How I thread a rifle muzzle

[Ian]

This is a .30-caliber barrel for which the standard thread is 5/8 X 24, but with a medium sporter profile the muzzle diameter is .633". That means there isn't enough barrel diameter to form an adequate shoulder for the muzzle device. That leaves two options: Threading to a smaller standard size, or indexing off of the muzzle face inside the brake. I chose the former and one option is 14 X 1.0 mm, a standard for the AK-47.

Step one is indicate the barreled action true to the bore center through the headstock. I use a gague pin turned to a slip fit in the muzzle (an old bolt in this case).



The other end is more tricky, I usually indicate off of the outside of the barrel to get close and then use a wire clamped to a fixture to reach up inside the action and indicate wobble inside the chamber.



This is the outboard spider I made just for this sort of thing. Barrel is protected by an aluminum sleeve here and by a large copper wire bent into a ring and held in the notches of the chuck jaws. The wire ring in the jaws eases stress on the barrel as it only bears on one point rather than the whole length of the chuck jaws.

 

[Ian]

Step two is set up a cutting tool and peel back the muzzle to the thread major OD and shoulder length that the brake requires.



Then cut the relief down to a little smaller than thread minor diameter (I use a cut-off blade with the left shoulder radiused to prevent a stress raiser).

 

[Ian]

Next I chamfer the end, set up my gears, and scratch in the metric, left-handed threads.



Then cut the threads down as required either to a standard using pitch wires (I do this on most of my rifles so that any brake will fit rather than individually fitting parts), or in this case just until the brake will thread on. I do the usual spring passes and work the burr edge back and forth with a file and more spring passes and finally touch up the threads with a Scotch pad. After a good fit is achieved, I face the shoulder to index the brake so that no shims are required (again, only in a custom-fit application, otherwise I adhere to the established standards for shoulder length).

 

[Ian]

Last step is installing the brake. These are my pitch wires that I use together with a c-clamp micrometer and the included chart to meet standard sizes and classes of fit as required.






After checking for alignment with the suppressor installed, I pull the brake one last time and put a drop of blue threadlocker on the threads, tjen re-torque it and check alignment again. Done.

 

[Ben]

Nice work !!!!!!!!!!!

 

[Gary]

Impressive, I must say. BTW, the outboard Spider; is it threaded to the Spindle or press fit within the Spindle?

 

[Ole_270]

Mic'ing over 3 wires can be fun when you're as fumble fingered as me!

 

[Ole_270]

I had a little more dexterity the first time I did it in trade school back in 1973, just couldn't slow down long enough to do it right. Nowadays I'm plenty slow, just stiff as a board and can't see either.

 

[Ian]

I tape two of them together with the right spacing with masking tape, then hold them in place with the mic while holding the third wire under the thimble anvil with my other hand and then work the thimble and wiggle the mic over the center with my third hand.

Gary asked me if I would document and post this process, it's all very basic lathe work but does require a high degree of precision and the sequence of steps worked out.

Metric threading is a whole other thing if you haven't done it....my lathe (like many, especially 'Murican iron) requires leaving the half-nuts engaged for the entire threading operation, so there's lots of reversing the spindle with everything still engaged and telling yourself DO NOT POP THE HALF-NUT LEVER!!! at the end of every single pass of the threads. At least these were left-handed and I could thread away from the spindle.

 

[Spindrift]

Very nice work!

 

[Wasalmonslayer]

Nice work Ian!

Have good tooling sure make projects more enjoyable.
I am in the hunt for a four jaw Chuck right not.
The three jaw I have is decent but I have no ability to set up and tru my pieces to zero run out.
Using shims is a pain and time consuming to set up.

 

[Ian]

Gary, the outboard spider I made for this particular lathe replaced the outer spindle nut. The speed sensor reluctor is also a tang washer that sandwiches between the inner spindle nut and outer (now the spider) and locks the nuts to the shaft. That was my first threading project, female metric threads against an internal shoulder on a steel part that couldn't be removed for test fitting without losing the threading index or alignment.

Max, I got so used to using a 4-jaw independent that I don't switch back to the 3-jaw much anymore. Most of the work I've been doing on guns and reloading tools requires internal work on a part that has a finished OD so it has to be indicated precisely anyway. If you have a big enough lathe and deep enough pockets, a 6-jaw chuck like Will Quiles has would be the ultimate solution for speed and precision.

 

[smokeywolf]

At least these were left-handed and I could thread away from the spindle.

You can also "thread away from the spindle" (or a shoulder) when cutting a right hand thread. Just flip your single point cutter upside down in the tool holder and reverse your spindle. Make sure your tool holder is locked in tight on your tool post.

 

[wquiles]

Nice work Ian !!!

 

[Ian]

You can also "thread away from the spindle" (or a shoulder) when cutting a right hand thread. Just flip your single point cutter upside down in the tool holder and reverse your spindle. Make sure your tool holder is locked in tight on your tool post.

The lantern post that came with this little 7x14 lathe didn't have enough adjustment to do that without a longer stud and stacking spacers under it. I just recently acquired an OXA-sized QCTP which should have enough adjustment to thread upside-down and away, so I'm definitely going to try that with your caveat about the tool holder and a great deal of caution regarding the strength of my compound gibs.