rlwilson
Well-Known Member
http://bulletin.accurateshooter.com/2015/04/muzzle-threading-dont-remove-too-much-steel/
Take this for what it is worth, it is interesting.
Take this for what it is worth, it is interesting.
Muzzle threading
- Thread starter Demon061
- Start date
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Yes, very interesting. I've always read that the muzzle bore diameter should never be larger than the rest of the bore for best accuracy, and now it seems that cutting threads at the muzzle increases bore diameter at the muzzle. What to do??? I'm getting ready to put a couple brakes on barrels now. I may epoxy glue and roll pin them on, after lathing the ID of the brakes and the OD of the muzzles to uniform diameters for a close and snug slip fit. Sounds crazy but it seems like this will work. Maybe not as pretty as a nicely fitted threaded brake, but I'm into function more than looks.
Hired Gun
Well-Known Member
My specialty is super precise barrel work. We discovered this years ago. It's worse on button rifled barrels than cut rifled. When the brake is torqued up the bore size is restored. If you go too tight it will make the bore constrict giving you a choke if you want it. About 15-20 foot pounds is about right on the thinner installs. Banded front sights fall in the same category. The barrel must be cut to fit and it relieves it slightly. The heat from the silver solder job shrinks them back and sometimes it constricts it.
Fluting does the same thing causing the bore to expand. I feel it every time I slug a new barrel. With my eyes closed on the lighter contours I can feel exactly where fluting starts and stops. It's just something to be aware of and to look for. Just check it with a snug bushing when you are done. After you have done a few you get a feel for how much crush is needed to get it right. Same as cutting barrel tennons for headspace or timing flutes.
A roll pin this close to the bore may distort the interior just as much but only unevenly. I wouldn't do that one unless it was really small loosely fitted pin like the barrel pin in a S&W revolver. On a light barrel the threaded clamp style is not too bad as long as you don't crank the screws down but the smooth clamp on brakes really squeeze the bore when they are tight enough to stay on. We pull these regularly and put them in our scrap bin with the factory barrels and machining chips. I get about $50 for a garbage can full of them.
J E Custom
Well-Known Member
It is interesting, Thanks.
After seeing the video I decided to look/check some of the barrels that I have for this "condition"
because the largest threads I have used are 1/2x32 to 7/8x14 for muzzle brakes. I used reamer bushings that were tight at the muzzle and they all went well past the thread shoulder.
I did not find this phenomena in any of them, I did find barrels that were .000+at the muzzle because when the barrel maker contours a barrel he will place the tightest bore at the muzzle
(some even make a cut to force you to remove some of the barrel end because of lapping
wear).
The only place I have seen this barrel bore loosens at the muzzle is on rifles that were cleaned from the muzzle. (The cleaning rods wear the muzzle).
I always use the largest threads possible and use double stress relieved barrels. I don't know it this is the reason that I did not find any problems with increasing bore diameters, But if the threads are not properly cut, and the barrel wall is to thin, and the brake is over tightened it is possible to create a condition that could hurt accuracy.
So In my opinion, Thread size has nothing to do with this condition if done properly. It would be nice if every rifle had a barrel large enough to place 7/8 threads or larger on, but that is just not going to happen because most barrels are to small for even 11/16 threads and 5/8 threads can't be used sometimes.
I for one will keep checking for my self to see if this occurs and if it does why.
Thanks again. It does bring up questions and concerns.
J E CUSTOM
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It's a lot to ponder haha.
Yeah, I know what you mean.
But I finally obtained enough input to make my decisions.MSU Marksman
Well-Known Member
I also read this article and became concerned about what threading a muzzle might do to a barrel. I suspect that how the muzzle is threaded might also be a factor into the bore expansion. It would seem if a cutting tool took multiple passes, it could overheat the metal. Maybe fewer passes with more cooling/cutting oil makes a difference?
J E Custom
Well-Known Member
There are many things that could upset the muzzle of a barrel while/when threading or fitting a muzzle brake to it.
First the barrel must be is a state or stress relieve that makes the barrel material very stable.
Different ways of cutting the threads could effect the diameter of the threaded tenon. when rolled
threading is used(Lots of bolts are roll threaded)this could cause the diameter to change,
Using a die will also change the diameter if the wall thickness is minimum because of the inward force on the tenon from all of the cutters cutting at the same time. a proper Lathe cut thread should be stress free and should not cause any dimensional changes. Heat is always an issue and multiple
passes are the best way to avoid heating the tenon up.
There is another way to alter the bore diameter that is more common. When a muzzle brake or a barrel nut is installed on a marginally thin barrel wall as the brake is tightened it will reduce the bore diameter because if the 60o angle of the threads. to avoid this some smiths use Loctite and hand tight fit ups.
So in my opinion, if the barrel is properly stress relieved and threads are cut properly and the brake is installed properly there should not be any diameter changes to the bore.
J E CUSTOM
