Scope rail screw broken! Cause and fix.

Well, finally found the perfect load and mounted new Vortex Viper G2 on the 300WM. Perfect zero at 100 yards with .25 groups! Then....🤬!

When I moved to the 300 yard range, shot 1 shot bullseye. Happy hunter. While looking through scope, I touched the objective bell and noticed my reticle jump across the target, then back again. WTH??? Factory mounted scope rail was loose. (Yes, I checked that it was tight before mounting scope, ‘assuming’ that the factory mounted it correctly.). When I removed the scope, I found that the screw over the barrel nut was broken. I understand that this is not an isolated case, as my brother in laws Stealth did the same thing! Here’s what we found, and presume the reason why.

The magnum “long distance guns” come with a 20moa scope mount. After inspection of the mounting holes, they are not threaded all the way down to the chamber to prevent the 6x48x1/4” screws from hitting the bolt. This wouldn’t be, or isn’t an issue if you are not using a 20 or 30 MOA canted scope rail, but with the reduced thickness at the front of the scope rail, the factory uses the same screw length on the front as on the rear or thick end of the scope rail. Subsequently, when the factory mounts the 20 MOA rail, the screws do not fully tighten on the rail, and if torqued to the bottom of the threads, can compromise or break the screw. Even a bigger problem with a 30 MOA rail! Have seen this same issue on two guns I have access to and heard of this as a problem on an older forum. This should be addressed and hopefully fixed by the factory.

i was able to remove the broken screw using an Irwin EX-1 screw remover (With drill bit) for about $4. You’ll need a drill press and GO SLOW when drilling out the broken screw. The bit is small enough not to damage threads if you center your bit correctly. The remainder of the screw came out easily with the left handed screw remover.

The correct fix for this is to re-tap the holes to continue the threads all the way through. You will need to shorten the screws with a grinder or such and make sure they do not protrude all the way through. If you only shorten the screw, you will only have a few threads to hold the rail. May be ok, might not. Depends if you may want to get another case of turrets at the range again.

Hope this helps, but really hope Savage fixes this problem!

You only need to repair the threads if you damaged the old ones. If you drilled off center etc.... Since you have it mounted in a drill press. go ahead and open both holes up and tap the new thread. A mill would be better because you could power tap without having to deal with busted taps. Next you will have to open up the holes in the base. The new drill will follow the old hole within a .001" or so. a center drill will work for the tapered head screws but the angle may be slightly off. otherwise you will need to find the correct drill and countersink.


The front screw will always be short due to the wall thickness of the action and the diameter of the barrel threads. You could divot the threads but I would not go below the root of the thread.

You must have the exception to the rule, as I have yet to see any scope base threads that didn't go all the way through the receiver.

Huh. Now that you mention it, me neither.

Quote:

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Originally Posted by sharpshooter

You must have the exception to the rule, as I have yet to see any scope base threads that didn't go all the way through the receiver.

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I think the barrel threads where at the bottom of his hole.

A few years back on one of the shooting forums a guy had his gun blown up after a home fix to a broken scope base screw. Seems he drilled it out (completely through the barrel into the chamber).......blew the screw/base scope and more damage...scary...and pretty "hack job"....
Now there was probably a real "Turrette's" outburst after that. (Still chuckling about the OPs comment).

Any way removing the barrel and resizing to .146-48 (Brownells) or even 8-40 and grinding the new screws to exact length should solve the problem. Machining new c-bores for 8-40s may be required. Offsetting the rail fore or aft and machining 4 new c-bores for the longest possible screws would be a better option.
Bedding the rail may also help.
On a side note also recheck the torque on the action screws. Extra flex in the action may have contributed to extra strain on the screws & rail if the stock was loose and allowing more flex. Similar stresses can be placed on the action by using a heavy weighted led sled.
Lastly because it is a 300WM can we assume it is a small shank? The WSM would certainly be a large shank. The large shank actions have even less threads in the receiver and full thread engagement is mandatory.

Just food for thought.

Bogboy, resizing to the .146 is not an option if the factory threads are damaged. If you put the calipers on a #6 tap you will see what I'm talking about. The #8-40 is the best option you gave.

Bogboy, resizing to the .146 is not an option if the factory threads are damaged. If you put the calipers on a #6 tap you will see what I'm talking about. The #8-40 is the best option you gave.

Robin, thanks for the correction
I agree if the threads were damaged. My take was the OP didn't damage them but only thought they should be deeper (even though most of us believe that are already tapped through). The .146-48 option would tighten up the existing threads only. The 8-40, of coarse, would definitely have more "holding" ability as we all agree.
Hope my previous post didn't mislead anybody.

One of the best methods I've found for removing broken screws is to use a left twist drill. As the drill bites into the screw it'll most often back the screw right out before you even get halfway down into the screw. This eliminates using an extractor which frequently expands the screw, making removal even harder. Left twist drill are available in most sizes.