recessed crown under barrel threads?

Discussion in 'Gunsmithing' started by foreign, Apr 14, 2014.

  1. foreign

    foreign Well-Known Member

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    so you here people saying that threading the end of the muzzel can cause the id of the barrel to open up a little because you are removing material. Well i was just thinking. Why not cut the threads and then crown the barrel with a recessed crown so that the crown is back behind the start of the threads in the barrel. Obviously it depends on how long you threads are as to how far you recess the crown.

    Anyone tried it?
     

  2. Canadian Bushman

    Canadian Bushman Well-Known Member

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    I dont think it will be any better than any other crown. Ive threaded a few barrels and never seen accuracy or velocity loss after threading, as long as the correct thread is used.

    My hunting rifle is a 30 cal chromoly barrel threaded 5/8-24 with an 11 deg crown and it shot exactly the same after threading the muzzle .75" back.
     

  3. Hired Gun

    Hired Gun Well-Known Member

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    On a regular Remington or Winchester sporter barrel the largest thread you can get on there and still have any shoulder is 1/2-28. On a .308 cal this leaves the barrel pretty thin. I haven't noticed the bushing or lead slug fitting loose enough to lose accuracy. I have frequently found that even with much thicker barrels, if the brake is put on too tight it will measurably constrict the barrel. Again accuracy rarely suffers from this effect.

    Cutting a crown .600" deep before where a brakes baffles begin would make for a very weird installation. I like the end of the muzzle to end exactly where the port starts and taper back at 11 degrees to the crown.
     
  4. foreign

    foreign Well-Known Member

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    HG. by put o too tight do you meant he thread fit is tight or do you mean the brake is torqued on tight? how tight is too tight have you found? does this make it hard to then make for a "seamless" looking joint if the brake isnt tight?

    It would be interesting if someone tried it. take a barrel with a break already on, measure the tenon length of the thread and then counter bore a crown slightly deeper than this.
     
  5. Hired Gun

    Hired Gun Well-Known Member

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    I meant torqued too tight. It can happed from around 15 foot pounds and up. On big threads it might take a hundred to constrict the bore. There is no set rule. It happens when it happens.

    For a truly seamless fit it usually needs the joint sanded with the barrel. How tight it is has little to do with that. Don't be impressed by seamless fits when they are sanded. That is simple. Be impressed when a stainless brake is seamless up to a blued or coated barrel. That takes a sharp eye and a spot on dialing in on the outside of the barrel.
     
  6. J E Custom

    J E Custom Well-Known Member

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    +1
    I have never seen any loss or gain in barrel/bore diameter doing it the same way as Hired Gun, so ether I have been lucky or just picked the right way to install a brake.

    If you have a good class 1 thread fit I can see no down side.

    Like many others I subscribe to the "KISS" method (Keep it simple stupid) and don,t over complicate
    things and concern my self with the quality of work and components.

    J E CUSTOM
     
  7. Hired Gun

    Hired Gun Well-Known Member

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    JE,
    Have you ever really looked for the change in bore diameter? I found it by accident. I had a custom in from another smith with a brake on it for a barrel inspection. I cleaned it and visually inspected it and found nothing remarkable about the bore. I moved on to slugging it to check uniformity of the bore and found that it was really tight right in the brake threads. I loosened the brake and that cleared the constriction. That was how I discovered the bore constriction thing and then I went looking for it on every thread job. The best thread fit there is makes no difference. If the brake is torqued too tight it will constrict the bore. I can find it with bushings. Before you thread find the largest that will still go and when you are done with the brake job see if it will still fit. I found the small thin walled thread jobs were really susceptible to it. I originally just started not using so much torque but then had one come loose on a guy after a couple hundred rounds. So now rather than relying fully on torque I use blue Loctite on the thinner barrels.
     
  8. J E Custom

    J E Custom Well-Known Member

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    I am anal about everything and check the bore before I start and then after I thread to see if the stress relieve was good (If not stress relieved properly the bore can increase because of the loss of material
    removal).

    After I install the brake I gauge the brake and the bore to make sure everything is in alignment
    but in the past I have not mike'd the bore after the brake installation but have since started to
    see if the torque had any effect on the bore. (So far I have note seen any measurable change)

    I also use the largest thread possible to leave the tenon as large as possible and maintain a minimum of .175 wall thickness based on the bore dia.

    Some barrels are to small for threading and fluting because the wall thickness gets to thin based on the bore so I don't/won't do them. That may be the reason I have not had that problem (Luck and caution).

    I will however continue to check for this now that it has been brought up.

    Thanks for the insight, We are never to old to learn.

    J E CUSTOM
     
  9. Trickymissfit

    Trickymissfit Well-Known Member

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    According to Bill Calfee the bore does open up slightly. I did a tuner on a Cooper Rimfire several years back, and I could feel it with a tight patch. And that was from just cleaning up about 1.25" of the barrel and threading it with a very fine thread (think it was 32tpi or 40tpi). Had I to do over, I'd have done a tapered thread with a steel body on the tuner.
    gary
     
  10. Hired Gun

    Hired Gun Well-Known Member

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    Sporter barreled 300 RUMs are my number one muzzle brake demand. Are you refusing these guys?
     
  11. J E Custom

    J E Custom Well-Known Member

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    Not at all, Normally the Rums are on a magnum barrel contour and have enough barrel to accommodate
    a threaded tenon as long as the proper size is used.

    Some barrels are however, to small at the muzzle to thread or flute and I recommend those barrels
    be replaced with a heaver contour.

    Barrel makers won't normally flute if the wall thickness will end up less than .137 Thick after
    fluting and/or threading.

    Even though I personally don't like clamp on brakes if installed correctly they will work under these conditions.

    J E CUSTOM
     
  12. Trickymissfit

    Trickymissfit Well-Known Member

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    you can also simply cut holes in the end of the barrel with an EDM. It adds or relives very little if any stress in the barrel, and leaves very little if any burr in the bore. The problem is finding an EDM big enough to do it (they're out there), and the cost maybe be a good bit more due it being a little on the slow side (cuts about .06" a minute). The good part is that you can cut the non symmetrical holes that some folks this are best.
    gary
     
  13. J E Custom

    J E Custom Well-Known Member

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    Gary. No argument, just a comment.

    I have some ported barrels that have been EDM Machined and The testing I have done doesn't make it very cost effective to have this done.

    Porting the barrel does work, but I have found the recoil reduction to be 10% to 20% at best and the cost is close to the cost of having a brake installed + you do lose some velocity.

    It looks cool but IMO it is not worth the effort any more on rifles. It is still a viable process for pistols that need some muzzle control and a brake would ruin the value/looks of a fine pistol.

    As I have said before, I don't like clamp on brakes because of looks and if done properly, the
    barrel taper should be removed so the brake can be installed (This needs to be performed in a Lathe
    to be true to the bore, and the bore diameter should be bored after the brake is installed to assure
    alignment.

    So IMO if recoil is an issue, A good muzzle brake is still the best way to get the most bang for your buck.

    Just my opinion.

    J E CUSTOM
     
  14. Trickymissfit

    Trickymissfit Well-Known Member

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    I thought I pretty much
    spelled out the bad part of EDM porting. Most EDM machines are not big enough to begin to handle the barrel length alone. Still the EDM opens up a huge venue for you.

    The one thing about a threaded mount is the thread fit and alignment of the bore to the barrel bore.
    gary