Question On Muzzle Threading

V

V35B

Registered
Registered
Joined
Mar 27, 2020
Messages
27
This will seem elementary to most, and I think i know, but need assurance.
So, I am threading the muzzle for a suppressor on one of my older AR’s that didn’t come threaded. Doing the work is no problem, but indicating it is. I have a spider on the outboard side, and the four jaw with some aluminum shims on the other. I used the Gordy or Grizzly rod with a bushing that has a really good no play slip fit. I indicated the last 2” of the barrel within .0003” with the rod, by moving it in and out with the tail stock. The question I have is that when pulling the rod in and out, the indicated reading is .003” different between the two inches, I am thinking this is ok, since both points were indicated concentric to the center of the spindle bore, and there is just some variation in the rod or something. Is this normal or ok for this?
 
I have never threaded a barrel in a lathe, but it is my understanding that the work should be done between centers. The bore is not always in the exact center of the barrel.
 
I use the tightest slip fit deltronic pin I can out of the muzzle and use the 4 jaw to indicate it in. I leave an inch or so our of the barrel and dial it in to within .0001. Check that it is straight by running the DTI right at the muzzle and at the end of the pin and make sure they are not different (or at least very close). The spider is just to support the breech end. If you are square where it comes out of the muzzle you are ok. Look through it with the suppressor on when done and you can tell pretty quick it there are any issues.
 
Turn it between barrel plugs ! :encourage:
 
You can indicate the barrel concentric on both ends and it can still be off axis to the bed ways. With the rod sticking out at least a few inches you indicate the rod close to the muzzle with the 4 jaw. Then you indicate the rod a few inches away from the muzzle via the out board spider. This will likely throw off the concentricity of the rod at the muzzle so you fix that again with the 4 jaw. You go back and for using the spider and the 4 jaw until the rod is concentric both at the muzzle and a few inches out. Then you will be dead nuts parallel with the lathe axis and your threads will be square.
 
Last edited:
Large to small , we always did them this way . :encourage:
 
There's lots of ways.

Inboard / outboard spiders, 4 jaw with brass pads, a ring. Indicate a range rod/gauge pin in each end of the barrel.

Or, inboard /outboard spiders, range rod protruding from muzzle end, indicate @ 2 points, or indicate by sweeping indicator down the length of the rod, rotate the spindle 90° and sweep again.

Or, some combination of the above methods.

Between centers is an oldy, and one of my favorites just because it's so fast and easy.

For suppressors it's important to have it dialed in accurately. Especially minimizing the axial runout. The zero / POI shift caused by the baffle bore axis and barrel bore axis not being coaxial and collinear can be extreme.

Even if there's no baffle strike, I've seen suppressors with the muzzle end hole .01" off the barrels bore axis cause a couple mils of POI shift on target.
 
Last edited:
V35B said:
This will seem elementary to most, and I think i know, but need assurance.
So, I am threading the muzzle for a suppressor on one of my older AR’s that didn’t come threaded. Doing the work is no problem, but indicating it is. I have a spider on the outboard side, and the four jaw with some aluminum shims on the other. I used the Gordy or Grizzly rod with a bushing that has a really good no play slip fit. I indicated the last 2” of the barrel within .0003” with the rod, by moving it in and out with the tail stock. The question I have is that when pulling the rod in and out, the indicated reading is .003” different between the two inches, I am thinking this is ok, since both points were indicated concentric to the center of the spindle bore, and there is just some variation in the rod or something. Is this normal or ok for this?
Click to expand...
I use the tightest slip fit deltronic pin I can out of the muzzle and use the 4 jaw to indicate it in. I leave an inch or so our of the barrel and dial it in to within .0001. Check that it is straight by running the DTI right at the muzzle and at the end of the pin and make sure they are not different (or at least very close). The spider is just to support the breech end.
 
You must log in or register to reply here.
Back
Top