    Quote Originally Posted by Kiwi View Post
    Thanks for that WYOP I reset up this arvo and got it done thanks for your help it doesn't come as a surprise that mass produced barrels are not concentric with the bore my head stock is 11/22"ID X 22" long with out a chuck fitted so I would of had to of made an inboard spider on the LO spindle So just spun between centers
    Plenty of fine rifles have been made by gunsmiths working between centers.

    When I'm working on a barrel between centers and I need to chamber, crown or thread, I will:

    1. Put the barrel between centers
    2. Turn a small stripe near the end I need to work to be concentric, then
    3. Mount up the steady rest.

    The key to working through a steady rest is getting the OD to be concentric with the ID, and to do that, you need to turn a stripe on the barrel. You can work out the surface of the barrel to match later on...

  5. #5
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    Quote Originally Posted by wyop View Post

    The key to working through a steady rest is getting the OD to be concentric with the ID, and to do that, you need to turn a stripe on the barrel. You can work out the surface of the barrel to match later on...
    Another option is to use a cat's head (maybe the wrong term, but a tube with a spider on each end) mounted to the barrel, and turn a stripe on that for the steady rest. That avoids damaging the barrel's finish, which is important sometimes.

    Your post about how to set up barrels for threading is right on. For this thread, I think the #1 point to make is to never indicate off the OD for barrel threading (at either end).

  6. #6
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    Quote Originally Posted by Yondering View Post
    Another option is to use a cat's head (maybe the wrong term, but a tube with a spider on each end) mounted to the barrel, and turn a stripe on that for the steady rest. That avoids damaging the barrel's finish, which is important sometimes.

    Your post about how to set up barrels for threading is right on. For this thread, I think the #1 point to make is to never indicate off the OD for barrel threading (at either end).
    Absolutely true, and I've helped coach people in making one of those. A thick-walled aluminum tube is what I've used for that sort of job.

    Likewise, you can use a similar setup for truing a rifle action that has something other than a round exterior profile (eg, Mauser or M70).

  7. #7
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    Cats head and spider the same ?

  8. #8
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  9. #9
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    Quote Originally Posted by H380 View Post
    Yep. That's basically what I'm talking about.

    Next widget that helps is a LaBounty bolt fixture. You can make it yourself, but if you're going to true up the face of a bolt, or bush the firing pin, they're a neat little gadget to have.

    Another tool I use quite a bit is a mandrel that I put through a Mauser, Springfield or M70 action so I can true up the face of the action. What I do that's different than some other folks is I have a set of gage pins from about 0.695 to 0.705" in increments of 0.0005. This way, I can make a mandrel that has little to no slop. I drill and tap a hole across the mandrel for a 1/4-20 bolt, so I can use a flat washer and a 1/4-20 capscrew to keep the action from turning. I mount the action mandrel between centers, drive it with a dog, and then I can take a light cut on the face of the action to get the face of the action as square as possible with the bolt axis.

    The irony about gunsmithing at times is that I do more machining for jogs, fixtures and setups than I do machining on actual guns or gun parts.

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