3-20x50 SB PMII (std) MTC Lockable Problem

[CBB15]

I have a very lightly used PMII standard length 3-20 with the lockable MTC turrets. It was briefly mounted on a 308 before sitting a while and mounting on a new rifle. Ran perfectly before removing and remounting.

Issue: Neither the elevation, nor windage turrets are zeroing per the procedure. Another words, with the 2 retainer screws loosened, the turret still moves the reticle. I have tried multiple times and I am not able to set the turret at zero without moving the reticle. Otherwise it is tracking perfectly...

Procedure:
1. sight in (8.6 mils @ 100yd zero)
2. lock both turrets
3. loosen elevation turret retainer screws;
4. unlock turrets
5. dial elevation back to zero
6. follow procedure with windage (minimal)
7. fire for confirmation.
8. impact off 8.6 mils.

What am I doing wrong here? It has been a while. This has go to be user error for both turrets to act the same...

 

[Dogtown]

I had this happen a while back. Confirmed by mounting it, loosening the screws, the dialing elevation only to watch the image move. An email to S&B got the fix rolling. They sent it back to me the day it arrived - very quick turn around.

 

[CBB15]

^ Plan A

 

[CS95]

this happens on the S&B DT turrets when you over torque the turret set screws. The over torqued screws create a raised burr. That burr contacts the turret cap and causes the turret screw to turn with the cap.
If you are mechanically inclined is a pretty easy fix. If not, you will need to send it in for service.

 

[Kiba]

this happens on the S&B DT turrets when you over torque the turret set screws. The over torqued screws create a raised burr. That burr contacts the turret cap and causes the turret screw to turn with the cap.
If you are mechanically inclined is a pretty easy fix. If not, you will need to send it in for service.

While that can happen, the more common reason for this happening on the MTC/LT turrets is the 3rd (plugged head) knob retention set screw is just a smidge too tight so it drags the spindle along for the ride moving the reticle when trying to zero the turret even though the other 2 (unplugged / zero adjustment) setscrews are loose.

The elevation turrets on 2 of my 3 S&B 3-20s had this issue right out of the box. The first time I sent it back to fix, the next one I fixed myself.

Easy fix: Send it to S&B.

DIY fix:

1. Loosen 2x zeroing (unplugged head) setscrews
2. Remove plastic plug from hex of 3rd ( turret retention) setscrew using dental pick
3. Remove 3rd setscrew (you may have to very slightly lift the knob while simultaneously pressing the lock ring down a bit lower to clear, don’t lift it too much or the detent pins in the turret can pop out of their grooves and rotate and you can lose either the 0.1 or 1.0 mil clicks, and then you have to completely disassemble the turret to reset the detent pins.)
4. Apply a tiny bit of low or medium strength Loctite to the removed 3rd setscrew
5. Reinstall 3rd setscrew into knob, and while pushing the turret down tighten the setscrew until you feel it just barely contact the spindle
6. Loosen the setscrew approximately ¼ turn from the “light contact” position. It needs to be loose enough not to drag the spindle when you try to zero the turret, but tight enough the tip of the setscrew is in still engaged into the groove of the turret spindle so it prevents you from pulling the turret off the scope when you have the 2x “zeroing” setscrews loose to zero the turret. Right now it’s a good idea to look through the scope at something while rotating the turret to make sure the reticle isn’t moving… it will click, but the reticle should not move. If it is moving, the 3rd setscrew that you just reinstalled is still a bit too tight. Loosen it just a tiny bit more and try again. If the reticle isn’t moving as you spin the turret, everything is OK—let the Loctite set up.
7. Reinstall plug into 3rd setscrew.

If that doesn't work, it may be burrs on the spindles from overtightening the set screws. In that case you need to pull the turrets apart and carefully smooth the burrs. The MTC/LT turrets can be a bit tricky to reinstall and it's easy to lose or mess up the 2x detents and springs, but they aren't bad if you're mechanically inclined. Safest bet is to send it to S&B though.

 

[47chevycoe]

What Kiba said. I had it happen to a brand new 3-20. Jerry got me going over the phone.