6-48 screws too small for 300 Win - M700? Adivice?

[Whelen B]

Using Talley lightweights and was wondering if it was wise to upgrade to bigger 8-40s. Talley has rings/screws in 8-40 available as an option. The rifle comes D&T for 6-48s - has a 26" tube and is 9.5 lbs alone. It's a Long Range so probably will have a larger and heavier scope like a nightforce on it - though not decided upon yet.

Any one ever shear or break off the smaller 6-48s?

Thanks

WB

 

[guntech]

I have never encountered a need to re drill and re tap 6x48 threads to 8x40 in almost 50 years of gunsmithing. I have seen extremely heavy accessories on a mount securely held in place by 4 6x48 screws.

Have your Talleys lapped, they all require it...

 

[hoytcanon]

The above experienced opinion not withstanding... I personally have a lot more confidence in 8-40's... if it were for a remote or particularly rough hunt, I would probably do it up front... for general use, I would wait until it is required... perhaps it never will be.

 

[Dogleg]

I've never sheared a 6-48 screw on a base yet, and that covers heavy use on rifles that make a 300 feel like a .22. Have had a couple of the small screws strip out for no good reason and those rifles got redrilled to 8-40. One was braked 338 Edge with that curious push pull recoil and hevy Mark 4 scope.

No need to make trouble where there is none, but you can do it if it makes you feel better.

 

[Leeper]

The shear strength of the smaller screw does not even enter into the equation unless you, for some reason, lubricate your scope bases. It is the static friction between the base and the receiver which keeps the mount in place. The screw provides the compression force which causes the bases to stick. At the same torque value, the amount of compression provided by a 6-48 and an 8-40 is just the same. The only difference is that the larger screw should be able to handle more torque.
I have to say though, given the popularity of the big, heavy scopes in recent years, it might be time to re-vistit scope mounting. I think the one thing that really glares out at me in the original post is the intention to mount a heavy scope on the rifle. That being the case, why the lightweight mounts? Plainly, there is no need for the weight savings and it makes more sense, to me, to go for the strongest mount system. A one piece steel base with a precisely fitted recoil step bearing against the receiver ring and a dowel into the bridge should do it. Add the HD rings of your choice and there you have it.

 

[Whelen B]

Have your Talleys lapped, they all require it...

Will do. Have a friend who has the equipment for that I can borrow.

why the lightweight mounts?

Not using them for weight savings - just what Talley calls them. They are simple and highly recommended by some of the top long range hunting crowd as in this pic below from Gunwerks.

Thanks all. Your thoughts are appreciated.

 

[Dogleg]

Now that you mention the Talleys I did have a couple of the ring screws that hold the caps on shear off on those. I was on a grizzly hunt in Alaska and the next time I shot it after I got home the zero had changed and a couple screw-heads on the rear ring were gone. I don't remember what size those screws are, but maybe 6-40? I bought replacements at Canadian Tire and turned down the heads to make them fit the counter sinks. Never really trusted it again so changed to double dovetails which also allowed the scope to be moved another 1/2" farther ahead. Rifle was a Kimber in .338 Win Mag which gets rather lively in the recoil department.

 

[blwebster]

I have not seen it happen on anything I own, but some folks shooting high recoil rifles with heavy optics sometimes opt for the Nightforce Extreme Duty Picatinny rails as they are high quality 1 piece rails machined from steel and have an integral recoil lug machined into the bottom to help reduce stresses on the mounting screws.